Steven6282

I'm looking at reworking my rear end as the next project on my car. I'm going to stay with the 10 bolt, just going to add a series 3 posi (currently is open), and upgrade to 28 spline axles and 3.73 gears while doing it. (Currently have 3.23 I think, and 26 spline axles).

I was looking on Summit, and the summit branded stuff is a good deal cheaper than others.

Gears:
http://www.summitracing.com/parts/SUM-741011/

Axles:
http://www.summitracing.com/parts/SUM-700118/

One thing I question on the axles, the part says it's for 7.625 in, where as mine is 7.5. However I didn't think that would matter on the axles if the length was correct? The length on the Summit axles is 30.310 where it is 30.312 on these Moser's:

http://www.summitracing.com/parts/MSR-A102804/

The summit axles though are 60 dollars cheaper and comes with new seals, bearings, and studs where as the Moser doesn't come with any thing extra.

So if the summit branded stuff was good quality and those summit branded axles would work in my rear end, I think I might would rather go with them.

EDIT:
Oh yeah while I'm posting everything else this is the posi I was going to go with:

http://www.summitracing.com/parts/DTL-912A317/

It was suggested to me as a good high end posi, better than the stock eaton, or auburn units. I don't know how true that is, but I welcome suggestions on it too.

sofakingdom

iTrader: (1)

30.3125 = 30-5/16 which is the "nominal" length... .0025 is about the thickness of a piece of high-quality laser printer paper, meaning, the difference between a cold axle and a hot one is greater. Totally irrelevant.

Most Summit-brand parts (there are exceptions of course) aren't some kind of crap, although they're not usually "top of the line" either. In the case of gears, I'd expect something like AA&M (Motive), or the stock replacement (NOT "Evolution") Superior ones.

Steven6282

So, does that mean those axles would fit in my 7.5 in 10 bolt even though it says 7.625 in in the item description? I noticed the detroit locker posi I was looking at shows applications for both 7.5 and 7.625 on it, so I'm guessing the answer to my question is yes. I just want to confirm before I order anything.

As for the quality, I don't think I need top of the line parts. I'm only going to be pushing max 300 rwhp and maybe 400 lbs of torque. And it wont be on any drag runs, mostly just autocross / pdx type stuff. As long as it's not complete junk I'm thinking I should be ok. Just trying to confirm that is the case here.

TheMonster

A lot of summit's parts are manufactured through other companies, example:Summit shorty headers = Flowtech

YMMV, but I plan on buying those same exact gears soon.

I wouldn't compare summit axles to Moser though!

Steven6282

Only thing I'm comparing is the price and the fact that the summit axles are not only 60 dollars cheaper but come with another 70ish+ dollars worth of parts (seals, bearings, and studs). Making them effectively 130 dollars cheaper.

I know Moser are most likely stronger, but if the Summits are strong enough for my application, there is no reason to spend that much more on them.

Also just to add, I was reading another post while trying to figure out this 7.5 vs 7.625 thing, and it seems I may have a 7.625 in mine right now. Found one post saying that they switched to 7.625 in 86 which is what year mine is. I'm not sure how to find out for sure?

But also it seems this 7.5 vs 7.625 is all referring to the carrier size. The Detroit locker posi I'm looking at is what is considered the carrier correct? In it's description it says it's 7.5 in, but under the applications shows applications for 7.625 in as well. It even shows up if I drill down using GM 7.625in as an option along with Chevrolet and using the year 1992 to make sure I'm looking at 28 spline stuff.

This is the only detroit locker that says 7.625 in the description, but I can't figure out what is different about it other than that to make it cost 180 dollars more than the first one I linked.

http://www.summitracing.com/parts/DTL-162C59A/

EDIT:
Running into the typical problem with the internet and that is cannot find a consistent answer on this stuff. Seems like 7.625 axles will work with a 7.5 in carrier and vice versa. But I found other things saying that a rear end that came with 26 spline axles will not accommodate 28 spline axles because the hole is to small. Is this just a hole in the side of the differential? Or is this the hole in the side of the center of the rear end itself? Can someone clarify for me what exactly is the "carrier"? Is the differential the carrier, or is the carrier the part of the axle that everything sits into?

This all is so confusing and with so much differing information I can't seem to figure it out.

Basically I guess it boils down to three questions:
Will those 3 things I linked in my first post work together?
Will it all fit in my 10 bolt rear end?
Is the quality of it all good enough for 300 rwhp, 400 ft/lbs of torque max, doing autocross / pdx type runs on it?

Thanks

TheMonster

I understand, just talking about the quality of the actual axles.

https://www.thirdgen.org/forums/tran...olt-7-5-a.html

Read post #2, axles may not work?
Also read post #8/#9 about when they switched sizes.

Also the 7.5 vs 7.625 is just the gear size, the gears will work in both from what I remember.

8t2 z-chev

if your axle is '86,it should be 7.625 ring gear-'85 is
when the change to 7.625 occured,the 3.42 gears in my
car came from an'85 v6 camaro 7.625 ring gear.
i don't think there is any difference between f-bod 7.5
and 7.625 anyway...I'D be real leery of cheap axles-
probably chinese low grade scrap iron junk...

Steven6282

Yeah I read that post already. It's confusing because I can't tell which parts they are talking about. I don't understand which is the housing which is the carrier, what has to be able to accept 7.625 or 7.5.... With the detroit truetrac I'm looking at showing applications for 7.5 and 7.625, it is all very confusing.

I need someone that knows for sure what they are saying, to say definitively one way or the other whether these parts will all play well together in my 86 10 bolt rear end.

8t2 z-chev

the carrier is the part the ring gear bolts to and
contains the spider gears and posi if equipped-
Housing is just the big cast iron gearcase the axle tubes
are pressed/welded into.

Steven6282

And what about everything else? lol Sorry but all of this is really confusing for someone that is coming into this not knowing squat and just wants to upgrade their rear end and add limited slip.

I think from reading other places the consensus is the Truetrac is better than a full locker for autocross type applications. And that GM 7.5 in Truetrac is the only one I can find. It comes up in searches for 7.625 as well as 7.5.

To add to the confusion I found some moser axles that list that they fit 7.625 and 7.5 in. Yet they also had individual ones saying only one or the other.

The gears seem to be interchangeable. Almost all the ones I look at say 7.5 / 7.625.

If I understand the 7.5 vs 7.625 correctly from what I have been able to find on it, it's just the overall diameter of the ring. If that is the case I don't see why it would matter which size you have when it comes to the axles as long as the axle spline count and length matches that of the carrier and axle tubes. But it's entirely possible that I'm misunderstanding something.

I'm about to head to bed for tonight, can't seem to find any solid answers telling me one way or the other on the internet tonight. Hopefully someone can respond to this tonight and fully explain it, or I can find someone that I can call tomorrow to figure it out.

sofakingdom

iTrader: (1)

28-spline axles won't fit into a 26-spline carrier, for reasons beyond the # of splines... specifically, they're too big to fit through the holes in the sides of the carrier.

As I have posted in the past, the True-trac replaces THE GUTS of the carrier, and therefore will only fit inside the carrier it's designed for. It will only fit an "open" carrier for example, won't go into an Auburn or Gov-Lock posi. Plus, early carriers are different inside from later ones, even though the gears bolt to them interchangeably. You gotta get the right True-trac for whichever carrier you have.

So: you can't take a 28-spline one and stick it into an early carrier that's the wrong size for it; not only will the axles not go into the carrier, but neither will the True-trac.

However, you can get a later-model carrier, and it will go RIGHT INTO your housing; and then you can use a 28-spline True-trac and 28-spline axles.

And yes, the 2 size designations of gears are COMPLETELY interchangeable. In fact there are AFAIK no 7.5" ones madde any more, they're ACTUALLY all 7.625".

I'd recommend these axles right here. http://www.summitracing.com/parts/SAG-EV10-4/ They're BETTER than Moser, because Moser and the other "custom" makers, in order to hold their lead time down, use HARDER metal but DON'T heat-treat it farther after addign the splines, and the splines are CUT rather than ROLLED; whereas, these are splined BEFORE heat treating, and the splines are ROLLED rather than CUT, and the metal is then HARDER after heat-treating than the other (heat-treating takes several weeks to do right, which is where the lead-time issue comes into play). While Moser is a perfectly good company and product for situations that require something different from stock, they other "custom" axle makers are best left to applications requiring actual "custom" axles, while these are better for situations where they are STOCK configuration (length, dia, bearings, splines, flange, etc.).

Note that the Superior kits also come with new bearings, seals, and studs... that $60 worth, or whatever it is, of stuff, that you DON'T have to buy separately.

Needless to say, you're going to be pounding about $750 OR MORE into this rear; not alot of sense in doing all that to some crappy drum-brake, or Saginaw disc-brake, rear. Since, like engines, the CORE (the old wore-out thing you're rebuilding and/or upgrading) is THE CHEEEEEEEEPEST part of the whole project, might as well start out with the best one you can find. Go get a 90-92 disc brake rear, or an 4th gen; and if you find a 4th gen one out of a 98-up TransAm or Z28, you get NOT ONLY the 28 spline axles and the better posi such that YOU DON'T HAVE TO BUY THAT AT ALL in the first place, but also, you get the better brakes.

Steven6282

Now see you are confusing me even more lol.

What is the CARRIER? I've been told that the differential is the carrier. The Detroit Truetrac is even listed under the category "Differential Carriers" on summit racing. You talk about the truetrac as if it has to go inside of some other carrier, but I was under the impression that the only thing it has to go inside of is the housing? Even by 8t2 z-chev's definition:

The ring gear would bolt to the Truetrac, would it not?

Other than the disc brakes what would make a 90 - 92 housing better than my 86 housing? They are both 10 bolt 7.625in housings as far as I can tell. If I replaced all the guts in my 86 10 bolt with 28 spline stuff, it would be better than a used 90 to 92 with worn out 28 spline stuff. I'd only be lacking disc brakes.

Swapping to disc brakes has an entire other set of problems with it that I will get to eventually but do not want to get into right now with all the gearing and stuff too. Changing parking brake lines, adding a proportioning valve and all of that stuff.

Granted yes, if I could find a 10 bolt 90 to 92 rear end with a good posi, good gears in the size I want (at least 3.73 although I'm entertaining 4.10 as well), and disc brakes for fairly cheap then I might would get it and use it for now. But the chances of me finding one in good condition for cheap is slim, I've looked previously. Most of the time the posi is worn out in these old units meaning I'd have to replace the posi and gears anyway, and also most of the time they don't have the gear size that I want in them. Now if I could find a 10 bolt with disc brakes with known bad posi or gears for really cheap, I might would buy it and put all the new stuff in it then swap the rears, but it'd have to be like maybe 50 or 100 dollars for me to consider doing that right now. I can get a brand new disc brake swap kit for 250 dollars, so I'd rather do that than spend 150 or 200 dollars on a used disc brake setup and still have to buy some stuff to complete the swap into my car.

I'm not even considering 4th gen rear ends. I want to keep my iroc wheels and do not want them sticking out an extra 2+ inches on either side.

And also I'm still left scratching my head as to whether or not the 7.5 or 7.625in really matters on the axle shafts.

JamesC

iTrader: (5)

No. Look up Moser part #A102604 on Summit and you'll see that the axles fit both.

JamesC

SCCAjunkie

To try to get straightforward answers- This is my understanding, and someone correct me if I'm wrong.

7.5 and 7.625 are interchangeable numbers essentially.
The spline count from axle to diff must match.

Carrier is the thing inside that "carries" the gears, whether it be open or limited slip (or posi).

Posi is technically a type of limited slip, much like Kleenex is a type of tissue. There are other kinds of limited slip units, but many people will call it a "posi" due to brand recognition.

The differential is the whole carrier and gear assembly that allows (or doesn't allow) differences in rotation between the two axles.

What sofa was saying is that if you get an insert-type diff, it was meant to go in your carrier (metal gear-holder), and that wouldn't allow you to use different axles. If, however, you get a whole new carrier, like the locker unit you linked to, you'd be fine. The true-tracs that Summit has listed appear to be the whole unit (stuff like the Powertrax is an insert).

Bottom line-
Buy all the parts you originally listed, and they should fit.


On a whole nother level, I'd suggest that a locker may not be the best for AutoX/PDX/etc. (nice to see someone use the PDX moniker, by the way!). You can often find the stock differential from a 4th gen (not the whole rear, just the diff), which is a Torsen-type unit. It has a much more progressive torque biasing quality versus a locker, and is more consistent and less wear than a clutch-type. SLP used to sell them cheep, but I don't think they do any more...

Steven6282

Thanks for clearing that up SCCAjunkie,

Just one additional question. I though that was the point of a Detroit Truetrac, that it wasn't an actual locker (they have a separate product labeled as a Detroit Locker).

The way I understand from reading about them the TrueTrac behaves like an open differential until one wheel starts to slip and then the gears cause torque to get sent to the the other wheel with traction. The locker on the other hand is always locked on, but will allow the wheels to turn at different rates when needed. This is why I've seen people say that the TrueTrac is better than the Locker for autox, because the Locker could cause high speed cornering issues and make it easier for the rear end to get out from under you. From my understanding the locker is geared more toward drag racing and 4x4 type applications.

Also with the TrueTrac having some sort of gearing system, no cones, or clutches or anything like that, it's supposed to be very hard to wear out (at least from what I read).

Anyway, that is the only reason I was considering the TrueTrac over an Auburn Posi unit, because I thought it was basically the same as a torsen type unit but better.

sofakingdom

iTrader: (1)

These are "carriers"....



2 series WITH a ring gear on it on the left, 3 series WITHOUT a ring on the right.

Imagine what's inside a rear end. Take out the axles, ring & pinion gears, fluid, and the caps that hold everything in. What's left, is the carrier.

SCCAjunkie

Yes, you are correct, and that is the type I was referring to. When I clicked on it at work, all I could see was the title, not a description (stupid weird proxy server we have). I didn't realize that TrueTrac was the Detroit/Eaton version of the Torsen.

One minor word of warning- It is still possible to spin one tire with this diff. The likelihood of doing it on a road course is slim, but under autocross conditions, you might experience it. One good thing though, is that it will teach you not to rely on the diff as a crutch... This diff has fallen under more criticism lately by the "serious racer" due to this issue, but I continue to stand by it as the best choice for entry-to-mid-level drivers and cars.

Steven6282

Hrmm, well the question is, if I spin one tire with this is it still diverting sufficient torque to the other tire to make up for it? That is the problem with my open differential right now, when one tire is spinning, the other isn't doing anything to make up for it. So I really have to baby the gas coming out of corners to keep from loosing traction.

What type of posi unit would prevent any spins at all? A full locker I'm guessing?

jmd

iTrader: (4)

A Lock-Right installs into an open carrier.
An Eaton Detroit True-trac is a torsen-type gear-bias carrier.

Torsen makes some diffs. in different bias levels. Their entry level T1 is gear bias only. They make others that are T-2R (and other) that are a friction (cone or clutch) assembly that pre-loads the gear-bias section. I don't know if Moser makes their Wavetrac (friction pre-loaded gear-bias diff.) for the 7.5" 10 bolt. Which ones are less or more aggressive than the Detroit True-trac, I don't know. For your intended use of the car, I wouldn't worry about it; just order the 3-series 28 spline true-trac and enjoy it.

The positives of getting a 4th gen complete axle assy. with Torsen already in it (assuming it's not a 2.73 ratio) would give you all the upgrades you want for cheaper. You are choosing to keep stock width and new parts, which isn't a bad decision at all for a car you're going to keep and drive for a while.

One thing a friend ran into when he rebuilt his 7.5" 10 bolt was new axles (major name brand) and an SLP new take-out Torsen diff. The axles were fine, but the short section just inboard of the c-clip was larger than stock and needed milled or tapered to clear the paddle piece of the Torsen unit, so the c-clips could be installed and the center paddle then installed.

91 1LE

iTrader: (1)

I had this same problem with the Alloy USA branded axles (and I'm assuming they make the Summit axles as well). They were quite a bit too long after the c-clip and required a lot of grinding. And the studs they included were 1/2-20, not the 12-1.5 metric studs our cars require.

SCCAjunkie

The only type of diff that prevents any spinning is not a diff at all- it's a spool (locks both axles to the carrier, and thus, the ring gear rotations).

A full locker comes right behind that, with the manual locking units acting like a spool when locked, and an open diff when not. The dog-types are next, which allow some small amount of slip until the dogs catch, then it's locked until it unloads.

As jmd mentioned, there are Torsens out there (T2R) that are pre-loaded to reduce the one wheel spin issue.

Without going into Torsen theory, essentially the helical gears use torque differential to bias torque delivery based on a ratio that's engineered into the unit. If the bias ratio is 2:1, and your wheel with the least traction get get enough grip to put down 50 ft.lb., your better tire will see 100 ft.lb., which is awesome. The problem is, if your one tire is on glare ice (or it's completely lifted on the inside of a turn), you will be able to apply 0 ft.lb., and 0 times any multiplier is still 0. You can combat this by never unloading the tire (this is best) or by applying slight brake pressure (works great off-roading, but not racing). The T2R unit adds clutches to pre-load the unit like a clutch-type diff in those situations, reducing the likelihood of it happening, but not eliminating it. I run a T2R in my car and can confirm that it's possible to spin one, but I have to actually try to do it.

Honestly, I find that the stock T2 (non-preload) type diff is awesome for those with less experience, because, as I said above, it will not mask the fact that you unloaded a drive wheel. This is VERY important information to know, and I can tell you that I've had to develop a real "feel" for my diff. Also, the non-preload type gives you more torque application as the surface will allow, so it's more difficult (though certainly not impossible) to do something silly and go for an unintended ride...

Steven6282

How exactly do you unload or avoid unloading a drive wheel? I'm sure I've probably done this but have never heard it termed like that so not sure what it is.

I don't want to spend 400 dollars on a posi and it not do anything to help my current situation. I mean when the one tire starts spinning right now I have to let off the gas almost all the way to regain traction on it, which is killing me coming out of tight corners especially when there are straight shots after them. The way you are describing this unit, it sounds like I'm still going to be getting very little torque to the other wheel in this situation.

Right now the only way I've found to combat it some is to slide my rear end around in order to be coming out of the corner more straight and able to get on the gas a little quicker. I know I could improve my times if I didn't have to do that though and could get on the gas when coming out of the turn instead of waiting for the rear end to straighten out behind me.

Perhaps I'd be better off looking for a T2R style differential? Do you have any links to one that will fit a 3rd gen rear end? I talked with Sam Strano before and he told me he didn't sale a torsen to fit my car because when he did before it had major wear issues. He had suggested the Auburn Racer's differential, but not sure what that one is either or where I could order one. Just looking back at his email, he also told me 3.73 gears were to short for a T5, which is what I had planned to use, but I'm also probably going to be swapping in a T56... so I'm not really sure what is the best route there lol.

SCCAjunkie

OK, let me start by saying that I'm not an expert on 3rd gens, though I have raced several in various types of events (road racing, hillclimb, track/club trials) and logged many PDX/HPDE laps in them. Much of this discussion at this point, however, extends across any platform.

The Torsen will absolutely help over an open diff (or a worn limited slip of other types), as if you have ANY traction at the inside wheel, the torque biasing will kick in. If you use the T2 style (non-preload) diff, you *may* still experience inside wheel spin on some very tight corners, particularly at autocross. The major difference will be that instead of laying off the throttle completely and then only being able to feed in what one tire can handle, you'll be able to breathe off and find inside rear grip, then immediately roll back into it and modulate as traction allows. I'm not saying this diff won't help you, I just have seen too many guys that I race with purchase it with unrealistic expectations, and then curse and swear when they experience the old inside-lift-and-spin in the tight turns at the hillclimbs around here.

The inside-lift scenario is the product of several issues- chassis setup, suspension setup, and driving style are the major points. I'd need to know your whole suspension setup to give real opinions as to reasons why you might have issues, but before that I'd suggest you hang out in the suspension forums and listen to guys like Pablo and Dean that are more qualified than me to offer platform-specific advice. As far as driving style, I'd be happy to chat about it. With my old car (90 Formula) with a non-preload T2, it was all about apexing those straightway leading turns VERY late. I found though that I loved being able to maximize my exits because I had confidence that my back end was planted, but still I could put down all the power I had, which wouldn't have been possible with an open (or worn) diff.

I know that a T2R is available for the 10-bolt, as I have one. Unfortunately, I have no info on it because it came with the car. I believe it might be the SLP-spec'd unit, but even so, I'm sure they had them made by someone and that they're still available somewhere. I'd suggest that it's the best for what you're asking, but finding one doesn't seem to be easy (I've been looking as I type this).

As for gears, what 5th gear does your T5 have? I have the "short" 5th (.73 I believe) and I'd concur that 3.42s are great, unless you have a LOT of RPM to play with. I spent some time in a 500-ish hp 84 Camaro with a T5 (.73) and 3.73s, but it revved freely to 7000 rpm. My current setup at 300-ish hp and about a 5500-6000 redline is very well geared...

Steven6282

I've got a descent suspension set up. Nothing to great, it still needs to be retweaked later on with some better stuff but for now it works really well for me. I've got koni yellows all around, spohn sway bar set, eibach prokit springs, rod end lcas, have replaced all of my bushings, new ball joints on the front, wonder bar, Founder's strut towers, all new steering components except the gear box which has been adjusted so that it is really tight again (it's the sport 2.5 lock to lock gear box). I'll add SFCs eventually, but I'm waiting to see if Founder's is going to make some and how much they charge for them before I pay for UMIs, Founder's is usually a bit cheaper and just as good of quality. I don't have a lot of lean in the corners anymore, like I used to on the worn out stock stuff. I really happy with how it handles right now, it's plenty good enough for me while I'm learning until I get more competitive.

For the gears, I have no clue what my 5th gear in my T5 is. All I know is it is the non wc T5. I'm just worried about lower gears running out to fast if I swapping in a T56. I don't want to get stuck having to shift between 2nd and 3rd a lot on the course. Most courses right now I get into 2nd pretty quick and can stay there the entire course. My engine red lines at 5500. I had someone else tell me today that they think a 3.42 gear would be a good gear for me to go to, but if the tech data on the main site is correct, I've already got 3.23 (unless it's a Sport Coupe, but I don't know of anyway to find out for sure if it was a Sport Coupe or a Z28 model), that would be a very small change.

I dunno, I'm gonna have to think on it more and try to do some more research before I buy anything. If I can find a 90 to 92 rear end with disc brakes and working posi in it, I think I'm gonna pick one of those up until I decide for sure what I want to do. Just can't seem to find any anywhere close to my area for sale with disc brakes If it weren't for the tires poking out the side I've got a 97 trans am rear end with posi sitting under my 84 camaro in my back yard lol.