I went to 9bolt.com based on a post someone made on here, and they claim there are no new 9 bolt parts available. I assume this is true? I want to convert both my 86 TA and 88 IROC to 3.27 gears from the 2.77 that's in them now. I would prefer to use new parts, as both are very low mile, original examples.

I have never done a gear swap before. If anyone can give me some help or advice on what to do, I really appreciate it. I want to keep the original axles. From what I have seen so far, I need to buy a new (used) ring and pinion and a rear carrier, as apparently the 2.77s use a different carrier than the other gearsets did.

Does anyone know what speedo gears I would need? Also, wasn't a 3.45 available in 86 for the Trans Ams? Would I be better off going with a 3.45 for the weaker 305 in that car? I'd like to keep within stock-ish parameters with these 2 cars for the sake of originality.

Any help is really appreciated. I had no idea owning two 9 bolts would make life difficult!

EDIT: Will the OEM posi units in both work with the new gears and carrier? I've seen "mini spools" and such available on 9bolt.com, but have no idea what one is.

3.45 was available AFAIK with certain option combos (LB9, T-5, G92) in both Firebirds and Camaros. In fact, I think 3.70 was available in 85 in L69 Birds (similarly equipped Camaros in that year would have got 3.73 10-bolts I think) but I could be mistaken. ALL of these halfway decent ratios were available ONLY with 305 and manual trans. 3.27 was the highest available in that rear with either a 350 or an auto trans.

Yes, 2.77 and 3.08 use a 2-series carrier, and 3.27 and up use a 3-series carrier. No AFAIK there are no "special" "thick" gears for the 9-bolt, to put 3-series gears on a 2-series carrier.

Can't help you with where to get stuff; all I can tell you is what works and what doesn't. Wanting it real bad won't miracle it up unfortunately. You and everybody else who has one, wants parts for that thing; I'd suspect, if there was a reliable source, you'd see a bunch of people ALL OVER IT on these pages. Don't count on it. Now as we all know, absence of proof isn't proof of absence; but I'd say in a case like this, it's pretty compelling evidence.

Long term, I seriously doubt that originality, or "low mile examples", are going to count for much. If you want your cars original, just leave em alone. If you want different gears, come to grips with, that they won't be original any more. Of course you could always just put your original stuff on the shelf against the unlikely event that "original" ever does become an issue.

1) I thought I had read in a period road test in Hot Rod that an '86 TA had 2 optional ratios. That's never made sense to me...I figured 3.27s were the best available.

2) Will my posi units in my current 2.77 rear ends work with the 3.27s I want to add? I assume yes, but want to make sure.

3) I won't start the discussion of low mile examples being worth something That's for a different section of this board. I have no issue with "coming to grips," as you put it, with putting optional gears in either car. But, I do want to use the original rear ends...I already have one 3.73 10 bolt cluttering up my garage, waiting to go in my RS. I don't need to collect two more! And yes...I think having a numbers matching rear end is a nice thing...maybe its just me.

Any additional help is really appreciated.

Therefore,

would be a "no".

I know you don't want to hear it, but it's the truth anyway, and stubbornly resisting it ("ostrich mode") won't mnake it go away: this is why you need to make a clear-cut decision between "original" (probably not of any value) against having your car the way you want it (I think we can all agree that this is pretty valuable). Life is full of compromises. We don't get to have everything all just the way we want it all the time, without ever having to give up something in return. Like I said, if at some point in the future the value of "original" comes around to outweigh the value of having your car FUNCTION the way you want it, you can put your original stuff on the shelf and reinstall it at that time. Otherwise, you're stuck with (a) finding a 3-series carrier, and (b) finding the better gears, and (c) periodically dealing with the wear-out problems that the 9-bolt carrier has, if you drive it much. Personally, I'd ditch the 9-bolt in a New York instant, if I were in your shoes.

There are no "numbers" on rears to make them "matching" anything. Don't worry about that. Not that anybody is ever going to look, besides.

and (c) periodically dealing with the wear-out problems that the 9-bolt carrier has, if you drive it much. Personally, I'd ditch the 9-bolt in a New York instant, if I were in your shoes.

They don't wear out any faster than a weaker 10 bolt posi. As for parts, you can still find 3 seiries carrier's on ebay and in salvage yards, the cones can be bought from 9bolt.com, with a set of new NITRO gears, you can rebuild a 9 bolt for about the same price as a 10 bolt and have a stonger rear, In most cases all you need to do is shim the cones to tighten up the posi.

10-bolts, if you wear the posi out, you can rebuild or replace them.

9-bolts, you can maybe sometimes buy cones for them that don't fit from halfway around the world (not everybody that's tried has been successful it seems), and machine them down. Who knows what you can do when the carrier dies.

Anything to do with the 9-bolt except gears (which are still available in a few places at least temporarily) is becoming increasingly problematic. Which is why, if the OP is concerend about "originality", he needs to quit driving on it, and put it on the shelf, and drive something else that's actually serviceable over the long term. If strength is an issue, put some other model of rear in it, such as a 12-bolt. Long-term, if strength is an issue, a 9-bolt will tear up and that will be the end of that, ANYWAY. Not good for originality.

It's just LOGIC, combined with facts. I'm not romantic about this stuff; just a realist.

1) I appreciate the help here, but I'm not trying to be an "ostrich," if you will. I know absolutely nothing about rear ends when it comes to the working internals of them. Asking if my posi units will work has nothing to do with having my head in the sand...it has to do with having no real idea what bearing a carrier has on a posi unit. So to do this right, I need a posi unit, gears, and a 3 series carrier, correct? Just looking to clarify.

2) This has nothing to do with strength. This has to do with ditching horrific 2.77 gears in both cars. For 2 cars that will be driven a combined 2,500 miles a year, tops, and not drag raced, I'm just looking for some more enjoyable acceleration down the open road. I will never wear out, let alone blow, either rear end.

3) I have a 10 bolt sitting in my garage...a 3.73 unit from my friend's L69 '83 Z28. Are there any conversion problems swapping to a 10 bolt, or does it bolt right in? Because the rear has about 170k on it, I would rebuild it anyway. I was planning to swap it into my 3.08 geared RS...but maybe the better option would be to swap the gears in the existing RS, and use this 10 bolt in another car?

I appreciate the help. I don't know what I don't know, which is why I'm here.

The 9- and 10-bolts are directly interchangeable, subject to whatever differences involving the brakes. There are 3 kinds of brakes that came on these cars: drum, discs w Saginaw cast-iron calipers 82-88, and discs w PBR aluminum calipers 89-92. If the brakes differ, you'll have to deal with that, independent of which rear model they're on.

The carrier is the big thing in the middle of the rear that the gears bolt to. It is the thing that makes it a posi, or not, as the case may be.

The "series" of a carrier has to do with the location of the ring gear flange.

THINK about the concept of "ratio" for a minute. That is usually taken to mean, the # of teeth on the ring, divided by the # of teeth on the pinion; which is of course true. However, it is also the ratio of their SIZE. in a 3.73 gear set, the pinion is 1/3.73 times as large as the pinion; in a 2.73, it is MUCH larger, specifically 1/2.73 times as large; and so on, for any ratio. Since the ring is ALWAYS the same size in any given model of rear, that means the pinions are different diameters. Now think about what that means, in terms of the side-to-side location of the ring: it should be obvious that the LOWER the ratio, the FARTHER from the pinion centerline the ring must be. So, imagine that you were designing a rear, starting from the lowest ratio you wanted to make available: you'd start out with the flange on the carrier that the ring mounts to, just far enough away from that largest pinion, to fit the thinnest ring you thought you would use. Then the next higher ratio the pinion would be smaller, so the ring would be thicker; the next higher ratio than that, the pinion would be a little bit smaller still, and the ring a little add'l thickness; and so on, up until you reached a point where the ring became SO thick that it's hard to make (heat-treating a real thick thing warps it, so eventually you'd reach an unacceptable scrap rate). At that point, you'd stop the natural progression, move the ring flange on the carrier over toward the pinion, and start over again with the thinnest ring, and begin the progression all over again.

It happens that in both the 9-bolt and the 10-bolt, this happens between 3.08 and the next higher ratio (3.23 in the 10-bolt and 3.27 in the 9-bolt). 3.08 and down are called "2 series" and 3.2x and above are called "3 series". Here's a pic of the difference. These are 10-bolt Auburn :barf: posi carriers; a stock 2-series on the left, and a "high-perf" 3 series on the right.



Note how the one on the left, the ring flange looks almost flat, where the one on the right, the ring flange is cone-shaped on the back. THe reason is, the ring is about .400" closer to the pinion in a 3-series carrier in this model of rear. The 9-bolt is about the same difference.

THis is why, for some (popular and common) models of rear, you can buy "thick" "special" 3 series gears, at extra cost, to put a higher ratio onto a 2 series carrier; but these are not available AFAIK for the 9-bolt. You have to have a different carrier for that model of rear.

Thanks very much for taking the time to explain that to me...I really appreciate it. I think the new plan is to leave my 10 bolt in my RS, putting fresh 3.42 gears in it. I'll gut the spare 10 bolt I have, put 3.42 gears in that one, and put it in the Trans Am. For the IROC, I'll probably pony up the time and money to do a proper 3.27 9 bolt in that one.

Thanks for your help...much appreciated. Before this post, I didn't realize how hard it is to find 9 bolt parts.

The current one with 2.77s in it is almost worthless, unfortunately. Ive gotten those for around 50 dollars or so. If your dead-set on using a 9-bolt, buying a complete one with 3.23 or num. greater gears would be the best bet, but theyre hard to find. Youll need to watch out for the limited slip, tho. I have one sitting out in the part heap that has cones in it that have almost munched their way through the housing, so that one is junk. There are little windows on the carrier that show you how worn the cones are. If the window is entirely obstructed, the cones are bottomed out. If there is still a little space visible, then the limited slip can likely be repaired with the existing parts, and may even still be operational. Another thing to check is the gears. Check for pitting on the outer portions of the gear tooth face. Bad gear sets will have cratering and pitting in that area as the gears wear and break through the surface treatment.

If you do it through 9bolt.com with the existing rear, the final cost will probably be approaching that of a new aftermarket rear of greater strength like the 12-bolt. You will also have the problem of having a rare setup that doesnt have many parts available for it in the future when something takes a dump.

just for your info? http://motors.shop.ebay.com/__?_from...warner&_sacat= 9 bolt parts can still be had with a little effort, If you want to stick with 9 bolt products, don't let anyone discourage you, they are a good rear end and will take alot of abuse. Here is some more info; http://mpikas.blogspot.com/2008/03/r...rner-cone.html along with this; https://www.thirdgen.org/bw_9-bolt_cone_repair

So dimented,
you do not recommend keeping the 9 bolt 2.77's. But i would like to know what you would recommend replacing it with? Mine is pretty much munched also due to lack of knowledge about the wear matinence. Id say that they are rubbing at least, not sure if they are fixable, or even how you do go about fixing them if there is little clearance. Shimming? grinding? how does that go?

I can see the yukon kit going for about $229.99, but i do realize that you need your cones to be in good shape in order to rebuild it. If i were to take apart the carrier, what would a good cone look like?

About swapping for a 10 bolt assembly for an 89 9 bolt with PBR aluminium calipers, where would i look?

When rebuilding the differential what is the better option - just purchasing the new cones from 9Bolt.com or machining the original ones and then shimming? One of my cones is close to the 1mm minimum (1.25mm) clearance and the other is 1.75mm (based on 9bolt.com recommendations). Since I'm going ahead and rebuilding the rest of my axle I might as well get everything up to spec.

I believe the original rear end will be very important to the value of these cars as time goes on - in particular since the 9 bolt was found in most of the HP versions and is getting harder to find parts for so they are being abandoned. The fact of originality affecting the value has been true for every specialty car ever produced. I've checked, your at a minimum of $2000.00 for a 9" and over $2300 for a 12 bolt.

If you are going for a complete rebuild, I would go with new cones, They are a little over sized, so if your carrier is a little worn, you will be in better shape with the new one's.

Sure, go for the cones.... see this post right below yours.

https://www.thirdgen.org/forums/tran...olt-cones.html

Maybe if you're lucky, your e-mails won't bounce.

Well here's what i did last spring. Bought a used 9 bolt 3.08 rear from a salvage yard for $380. 3.70 nitro ring and pinion for $175 and a master rebuild kit for $160 from justdifferentials.com. 2 new 9 bolt cones $170, I saved my 3.27 rear because it is a 45,000 mi rearend in good shape. I now have a 3.70 9 bolt rebuilt for under $900. I'm sure you could do the same with a 10 bolt, but i didn't want a 10 bolt. Now if you deduct the $380 for the rear, you have a rebuilt for $520. Not bad for a stronger rear than a 10 bolt. As noted before, my original rear has 45,000 on it and still has alot of posi left in it. I dont know what the life expectancy is on a posi, but i don't suspect their made to wear out real soon.

Thanks for the opinion on the cones - I went ahead and ordered two new ones from 9bolt.com. Looking at the post on another member's experience with the new cones I may be looking at doing some machine work on my diff..

Red Rock - great idea and excellent point on building what you want for a great price. Did you do all the work yourself?

My 9-bolt has 55K miles and it is close to wearing out one of the cones and it has not been abused in any way (careful older 1st owner). I would be checking them at 50-60K just to be sure. I wonder if the lube had been changed regularly if it would add to the life of this posi.?

Yes i did the rebuild myself. I had a local machine shop mill down the bottom of each carrier housing flush on the bottom, he charged me $10. I would guess that changing the grease would benifit the life expectancy making sure you also add the additive for posi rears. I had the cover off of my original rear to change the grease, and they look to be about half worn.