Pretty sure I saw a sticky here years ago, on 3rd gen rear end info. I don't see it in any categories, and It won't show in the search bar. Any help would be appreciated. Thanks.

 

Never mind. I finally got to see it listed in the drop down list. Funny, how the "transmission drivetrain" category keeps disappearing.

 

Not sure what "info" you're looking for. There really isn't awholehelluvalot.

There are 2; the 10-bolt and the 9-bolt.

The 10-bolt came in 2 varieties. One about 86 or 87 back, the other 87 or 88 up. Difference is the axle diameter, which leads to a different number of splines. Either 26 or 28. Doesn't sound like much butt the splines themselves are MUCH bigger in the 28 version, making it MUCH larger OD, and thus altogether stronger. Some came with a "posi" which instead of anything "real", was just an Auburn (or in some of the early years, a Gov-Bomb). The Auburn wears out FAST, hardly ever makes it much past 100k miles in anything like "functional" or "working" condition, and then can't be "rebuilt" after it wears out so it's strictly a one-time use then throw away kind of deal since no parts whatsoever are or ever have been available. Some came with drum brakes, some discs. Discs were the ultimate ***** 88-back, the Delco-Moraine system. 89-up is PBR, which are essentially an early version of what came in the 4th gen cars as well.

The 9-bolt is ... the 9-bolt. All except one or 2 were "posi"; again, not a very good version of that: it works well enough, butt wears in such a way, and wears the housing as well, so that it's QUITE a pain to restore it once it wears out. Possible, just, not cheeeeeeep or eeeeeeeezzzzzzzzy.

Past that, what you see when you take off the cover, is what you get. "Codes" are largely a waste of time since so many have worn out and been worked on in the intervening 40 or so years. Not worth the paper they're printed on except for "historical" value; that is, not reliable enough to actually buy parts around. What you see is what you get; not, what the "codes" say is what you get.

 

Thanks for that. I have an 84 T/A with a drum brake 10 bolt. (Non posi, altho it has the " Limited slip diff oil only" tag on it.) I'm sure they're hiway gears inside too, seeing it's a 305, TH700, AC car. Haven't pulled the cover. I'm in the middle of a 301T eng. swap, and a WC T5 swap. Would like to do something with the back, and will end up with a 3 1/2 gear, or 3.73 depending.
Not sure if the carriers have different offsets for steeper gearing. But seeing this rear is a non posi, I'll need to change all the guts anyway. I have a line on 4 w/disc 9 bolt, (very used and crusty) that has a 2.77 (?) gear, (posi) and was wondering if a set of 3.42s could be used on that carrier. I won't be drag racing this car, and the little 301 doesn't make a ton of power, but I'll beef it up a bit, and put it thru some "spirited" driving...just for fun. I would like a step up from the current rear. And the disc addition would be a plus. (Why do these photos appear so large on this site?)

 

Most likely it came with a 3.23. That was very common in cars like that one.

Since it's all spooooged up with that red silicone sealer, somebody has already been inside it. See the last paragraph above. There's NO TELLING what's inside it now. Take off the cover and look; what you see is what you've got. Who knows. I do find it amusing though, that they put that tag on there, if it's not actually posi; of all the poseur crap I've seen people do to cars, that's a new one. Because of course if it isn't posi to begin with, it doesn't need the additive. Or maybe, it started out life as a posi, butt being a POS Auburn, it's completely wore out, and you just can't tell. Again, who knows. Take off the cover and look.

No sense in putting a non-posi rear in a car that's thought to be intended for "performance" or "power". However, the 301 will adequately prevent that, so maybe it wouldn't be that big of a deal. And the ordeal of putting a Pontiac motor into a chassis that it never came in, in 2026, likely means that the car will never drive again, just like about 99.999% of all the people in the "Pontiac Swap" thread in the stickies on the Engine Swap forum. Butt hay, we'll overlook all that, and assume that you come to your senses and decide to do something more intelligent than ... all that.

So, first off, it needs a posi. Posi is a property of the carrier. I don't know of any decent posi carriers available today for those little weeeeenie axles. Meaning, any real-world carrier you can buy, will have 28 splines. Meaning also therefore, you'll need a pair of axles. There's a fair variety of those available, so no problem there, apart from a few $$$. Similarly, nobody sells carriers for 2 series rears that I've seen (3.08 or lower) since nobody doing this sort of thing would do something dumb like that. Therefore you'll end up needing a 3 series 28-spline carrier, gears of your choice, a whole "kit" with all the bearings and whatnot, and axles. Again, nobody in their right mind would sink that kind of $$$ into a drum brake rear, or the early D-M discs either, since they're such GARBAGE. Common-sensical thing to do would be to locate either a 89-92 disc rear which would be the same length as yours and allow you to use your stock wheels, OR, a 98-02 (NOT 93-97) one, and use wheels with the 4th gen offset. Either of those 2 will get you rear brakes that are more or less both modern and actually functional. For the carrier, I'd STRONGLY recommend getting a worm-gear type, which would be either the Zexel Torsen like the LS rears came with (ideally, get one from a SLP car, i.e. either a WS6 or SS, which are stouter than the stock ones), or, a Detroit True-Trac.

AFAIK there are no "thick" gears available for the 9-bolt, to allow ratios beyond 3.08 to be installed on a 2 series carrier. That thing is a dead end and would be a total waste of money. Don't even bother thinking about it; let The Greater Fool make that mistake. (One thing I've learned about humans in the time I've endured this miserable assignment to this pitiful planet is, there is ALWAYS a Greater Fool, and usually it doesn't even take very long to find him/her) Even more so if it's 88-back with the D-M brakes.

 

Hey, no raggin on the 301. (I did enuff of that thru my own lifetime, LOL) I'm more of a 60s, early 70s Detroit fan. The 80s was a new breed I didn't care for. However, compared to what's out there the past 20 yrs (or more) the 80s are lookin pretty good. At least they're still rear wheel drive. (And no computer. OBD1 doesn't count).

This 84 car was given to me, and bodywise is in the best condition compared to my other projects. (73 T/A, and 83 C-30 6.2 dually). And the 301T motor was from a parted car, (around 1990) and has been sittin in my garage ever since. I couldn't give it away. But when I finally acquired this 84 T/A, and seeing I'm a Pontiac purist for the past 50 yrs, I saw this as a marriage made in heaven. A light weight 3rd gen. (compared to the late 2nd gens), a whimpy 301T, backed by an all glass T5, and a weird torque armed 10 bolt, (to finish it off). What could be more coordinated than that? So because I'm 70, and won't be driving it like I was in my 20s, but still want some resemblance of performance, just for the fun of it, I believe with a few bolt ons to the motor, (and removal of the smog crap), the stick shift, and a decent rear gear, I think I can get this car into the 14s. And that's good enuff for me. And as for the Pontiac swaps never been done, (per this sites Pontiac swap history) I know what you're throwin down. But not in this case, it's takin some time, but hasn't been on my priority list. Now with the kids gone, (and an old house that'll never be "done"), my focus is finishing this car..."B4 I die". Hey, ya gutta have a reason to get outta bed, right?

Now, to get down to business, you gave me some great info on these rears. So basically you're saying putting bigger axles, to fit a 3 series carrier, (to accept a 3.5, or 3.7 posi) would be more expensive than locating a 89-92 4WD rear? Are those rears even still out there for sale? I would just prefer to keep most of the mods GM, rather than aftermarket, if possible, and not cost prohibitive. And I really would like to have the rear disc too. And lastly I mentioned the 9 bolt Aussie available, but it seems parts for those are even harder to find than hens teeth. So i guess I'll be hunting for a 90 4WD posi rear. I can put guts in one if needed, and have done other rears in the past. Never a 3rd gen tho. Anyway, I appreciate you takin the time to educate me boss. Have a great week-end.

Geesh. Can these photos get any bigger?

 

No, I didn't say that. Never said anything about 4WD at all, considering that none of these cars ever came that way. What I DID talk about was a 4th gen rear, in particular 98-02. I have no clue what you'd have to pay for such a 4th gen rear, so I can't even make that comparison. Axles are maybe $250 a pair, a carrier is maybe $450 or so, a "kit" $120, and gears $200 - 250. Then, ideally, in order to not waste money on doing all this to a drum or D-M brake rear (i.e. putting 7 tubes of lipstick on a pig to make it into a supermodel), you'd need to find a 89-92 disk brake "core" to do all this too, and throw your drum POS in the trash. THOSE are tough to find. Which is why I brought up the other option, which is, a 98-02 rear, and 4th gen wheels; you might even be able to find one with the gears you want already there, which would reduce the amount of stuff you'd have to buy for it, balanced against the cost of wheels, which if you're gonna be buying new those anyway, wouldn't matter.

Iunno. Depends on if anybody wrecks a car, or parts one out that's rusted or whatever, that has one like that, and the rear finds its way to somewhere it can return to the market. I'd think that would happen from time to time. May require a certain amount of patience however.

 

I hope you didn't mis-interpret my abbreviation "4WD" to " four wheel drive" or "front wheel drive". What I was referencing was 4 wheel disc. In my drivetrain transformation, my #1 priority is the gearing, to improve the acceleration, and drivability compared to lazy gear performance. The disc brake is secondary, but would be nice, "if" I could find something financially feasible. I'm not too keen on the 4th gen rear, if I can't retain the stock 84 wheels. If I need-ta build a 7.5/7.6 drum brake rear with 28 spline axles, and a series 3 posi, with drums, so be it. As I mentioned, I won't be drag racing this car, or dumping the clutch at 3K (very offen). I've seen a ring gear spacer offered for the 2 series posi carriers, to allow 3.42/3.73, and was wondering your opinion on that route. I've seen them offered for decades, but don't think they were very popular, or looked at as a viable option, compared to spending the $ on a series 3 case.
By the way, was wondering if you have any 3rd gens anymore, in your driveway, or what your favorite ride from the past was. Have you any pics in the 3rd gen gallery? I'll have-ta check it out. By your signature, you've been around these cars for a while.

 

In this model of rear, it's not a good idea. Reason being, it has to be about .400" thick to move the ring over the correct amount, and the "shoulder" feature on the carrier in this model of rear for the ring is only about .250" tall, which means then that with a spacer, the ring is no longer positively centered on anything when using one. The "special" "thick" gears are the better option in this rear.

Butt, it's a moot point anyway, since (a) you say you don't have a posi now in the first place, and (b) the carrier you have now is more likely a 3 series, (c) you'll be replacing the carrier anyway to get posi, so you'll just be buying the right thing for whatever combo you end up doing, and (d) you don't want the gears you have, so you'll be buying those as well, which gives you the chance to get the right thing for your eventual setup.

I still have my old 83 L69 car, that I traded in a 79 Z28 for. It came with the T-5 and 3.73 gears of course, no posi (there was a SEVERE shortage of those at the time), and drum brakes. It has about a 96 or 97 T-56 now that I put in it in about 03, and about a 91 or 92 disc rear that I put in it in maybe 01 or so (memory is foggy on the dates) with an Eaton posi (the worm gear ones were REAL hard to get back then, I wish I'd have tried harder to find one of those instead) and the original ratio which I wish I'd have put in at least 4.10 instead, with new axles since stock ones are about as hard as butter and the ones that came with the rear were already fornicated, as usual. It's silver, grey interior, has 4th gen leather seats in it now, kind of a graphite color. Has over 300k miles on the chassis, it's largely beat to hell and used up. Maybe someday I'll renew it.

There are a few (very few) people that specialize in used parts for these cars. Hawks, the board sponsor, is one such. They make a few "modernization" parts as well. No idea how they are to deal with, or what their pricing is like, or any such; I've never done business with them myself. Butt lots of other people here have, so they can't be "too" bad, butt I'll let them speak for themselves. I'd check with them first if I was looking for a core. Might be worthwhile to check car-part.com and such as well.

 

You can find lots of used parts on ebay. Theres a dealer Camaro parts world or something like that. Hawks is great also. Hawks is kind of pricey. Shipping an rear is really expensive. I see them locally all the time. Thats your better move, if you want disks. If you can deal w drums, just get new internals and rebuild your current unit. 3.73s-3.90 will be awesome. I had 4.10s w my t5 and a 430 hp engine for a 500-1000 miles. It was just sooo low. First gear was almost useless. It really depends how the turbo 301 revs. If i remember, its not a revvy engine.

 

Yes shipping a rear is expensive... generally it has to go by common carrier (18-wheeler) on a pallet, so it's not only $$$ to ship, butt also a PITA if you have to unload it at home and don't have a dock & fork lift.

Yes indeed, 4.10 is too much gear for a T-5. I put the original 3.73 back in the new rear I was building back when I still had one of those, although by that time I'd already tore up the original one and rebuilt or replaced it about a dozen times and changed it to a 2nd design one, and completely re-learned how to drive a stick shift, i.e. take my foot off the gas briefly when shifting. Butt then it just wasn't enough gear with the T-56 and its .50 6th gear. There's no "perfect" gear, only, possibly a best choice for the intended usage and combo.

My recollection of the Turbo 301 was that a LG4 in a Z28 (same body that the 301 came in) would outrun it if the 305 had headers. IIRC it was "rated" at about 200 HP or maybe a little more, butt by the time it was all fully installed in the cars it came in, they were like near 4000 lbs. The 301 itself weighs about 150 lbs more than even an all-cast-iron SBC. I DO recall, my 83 L69 ("rated" 190 HP, and maybe 3350 lbs) absolutely DRILLED one of those HARD when I ran against it, when mine was still showroom-floor stock. If I was going to go to all the trouble of putting a Pontiac motor in one of these cars, which one of those motors is enough of an ordeal no matter what CID the motor is, or even without the turbo which is gonna make the exhaust even more of a stumbling block, I'd sure as hell put in a larger one. The only good thing about the 301 is that IIRC it had a short stroke and large bore, like both the Ford & Chevy 302 motors. In its day though, as it came, it was just terrible; no better than the carbed Buick 6-cyl from the same era, before they put EFI on it. Butt hay, that's just me, it's not my project so I'm not gonna tell him he can't do it. Regardless, I wish him the best, and I'll share what I know with him, butt doubt it will end well no matter what gears are in the rear.

 

FYI I just looked at car-part, and there's a disc one in RI someplace. Should be driving distance from anywhere in CT. (at least, I've driven all the way across CT more times than I care to count...)

 

I never heard of this "carparts".com, and glad to see there's more options than just Rock auto, (done them in the past...not a fan), and I live on Ebay. But 3rd gen rears there, are mostly what I have, with a couple disc brake ones that are an eroded 9 bolt, and another one too far away, and too expensive. I looked into the carpart site, and there was one in eastern Ma, but didn't say what the rear was. Just that it fit a firebird. As for Hawks, I'll give them a try too, but if there's nothing local, I won't be paying for freight.

As for the 301/305 comparison, I know all about the benefits, and downfalls. And there is much mis information about the 301/301T, as far as weight goes. With the trimmed down block, and all the thinning and weight reductions, the eng. weighs the same as an SBC. I know, cause I have one, (weighed it) and fully dressed, with a std flywheel weighs about the same as the SBC which is a tad over 550. In the 3rd gen chassis the 301 fits like the SBC. length, weight and height. A touch wider, but nothing serious. I knew when i joined this site, I wouldn't be that welcomed, due to the 3rd gens, (whether it's a bow tie, or arrow head), they're all considered camaros, due to the small block. I've been beaten over it my entire life, and have accepted it. The traditional Pontiac V8 does weigh about 100+ lbs more, (like the King above mentioned), and comes with a few more considerations that the little 301 doesn't have-ta deal with. And the traditional Poncho has the potential to make more power easier than the 301, but once again, I'm not lookin for 400 HP or more, but more like 250-300, for what I'm trying to accomplish. Which is, to have a 3rd gen T/A, with an actual Pontiac V8. Something that Pontiac wasn't able to do, due to the GM ban. And it's funny, because most of the kids today have no clue about what engs B4 the new millennium were, and what they were capable of. If they hear my car has a "turbo', they'll mostly think it's really "fast" (LOL). But hey, fast is a relevant term. There's always somebody faster, no matter what you have. With this car, I just wanna have some fun with it, by making it pure, and with a stickshift, and a 3 1/2 posi, with the style and light weight of the 3rd gen., it'll do all I want. i just need-ta get off my dupa, and get to it. Am "indisposed" this week-end due to obligations with grandkids visiting, from NH, but hopefully will get back out there this coming week, after work.

So, to you fine people helping me along, sorry to bore you with my tales, and at the "King" enjoyed your stories of the past. Good to have memories, and hopes for future ones to be made. OFN

 

I think this is an awesome swap. Pontiac was gonna build the TAs this way till gm killed it. I live in CT. Im hoping to see this car ripping around then its done!

 

Thanks FC. Maybe we already went to the same place. Did you ever go to Marks Auto cruise nights? (Mon.) there were a couple super clean 3rd gens with LSs. One was a 6 spd, the other an auto.

 

Not sure about "carparts" or "carpart"... rockauto only sells new parts and doesn't part out cars anyway, therefore is the wrong kind of place to look for an antique used part like a rear axle regardless ... and ebay, while valuable sometimes, is very much hit-or-miss as to availability of any given part at any given moment, and then the price, condition, quality, seller honesty, shipping arrangements, etc., for any given part that DOES appear there ... the site I sent you toward is car-part.com, which is some sort of aggregated listing of parts in junkyards. Not sure how the listings get there, like whether the junkyards subscribe, or what. Just click on the link and don't try to spell it. You select the vehicle model & year and the part you're looking for, and your zip code, and it searches the country for that part, showing them sorted by distance. I put in the rear axle assy for 92 Camaro; since Firebird is the same thing anyway, just with different sheet metal wrinkles and cup holders, those come up mixed in with Camaro ones. Try it and see.

 

never went to one. Im usually around the newtown area.

 

The site is the same as the one I looked at, but when I entered my data, (the 1st time) I clicked on the drum brake option, just trying to see what would come up. This time, I clicked on the disc brake and low and behold, the one you mentioned in RI appeared. (!). For a great price of $500+. From a 92 FB, with 180K. But the housing has extensive rot, not only on the spring mounts, but one photo appears the axle tube has a hole in it. (If I'm lookin at it right). However, I believe a close-up of the metal tag, shows a "3.45" gear ..."maybe" (?) if I'm reading it right. I think I've seen other tags, showing a 2.77 number, being advertised as a 2.77 gear, on different rears. So could this one actually be a 3.45 posi? Would there ever be a 3.45 "non-posi"? But it has the staggered disc set-up. That's gutta be better than the drums, right? And one last question. Would all the parts interchange with my 84 housing? (Pinion brgs/ carrier brgs, ring gear diameter/axles and lengths). Or not? I think it would be too good to be true.

 

You missed some good shows. Many times he had upwards of 1000 cars. It was a local junkyard, but out frt he had acers of empty grass fields, and he would load the place up, every mon. nite for about 20 yrs. (Depending on weather). Had DJs, food booths, awards for the best...And the crowds never dwindled over the years, but he just got too old to bother with it. Closed down a few yrs back. A shame. I think I took some photos of his last event. it was 2021.

 

The parts between the older axles and newer axles don't play well together. I think the axles on the newer ones are longer, the unit is slightly wider. Personally, i wouldn't buy a used rear and expect any of the internals to be good. Back in the day, we beat the hell out of these cars and killed rears pretty often. Also reusing/swapping old gears is iffy. The R&P have established a wear pattern and trying to replicate that pattern in a new housing is iffy. Its doable, but requires skill and patience.Also the early disk setups are terrible. I strongly recommend a more modern brake setup or sticking w the drums.

i do see rears on CL frequently in CT/MA/RI.

 

I see the 4th gen rear is wider, but it appears all the 3rds are the same. And I just found the sticky/FAQs, (on 10 bolts questions) on this site, which is very informative. Point taken on your advice FC. I'll check into the C/L for more possibilities too. Thanks.

 

If it's a 10-bolt, no.

Gear ratios are always the ratio of 2 whole numbers. The numbers are the tooth count on the ring, divided by that on the pinion. One of them is virtually always a prime number, sometimes both. A prime # guarantees that every pinion tooth mates to every ring tooth before repeating, and each tooth mates with the other an equal number of times over its lifetime. 3.73 (3.727272727272...) is 41 & 11: both are prime.

10-bolt gears have more teeth than 9-bolt ones do. Like everything else in life, it's a tradeoff; more teeth means that each is smaller and therefore weaker, butt smaller tend to make less noise, and generally have lower loss (better gas mileage).

10-bolt ratios commonly seen include 2.73, 2.92, 3.08, 3.23, 3.42, 3.73, 4.10, & 4.56. 2.73 is 41 & 15; 2.92 is 41 & 14; 3.08 is 40 & 13; and so on. 3.42 is 41 & 12. 41 ring teeth seems to be a popular number with GM in these.

For whyever then, 9-bolt ratios have fewer teeth. The commonly seen ratios in those are 2.77, 3.08, 3.27, 3.45, & 3.70. 2.77 is 36 & 13, 3.08 is 37 & 12 (rounds off the same to 2 decimal places as the 10-bolt ratio butt isn't exactly the same), 3.27 is 36 & 11, 3.45 is 38 & 11, and 3.70 is 37 & 10. All 9-bolts, with only 1 exception that I've ever seen, are posi; the ONE is a photo that someone posted on here years ago, and it shocked most everybody, because nobody had ever seen one. So, not "all", butt maybe "all butt one". I find that hard to believe in a mass-produced product, butt hay, if they did it, then they did it.

The last year of the 9-bolt in these cars was 89. Therefore if it's REALLY a 92 rear, it can't be a 9-bolt, and therefore can't be 3.45. Could be 3.42 butt I'm not sure there were any 3.42 rears that year; if so, it would have been in a 5-speed car w G92 option, a very much maxed-out combo, if it existed. That said, the 9- and 10-bolt are the same externally, therefore directly interchange, so it's possible that somebody stuck a 85-89 9-bolt in a 92 car. Without seeing the rear itself I couldn't say what it is for sure. It could be a posi, or that is, it may have come with a posi; butt if it's a 10-bolt it would have been the steaming bucket of s*** Auburn, and as such, hot festering GARBAGE. If it's a 9-bolt, and from 85-88, it will have the D-M rear discs, which are even worse than the Auburn carrier, and even worse than drums. You DO NOT want those. If it's a 89 rear, with the PBR brakes, then those are the brakes you want, and it's a somewhat decent choice; although the odds of its posi being worn out are very high as well, and while it's possible to renew that, it's not cheeeep and not trivial (it's not just parts you bolt in, machine work is required).

The 4th gen rears are about 1-5/8" wider on each side, therefore about 3¼" overall. Putting one of those in one of these cars with our stock wheels looks STUUUUPID and poseur, and ESPECIALLY with those tiny 14" & 15" ones they used in 84: these cars' wheels are little skinny pizza-cutters by modern standards, and having pizza cutters that stick out past the fender wells looks ... well, there's ALOT of inappropriate slurs that some people might be tempted to use to describe it. I'll just say it looks like cold leftover yesterday's A$$, in a word. OTOH with 4th gen or C4, 5, or 6 wheels (or aftermarket to fit those) they're in exactly the same place as our stock wheels, and with newer wheels like that, you get modern driving capability, and tire sizes you can actually still go to the store and buy in a QUALITY brand (Michelin, Pirelli, etc.) along with load & speed ratings suitable to its weight and performance. I would NOT hesitate to put 4th gen or Vette wheels on one of these cars, myself, if it came to that. Oh wait... I have a set of C5 wheels on my car now, although since I have a 3rd gen rear, I had to use wheel adapters on both front and rear to get the offsets right.

 

Wow Mr. King, and I thought "I" was the only one wearing out my ribbon cable on my dot matrix. You have quite the knack for filling in the blanks. Once again, appreciate the info and advice.
I believe the rear in RI is "not" sold as a 9 bolt, but a 10 bolt. (Not sure why the 3.45 tag) That's why I was asking if the guts would interchange into my 84 housing, (If it is a 92 10 bolt).
I just saw Hawks offers a 3.42 R+P, "and" a clutch type posi unit for $400, which isn't unreasonable to me. Still would need 28 spline axles, and an O/H kit, not including a disc brake conversion. Went onto C/List to see if there are any 3rd gen rears available, but to no avail. Waiting on a couple replies from Ebay sellers...probably tomorrow.
And just now, I pulled the rear cover off this 84 10 bolt, to find it "is" a 3.23, with one of these totally weird carriers, that I saw once in my life before, (in something like a Grand National rear), but have no clue how it operates. What kinda lunatic would come up with this design, in a rear? I know all about clutch and cone diffs, but this (?) totally blows me away. When I rotate one tire, once (for a second) I saw both wheels turn the same direction, then not. When tried again, only one will turn. The other doesn't go the other way. And I can hold one, while turning the other. I can't wait to hear the explanation of this conbobulation.



.

 

Sofa will properly ID and have some amusing commentary on the performance, but I believe thats a gov lock (gov bomb) locking diff. I thought they were only in trucks. To be honest, if its a working locking diff and a good R&P, leave it till you find exactly what you want.

 

That is an Eaton Gov-Lock. Aka Gov-Bomb, Grenade-Lock, etc. ABSOLUTELY UNEQUIVOCALLY POSTIVELY NOT a "performance" piece AT ALL, in any manner way shape form or fashion. It was originally designed for small military off-road vehicles with a real small diesel 4-cyl or some such. Works GREAT in that sort of application; not so much in any kind of application where pavement, power, and traction are involved. GM put them in S trucks in the 7½" rear, and full-size trucks in the 8½" one. My Avalanche had one originally. I think they're even in the 9¼" (14-bolt). A few of our cars, back in the posi shortage days, got those; more likely though, Stimpy got one out of a S truck and slapped (threw?) it in there.





The way those work is, there's NO POSI BEHAVIOR WHATSOEVER (acts like an "open diff), until the RPM difference between the axles reaches something like 100 RPM. At that point, one or the other of those little governor weights, depending on which axle has the higher RPM, moves outward, which engages a "dog" which engages a clutch. In a low-power, poor traction situation (off-road... sand, mud, wet grass, ...) it works GREAT. In something like our cars though, the engagement is so sudden and violent, that it EXPLODES. There was a post on here some years ago from someone whose ... that ... exploded SO HARD, that the shrapnel went THROUGH THE COVER, and INTO THE GAS TANK. Lovely. Just what we all want: red-hot sparking metal launched into the fuel.

Which is why it acts like an "open" most of the time; butt if you spin one axle fast enough (it's easy to do by hand if the tires are on it) to reach that magic threshold, it locks up, and pretends to be a posi for awhile. It kinda stays locked up until the force imbalance goes the other way, which kinda "resets" it.

 

You guys explained it as I just got educated from the net. It looks to have the strength of a harbor freight 1/4" ratshit. Most pathetic design to ever come out of Detroit. (Much like the design of the 301 Siamesed cylinder head ports, and crankshaft with 2 counter weights.). Are these (were these) engineers on drugs, or what? The common sense technology born from the great engineers of the WWII age, I guess has long been lost from now-a-days generations. Well, I guess these 80s designs can't really be blamed on todays technology, but on the Viet Nam/LSD generation.

Anyway, I'll still be lookin for better mods to mine, but this thing behind the little 301 (like FC suggested) will be tolerable, if nothing else becomes available soon. I'll just bullet proof this rear, by filling with Amsoil, "slick 50", GM posi lube, and maybe a squirt of Locktite. I think JC Whitney might have a miracle additive too.
And lastly Mr. King, those were some pretty "explosive" photographs. Can't say they're surprising tho.

 

I wouldn't say it's "pathetic"; just, while perfectly well suited to the application it was designed for, it is NOT suitable when power, pavement, traction, and shock are present. Not sure why GM puts them in full-size trucks either.

Pretty sure the Gov-Bomb doesn't need posi additive. GM specifies synthetic 75W-90 for my truck for example. Doesn't mention friction-modifier additive at all. Not sure what Eaton themselves call for. There's no "bullet proofing" that thing with fluid in any case, it's still gonna be just as fragile no matter what.

The thing to watch out for is a sudden one-wheel-peel in a low traction situation, like a hard launch followed by a slick spot such as wet or sand, followed by a sudden restoration of traction. If the rear's lockup and the application of torque happen together, that's when it can explode.

 

Funny guy. My bullet proofing comment was "tongue in cheek", (Wasn't serious) But I still think that gov/bomb is a crap design, even for a 4 sillywinder. All the complications of machining that thing, and I'm sure most drivers wouldn't know the differences between it, or clutches. And because the old design worked well for so long, I'm betting the tooling was already there to continue building, rather than re-inventing the wheel. Wondering what Detroit is using now-a-days, that a computer isn't controlling.

 

Well, as far as GM was concerned, there really wasn't any "tooling" at all; that thing bolts in just the same as any other carrier does. As to why they used it in so many applications, even where not really appropriate, I can't begin to guess.

Since Eaton made the original "posi" back in the 60s, and they also made ... that, maybe they dressed up a pretty girl as their sales rep to GM, and worked that angle of things, to sell it where the actual "posi" would also have been inappropriate, and they would otherwise have lost a sale. Stranger things have happened. I have no clue.

Those were still being installed in trucks as the infamous "G80" (GM's RPO for many decades now for "posi", NOI) at least into the 20teens. Not sure if they're still using it or what.

 

I was referring to the tooling needed to "build" that new torsion design, not installing it. It looks much more elaborate, with all them intricately machined "components" that looked severely undersized, to accomplish what's needed in that environment. And you say Eaton is the manufacturer of that thing? Shame on them.
Hey Mr. King, was wondering about your opinion on the ad below. I know you mentioned the 89 on up rears to be superior, but this rear has 3.73s, and discs, with a super price. What if I bought a posi for it, then I would have a good gear, posi, and discs. For less than a grand total. I'm waiting for confirmation on the erosion condition. It's gutta be better than what I have, and behind the little 301, i don't think it would be that bad, once all is gone thru. What-da-ya think Boss?

https://www.ebay.com/itm/14704536474...6algo%3DPERSON

 

That's just it: GM doesn't "build" them. They BUY them from whoever. Eaton in the case of the Gov-Bomb, Auburn for most of the "posi"s in our cars, Borg-Warner for the 9-bolt. Stock 10-bolt gears come from American Axle & Machine. Delco-Moraine, the maker of the super crappy 70s & 80s discs, was a GM property, butt PBR is an Australian company. GM makes the 10-bolt axle housing still I think (they bought the 9-bolt complete, housing and all, from B-W), butt EVERY SINGLE PIECE inside it comes from a subcontractor. I'm not thinking you realize how little car manufacturers actually "make" anymore, or even how pervasive the outsourcing was even back as long ago as the 80s, and GM is far from the extreme of this. More and more, ALL of them buy that sort of stuff from global companies that supply EVERYBODY in the car assembly business. Like, Brembo makes brakes for Porsche, GM, various other European car companies I think the Koreans (which the Hyundai and Kia brands are the same company), and so on; the car companies don't want to be concerned with that level of detail. The car "mfrs" merely purchase and assemble sub-assemblies from whatever source, stamp the wrinkles in the sheet metal with their own "styling cues", install the cupholders, and sell the finished product through their networks of franchised STORES aka "dealers". Car dealers, GM dealers specifically, are the origin of the "franchise" business model; been doing it LONG BEFORE fast food. GM had probably been doing business that way for DECADES before Ray Kroc (the guy that bought the original McDonald's burger stand and turned it into what we know today) was even BORN. IMO all that "real Pontiac" crap is just that, CRAP; people that say that are falling for the branding, without realizing how shallow and insignificant it is, overall. It's mostly LITERALLY just wrinkles in sheet metal and cupholder type details.

I'm not a Firebird brand person, so I don't know what year that car is. Looks maybe 87ish butt I'm not sure. Definitely doesn't look like 89-92 to me butt I could be wRong about that.

If it has the D-M discs, which any 82-88 rear-disc car would have come with, I'd pass, for myself. Keep looking. Be patient until you find one with PBR brakes. 89-92. I cannot stress this strongly enough.

I wouldn't worry about ANY stock 3rd gen 10-bolt posi. Again, they're all TERRIBLE; they're either the Auburn, or occasionally the Gov-Bomb. The only 7½" 10-bolts that have anything else are 98-02.

Gears are $200 or so. Barely a blip in the whole $$$ equation of this type of project. Virtually EVERY 3rd gen 10-bolt is gonna need axles and a carrier; you need most of a "kit" to put those in; the only extra "kit" pieces for gears, are the pinion bearings & seal, and its shims.

In my opinion – and it's just "opinion", and as such is worth exactly what I'm charging you for it – the thing you should do is keep your money in your pocket until you find a 89-92 disc rear; throw away every single internal moving-part piece and keep only the housing and brakes; and put gears of your choice, a good worm-gear "posi" carrier (either a Torsen or a True-Trac), and good quality axles in it. No 82-88 rears no matter what internal parts come in it that you're just gonna take out of it and throw away. "Posi" doesn't matter because anything you get is garbage to begin with, and likely already worn out. Gears don't matter since even if they're a ratio you want, they're used, and are a substantial failure risk that's not worth taking, since they "save" so little $$$ to begin with. For that matter, if you already have a set of 3.73s in your current rear, and you trust them, you could re-purpose those, at lower risk than buying something at random in unknown condition. Axles don't matter because stock ones are almost all already DESTROYED where it matters, which is, where the bearings ride on them; they ARE the bearing inner race, butt are not made of bearing-race-quality material. Just my opinion. All of that stuff is easy to buy and install; brakes, not so much.

 

Gut-cha king. I'll just baby the pos I have now, and wait for the 89-92. Maybe someone will part with one...B4 I die. Thanks a bunch. OFN

 

Swap meet find. A person wanting to M/T out his garage, selling these rears....for literally pennies on the dollar.



The red rusty one(?), an 89 10 bolt 7.6 2.77 open, (thrown in for free).The black one, a 4th gen 3.23 Eaton clutch style posi, a step up from my gov/bomb. Less than $50 for both.
I figure the posi alone was worth it, and the rest is extra...????. Figure I can leave my gov/bomb 3.23 drum brake stock 10 bolt alone, and put together this 89 rear, with the posi, and now looking for ..."everything else". Wonder if them Corvette wheel adapters are worth anything, to anyone?

 

If it is, it's not stock. GM didn't put Eaton carriers of that kind in those cars. Would have to be an $$$aftermarket$$$ one if it's an Eaton.

Look at it closely. If you see this logo on it, probably near the driver's side carrier bearing, it's an Auburn, like all the other posi units GM used in 4th gens before they switched to the Zexel Torsen in 98, and is likely not worth building into a new project due to its poor longevity.



It's a kinda stylized "A". The carrier itself will look much like these.



An actual Eaton posi will look like this.

https://www.summitracing.com/parts/etn-19599-010

Note the price: it's not likely you're getting one in a $50 pile of used parts. Not "impossible" of course; just, not all that likely.

Looks like you tried to post 2 photos. The one on the left doesn't work, only the one on the right, that shows 2 pairs of stock-looking axles, and some other parts, butt is from too far away to see very much detail.

The wheel adapters might be worth something to someone; maybe even yourself, eventually. If they're about 1¾" to 2" thick, they'll allow for C4 or newer, or 4th gen wheels, on one of these cars. Maybe as in, if you wanted to put a 4th gen rear in your car, say to get the better brakes, and want 4 matching wheels, then you might use 4th gen or Vette wheels either stock or aftermarket, and those adapters on the front. You'd need 4 of them to swap the newer wheels on with a 3rd gen rear; the ones on the rear would typically want to be slightly thinner than the ones for the front, maybe like 1¾" on the rear and 2" on the front. That's the combo I have on my car, with a 3rd gen rear and C5 wheels.

The red paint on the drums makes me want to hurl.

 

"There he is!" (LOL) Welcome back, and thanks once again for your incite SK.
So for yrs I've gone to this automotive swap meet every spring and fall, ( since I left the good ole USAF in 81, and came to this great state of CT...) And ever since this 84 T/A project came to fruition, I've wanted a 3.73 posi, with discs, not knowing much about 3rd gens. (I stopped caring about Detroit performance cars after 73.) But when this 84 became available to me early 2000s, (and the 301T was buried under a bench....since 1990), I decided to make it a combo, with the intent of getting better mileage than 12-15, (that all my previous street Pontiacs got). Then I heard the 301T and good gas mileage was an oxy-moron, so that desire went away too. So now, I'm just looking for an entertaining street car, that I might take to the track to see what kinda times it'll do, and maybe a bit of spirited driving on the street. No slicks, or high torque, 3500 RPM clutch drops, with full powershifts. At least not anything like how I treated my GTOs back in the day. And I won't be remortgaging my house either to put this car together seeing retirement isn't but a yr or 2 away.

So, back to the swap meet. Because the 3rd gen rears with the guts and brakes I want are as rare as hens teeth, it doesn't keep my from lookin for one. Not many 3rd gen rears are ever for sale, at least around here, and these 2 caught my eye. The seller rushed right over seeing my interest, and I told him I was lookin for a 3.73 posi with disc, and he reply's, "that what this is". (right next to it was the open 2.77 3rd gen) . Says he has an 89 T/A at home, (showed me a pic of it on his phone) and said he uses it for some kinda low budget circle track racing. But these rears were in the way for yrs, and he didn't wanna bring it/them home. I asked him to pull the cover so I could see the guts. (By the way, he told me it was a 4th gen rear) . And I believe this site, (maybe you SK) informed me the center sections are interchangeable, with only the axles being longer. And low and behold, it wasn't a gov bomb, but the typical style I'm use-ta seeing. "However", turns out, it wasn't even 3.73s, cause after turning the axle, and counting the revs, it's nothin more than 3.23s, which turned me right off. And when I see what the aftermarket wants for posis, I decided I'ld take it, just because it was better than the gov/bomb, that I don't trust as far as I can spit. But this Auburn unit's gutta be better than what I already have, and he asked me if I wanted the 3rd gen rear for free, just to get rid of it. So I took them both to build on it, (the 89 rear) rather than take apart the stock one in the 84, that already mentioned. So, for the price, I'm not complaining, and I'll keep my eyes open for a set of 28 spline axles, and something with a disc changeover. I will spend some $$ on a set of new 3.42s, or 3.73s, and of course new brgs.


So SK, you said both my previous photos weren't viewable? I don't know why. I can see them in this thread. I'll throw these at you, and see if you can see them. (By the way, I tried opening up your link for the Eaton posi at Summit, and it won't show either). But I did go to Google images and saw it there. They look the same as the Auburn to me, but I'm guessing they have Kryptonite spider gears, an Inconel case, titanium springs, and Kevlar clutches to warrant the extreme pricing.



And lastly, you mentioned how much you enjoyed the red drums, (LOL), if you want them, you can have them for free. (just shipping) You can use them as freestanding bench grinder bases. I'll even toss in the 26 spline axles to mount them on. What-da-ya think?

 

Hard to say why I couldn't see them. All I got was the Photobucket generic F-you image. It's better now, I guess you fixed it.

Similarly, no idea why the link doesn't take you to the page at Summit. Maybe all of this is just the Interwebz's way of reminding us that Algore didn't get it perfect when he invented it.

That posi is an Auburn. Just a stock one at that, not even a "performance" aftermarket one. You can look at the pic of those 2 I posted; the left one is a stock 2 series, the right one is an aftermarket 3 series. Big difference (apart from the ratio series): they added a spring or 2 to the clutch plates. :whoopee: Yours is definitely from a 4th gen with the 3-channel ABS though, with the tone ring on it. I strongly encourage you NOT to put it into a "new" "fresh" rear end build.

The Deal is, the purpose and function of that type of "posi" is to use clutches to lock the 2 axles together, butt in such a way that if both wheels have traction, it will yield, and still let them turn at different speeds, as required when going around a corner. Meaning, it suppresses the unlimited one-wheel-peel of the first tire that loses traction (usually the inside one in a corner, and especially if it's the right one) that we all know and love so well, butt the MAXIMUM torque it can deliver to a wheel that has traction while the other doesn't, is limited in turn by the hookup of the clutches. So, it's a sort of balancing act. Too much clutch, and the rear chatters ruthlessly around corners and such, ALL THE TIME, if both wheels have good traction; butt too little, and instead of 4000 ft-lbs or whatever exists at the axles (whatever your motor makes times transmission and rear gearing), you get ... whatever the rear's clutches take to break loose. Most clutch-type units, that's in the 60 - 90 ft-lb range. Which is better than nothing, butt still acoupla sandwiches shy of a picnic.

To test a posi carrier, you hold one axle still, let the drive shaft spin freely (in neutral, if it's in a car), and try to turn the other with a torque wrench. A stock Auburn in brand-new condition is at the lower end of the range I gave you; let's say, 65 ft-lbs. If you can rig up a way to set up that test, you can check it before you devote money to installing it.

No idea why Eaton charges so much for that. They WERE the original that GM bought back in the 60s though, and GM gave the trade name PosiTraction. Frod & Xler bought them too, and gave it their own trade name, butt I can't recall what those were. Pretty similar overall though. It wasn't until well into the 70s that they had any serious competitors at all. I recall a company at that time named Tite Brothers, that sold Eaton carriers that they had specially massaged or added springs or whatever, to make them hook up better; they called their finished product some name that was a mis-spelling of "posi" uncomfortably close to a familiar coarse slang word for female private parts; their slogan was "nothing feels as food as a Tite [product]". Those were the daze. These days though, anybody in his right mind, will buy a worm gear unit rather than one with clutches, especially since they're about the same price. Eaton makes one of those too nowadays, so today, they're competing with themselves. Eating their own young you might say. How charming. Anyway...

No drums for me, thank you just the same. They have NEGATIVE value to me: I've PAID people to come haul piles of em off my property. They're worth more to me GONE than they are in my possession. So please don't inflict them on me.

Gears generally have some indication of their ratio stamped around the edge of the ring. It'll look something like 42:13 on stock 7½" 10-bolt gears (42 ÷ 13 = 3.230769230769230769230769...). Makes em eeeeeeezzzzy to identify. Saves you the trouble of even having to manually count the teeth.

 

I don't count teeth anymore, if they're attached to a posi. Just mark the axle at 12 to the tube or backing plate, spin it one revolution, and count the mark on the companion flange. But I'm sure you already knew that. On my 84 ring gear, the ratio was stamped clearly into it, so even Stevie Wonder could see it. On the one in the 4th gen at the swap meet, it was so unreadable, none of us could see it, and the seller wanted to count the teeth, that were full of oil, and a pinon buried behind the diff. I don't think so. Being a posi, it was easy the other way. Some people say you can figure the ratio on an open diff, by....rotating the axle, and counting it, and doubling this reading, while holding the brake cable between your teeth, and pushing on the shock mount...or something of that nature. Don't know. Just that if it's an open diff, I don't care about the ring and pinion. I'm usually not running the salt flats.
And I'm sorry I can't talk you into the drums SK. I'll hold them for a short while, in case you change your mind.

 

Hey, I just thought of something. Is the stock rear in my 84 10 bolt with the gov bomb, 26 or 28 spline axles? (Just outta curiosity's sake.)
Never mind, I just found it here on the 10 bolt section of "trannys and drivetrains". It says all 84s (posi or not) were 26 splines. Figures.

 

Yup, if it's original, 26. They changed to 28 in 89, more or less.