ok whats the deal is the 4th gen rear the same as ours but longer or does it have beefier components? if is not beefier then why do some people swap them into their 3rd gens? i have had guys on a 4th gen board tell me they are the same and from other sources that they are stronger whats the deal?

 

They are identical to the 90-92 rears in every way as far as strength. The only difference between them and the 88-back 10-bolts, where strength is concerned, is the smaller axles in teh old rears.

The reasons people swap them in are (1) they are far more plentiful than 90-92s; (2) they often come with better gear ratios than the rev-challenged TPI and TBI cars did; and (3) they have better brakes.

 

The 4th gen ring gear is 7 5/8" while most of the third gen rears are 7.5". That alone is a strength improvement. Also the 4th gen gears are metalurgically stronger. GM didn't want to pay American Axle and Mfg, the supplier for the rears, to tool for a larger axle to cope with the loads from the Lt1 and Ls1. So AAM incorporated shot peening and better heat treating to the gear mfg process. The 7 5/8" rear axle in the f-car is one of the most power dense axles you'll find in any car in the world, it just has a size disadvantage.

 

No, the third gen 10 bolt rear is also 7 5/8

 

gm just wanted to confuse us by calling the same part by 2 names, 7.5 and 7.62.

 

They are identical. The same gears have been in use since 78. They have come in A, B, G, and F cars; and S trucks, Astro vans and maybe some other car lines I can't think of.

Look in any book, AA&M (Motive) or Superior or Dana or whoever, they're all the same, from 78 up. They didn't change anything about what's inside the rear housing when they changed the car body; not the F car body, or the S truck body, etc. etc.

 

As far as interchangeablity maybe. Just because the parts bolt together the same doesn't mean that they are the same parts. How parts are manufactured can change the strength drastically. The 4th gen parts will be slightly stronger but in my opinion that alone is not a reason to change to a 4th gen. If you want more strength go to something bigger. Check the original part numbers for a latemodel GM S-10 truck gearset vs an F-car gearset and see if they are the same. The F-car gearsets were shot-peened for more strength. That wasn't necessary for the S-10, so they skipped it.

And for the record my 87 had a 7.5 originally.

 

truth:


more of them came with a posi. therefore when looking for a posi swap, you can find them easier.

the posi is a diff style and is slightly better then the older style. somehow, when talking about gears, and axle splines and everything else, people tend to forget that its a diff style posi.... the posi itself will bolt into your 3rdgen rear too, so you can upgrade if you want...


they have better brakes. and you are more likely to find a disc rear.

most have better gear ratios..



so you are more likely to find a good ratio, posi disc 4thgen rear then 3rdgen...... thats all.

i want a 98+ 4thgen disc rear mearly because it would go perfect with the 98+ brakes im putting on the front.

 

You guys forget that the 4th gen rears fit the newer rims... With a 3rd gen rear you would need a spacer adapter to fit the newer wheels... I wouldnt trust putting a spacer up to the power some people want to produce. So a 4th gen rear is the way to go.

 

What do you mean "newer" wheels? If by 4th gen, you mean newer then ok, but several aftermarket companies make "newer" wheels for our cars that IMO look much better than 4th gen rims. BTW, longer means weaker, shorter means stronger. For example, take a pencil, and break it in half, pretty easy right? Now take a half and break than in half, and so on and so forth. Get's harder right? Therefor, third gen rear= stronger and 4th gen is not the way to go, unless ofcourse you want the "newer" 4th gen rims. But if you want 4th gen stuff, get a 4th gen. Just my opinion though.

 

By newer rims I meant newer camaro rims so yes the 4th gen rims... Some people just like the way they look, like the Z06 rims are getting popular. Hey dont look at me tho, I run a 3rd gen 9 bolt. So I am all for rims to fit my car.

 

also, for that newer rims comment:


there seems to be ALOT more rims out there with 4thgen backspacing then 3rdgen.

so while you can always get spacers for 3rdgens and be able to run both, if you are planning on getting wheels that require spacers, it may be cheaper to get the 4thgen rear when you swap axles, then the rims with only 2 spacers.

 

I put the 4th gen rear on my car since I have 4th gen wheels and I wanted the bigger brakes.

9bolts are stronger, btw.

 

To add a hair more to what RB83L69 said, I agree the gears are the same, the only appreciable difference that some will say that adds to the strength are the slight changes to the differential (depending on who GM bought them from).
Somebody can clarify, but GM has not always used the oem Auburn in the earlier 3rd gen cars. Earlier 3rd gen cars did have some higher failure rates. Obviously some of this was due to the 26 vs. 28 spline designs. by the latter 4th gen years, the change to the oem Torsens had occured. Zexel/Gleason (mfr of the Torsen) has a "white paper" I had a copy of that claims approximately a 10-15% increase in strength over earlier units. I don't recall any other details fo the tests in the white paper.

See the post link for a hair more on the progression of the history between the oem Auburn, oem Torsen, HD Torsen, and the SLP spec Auburn.

https://www.thirdgen.org/techbb2/sho...48#post1488348

 

Yes, 9 bolt rears are stronger, but are rare. They do not make
them anymore. Even if they are, 10 bolts in 4th gens put
up with about 320 rear wheel hp all the time ( 1998-2002).

 

I am hoping my 9 bolt will handle up to 400-500 rwhp.

 

hehehe not for long they dont! Slap on some DR's and a driver that loves speed and that 10 bolt is set for destruction. Most LS1 drivers will crap there 10 bolts after minor track use.... Some dont even wana go through the hassle and sell there rears for 12 bolts... hence the influx of 4th gen rears. 4th gen rears are marginaly stronger, but not enuff to hold up to over 350 to the wheels... GM should of made a stronger rear end with these cars...

 

you should hope about $2,500 falls into your lap for a 12 bolt soon too...

 

Well, my brothers car only puts down 280rwhp and he's snapped 12 gear sets.
Here are latest 3,

 

I didn't see it posted here, but the 4th gen rear axle is exactly 3 inches wider overall than a 3rd gen rear.

And if you have blown 12 diffs with 280 RWHP there is something drastically wrong with something in that diff/case/setup(s) or the driver is being careless - IMO.

 

it was with 3 different rear ends. They usually last for a few m onths before they break.

 

280rwhp sounds about right if hes launching the car at high rpms and has sticky tires. Blowing 12 diffs... thats just dumb... after 5 you think you would learn!!! save up the money and get a dana 60 or something! Torque has a lot more to do with snapping the axle then hp. 280hp, but 400ft/lbs will snap 12 diffs.

 

It's a 6 speed LT1, don't remember the torque.
It was easier to change the gears every so often than it was to buy a 12 bolt since the gears were only $140. He's going with an Auto so it should be a bit easier on the gears.

 

its 4 inches wider overall.

he didnt say the TQ.. and that effects the launch alot. a low HP torquey motor will shread a rear just as easily as a 500hp racer.

sticky tires kill 10bolts.. peroid.

and before i even clicked page two, i though, he probly has a manual... a auto is much softer on the rear.

 

Well I measured mine before I put it in and there was exactly a 3 inch difference from the 87 9 bolt that I took out and the 96 10 bolt on its way in...

And.... if you do the conversion on the backspacing of 4th gen wheels to thirdgen wheels (factory stuff), 3 inches would be the most correct. Example:

- 3rd gen rear 16 inch wheels have a 16 mm offset which equals approximately .625" .
- 4th gen 16 inch wheels (they have the same offset front and rear) have a 55mm offset which equals approximately 2.1875" .

Math:

2 x 2.1875 = 4.375.
2 x .625 = 1.25.
4.375 - 1.25 = 3.125

Much closer to the 3" actual that I measured - and there are numerous things that could explain that extra 1/8th of an inch (including my measuring abilities ). But the chassis are, for rear axle purposes, identical - LCA, TA, and PHR bracketry proves that.

As posted above, and IMO, it is still a bit self defeating to be blowing rears up that often and that is my point. But if that was with several cases then I would be inclined to investigate the setup procedures I was using.

just my $.02

 

Gears were setup by 3 different people.
Doesn't matter what you do, the 10 bolt will break, just a matter of when.

TQ at the wheels was 313.

 

You're just reposting what you've heard others say, and have never measured yourself. I measured mine - 85 10 bolt vs 02 10 bolt - difference was exactly 3", like I posted over at CamaroZ28.com

 

Measure an LT1 rear if you have access to one. I have heard that one is wider than the other, can't remember which.
I am referring to the LS1 98-02 and LT1 93-97 rear ends.

 

Well, I guess when I'm done with my car, we will see!
It's only money to me. If I have to convert to a Moser 12 bolt
Chevy rear, than so be it! That's why I'm not converting my
rear drum to Baer rear disc conversion yet. But for now, I
will "gamble" with my modified 10 bolt. I'm sure it will hold
up to 300 rwhp and 340 rhwtrq. I don't drive like a racer all the
time. My friend's 1998 Trans Am has over 50k on it,
and it just dynoed at 355 rwhp/354 rwhtrq ( some mods).
He ALWAYS beats the living F#% out of it! Nothing has
broke yet! I believe that these 10 bolts ( if built right,
with ALL high performance parts) can hold up to 350-380
rwhtrq. IF the entire rear is stock, then NO, it will not.

Bye the way, I hear alot about those 10 bolts blowing up
after you put on drag slicks or radials. I can see that , but
if you only occassionly beat the bag out of it with only
regular street tires, I don't see why it wouldn't hold up.

On another note, how much can a Moser 12 bolt Chevy
rear hold up to??? 700 hp? 800 hp? 800 ft. lbs.?

 

ok... i'll rephase



it moved the wheels almost exactly 2" outward on both sides!





and i got that from measuring the rim distance before and after.



why do we use 2"- 2 1/4" spacers with 4thgen wheels then? shouldnt we be using 1.5" spacers????

 

Most people run 1.25-1.75" spacers on the rear.
I ran 2.25" all the way around on my setup so it would make selling the extra pair easier to someone that needed front spacers.