Does anyone know how much torque a stock 7.5 inch third gen rear end will take? What about a fourth gen?

 

I'm not sure about specific numbers, but the 4th gen rears are not stronger then the thirdgen rears, they are the same inside. Only advantage of going to a 4th gen rear is better brakes and newer parts.

 

From what I understand, the thirdgen rears are not very strong. If they are the same as the fourth gens, I got something wrong. reason being is that I've seen fourth gen cars running low and mid 11s with the stock rear. Where am I wrong?

 

4th gen rears have better posi units. newer style i believe. and you are right, a 4th gen rear will stand up to multiple 11 second passes easily, ive seen it first hand.

 

There are things you can do to these rears to make them hold up a little better. A girdle will help control flex in the case and keep the gears in line under load. Fact is that the rears use the same size ring gear, so they'll only take so much power. The guys over on camaroz28.com and ls1.com go thru alot of rear ends running those times. Lots of them upgrade to 12 bolts as well.

 

I am planning on putting together a 375 hp, 400 ft lbs of torque motor, and taking out the 305 tbi I have now. I want to have a reliable car though, or at least as close to reliable as I can. I was thinking of getting a fourth gen rear end for several reasons. 1) they come with posi traction(atleast some of them) 2) I want a 3.42 gear ratio (they come with that too) 3) rear disc brakes 4) relatively cheap at junkyards 5) I thought it would hold up OK. As far as transmissions go, I wanted to replace the 700r4 with a T56. I'm pretty sure that tranny will take the abuse. Do you guys think this combination will work? I'm having second thoughts about the rear end if you guys say its the same as the stock third gen.

 

anyone?

 

Keep in mind that a manual tranny is harder on the rear-end than an automatic. A manual will 'shock' the rear harder. Also, do you plan on running slicks? 3rd gen rear ends are just as strong in most cases. It's hard to compare the two since most 3rd gens have more miles(and abuse) than 4th gens. They don't have a magical 'break' torque number--some will break at 300 ftlbs, some not tell 500 plus.

 

Given the fact that the only alternatives to a 10 bolt in these cars cost around $2000, I'd say go with the 4th gen rear end. You can get a 342 posi one complete with brakes from speed automotive for $300. I just today recieved the one i got from them, I'm going to be putting it behind a motor with ~400 lbft, and I'm not overly worried about it breaking. Theres tons of guys over on camaroz28.com and ls1.com that upgrade to 12 bolts and sell their old rears cheap without brakes. You could probably go through 10 of these rears before paying for a 12 bolt or a 9"

 

I think its great that I could upgrade my rear from 2.73 to 3.42 gears, from drums to disc, and get posi traction as well for $300, even if it will not hold any more power. The one thing that I don't want to do though is to have to replace/repair it constantly.
I'm not gonna be running slicks, as this car is my daily driver. I want to keep from going to huge tires, so I can avoid driveline breakage with wheelspin. by the way, cfabe, let me know what problems you run into if any. I'm not sure about how the brake lines line up and how the car looks with the rear tires 1.5" out.

 

Well, I'm using 4th gen wheels so the tire centerline will be in the same place. I know I'm going to have to get creative with the brake lines because my car has sae fittings and the new rear is metric. I had to cut my line to get the old rear out because the nut was too rusty, so I'm probably going to flare the line on there and put on a metric connector, and then make a little jumper line to the rubber hose. Theres alot of conflicting information on what prop valve to use with the 4th gen rear setup, I'll let you know what i figure out when i get that far.

 

Thanks for your help guys. cfabe, do the brake lines go to the LT1 brakes in the same position as the thirdgens? By the way, what year is your car? I have a 92 and when I replaced the wheel cylinders in the back, the brake line connected with a 10mm fitting. Is this what you are talking about?

 

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That's not true. There is the Borg Warner 9 bolt that is a direct bolt in. It can be built for approximately 1/2 the cost of a 9 inch or 12 bolt and will handle most street (street/strip) cars.

Miles
www.9bolt.com

 

The 9 bolt is another alternative, however it has the downside that it was only offered in these cars one year so parts tend to be hard to find (you need to order them from austrailia or hook up with one of the guys that imports parts for them). Also, theres a more limited choice of gears i believe. Its stronger, but I'm really not sure by what degree.

92, If you get a 4th gen rear without ASR (traction control) the brake hose will come off the rear in about the same place as a thirdgen rear (just to the drivers side of the differential). GM switched fomr sae fittings to metric in 84 I believe, so on my car I'm going to have to cut the fitting off of the end of the under car brake line and re-flare it with the proper metric fitting to go into the hose that came with my rear end. the hose looks like it will fit into the same bracket. On your 92, I'm pretty sure the brake line will just bolt up, because you should be using metric connectors like the 4th gens. If you do end up getting an ASR rear end you'll have to buy or fabricate new brake lines for the axle and get the proper hose.

 

Sorry if this sounds like a stupid qestion, but how can you tell if the rear end came from a car w/ traction control. I don't have the slightest clue how that system works, as I've never worked on a car with it. By the way, cfabe, hows the swap coming along?

 

part of being ablt to tell is if both wheels have a relotor wheel on them, if they do then tada it is if no then it probably isnt

 

reluctor..sorry somethin like that

 

Yea, the cars without traction control have single channel rear brakes (just one line running down the underside of the car that splits at the exle) and just have one abs sensor in the differential. I've never seen the traction control setup but I imagine it has a sensor on each wheel and the brake lines wont have the tee in them.