Rumor about Rear-End, need confirmation.

[drifts14x]

Ok, so I'm probably in the same boat as all of you, I would love a 12-bolt rear-end for my F-Body (95 Trans Am in my case), but I don't want to spend a healthy $2200-2600 on a rear-end for a car I paid $3500 for. So, here's the deal, I read this, and I figured that if anybody knew anything about it, you guys would know.

Possible Redemption for our Cars

With that in mind, how much of a PITA would it be to swap a 7.5 Diff for an 8.5 if that were the case?

This could make for one really good sticky if this proves to be a potential solution.

[78formula78]

well it seems that it would be a solution but you would have to do some work. but your parts wouldn't interchange with that rear end... at least they didn't say it would. so you would need to fabricate spring and shock mounts, and either use the drum brakes on that rear end or buy a new set.

[TraceZ]

How would you attach the torque arm to the differential housing?

[Z Ya Later]

Well, you could always get the GNX rear cover that has the torque arm mount on it. Interesting fact, the G-bodies came with the 8.5" 10-bolt.

[Injuneer]

About the cheapest upgrade you can get is a converted Ford 8.8-inch. There are people making the conversions. Try a "search" on the "Drivetrain" forum on CamaroZ28.com

I thought the GNX had "ears" on the housing for upper control arms, in effect a 4-link rear suspension.

[Z Ya Later]

I thought the GNX had "ears" on the housing for upper control arms, in effect a 4-link rear suspension.

Actually, that's the stock GN rear suspension. For the GNX, they set up the rear quite similar to the F-body rear. Here's some pics...







...and a tech illustration...



...courtesy of Kirban Performance. I wonder how hard it would be to get a G-body 10-bolt working in an F-body...

[Injuneer]

Well, I learned something today.

I wonder if the GNX rear cover is sort of "rare"? Who made it?

[Z Ya Later]

I wonder if the GNX rear cover is sort of "rare"? Who made it?

The original ones, I believe, were made in-house by ASC/McLaren, but I could be wrong. However, Kirban Performance does sell a reproduction unit for $170. Are we starting to get ideas?

[toddwirges]

Are you running drag radials?

The 10 bolt won't just immediately explode if you're on street tires. It may last quite a long time.

Most people agree though, that if you are going running a manual with drag radials or slicks, don't beat around the bush and just go to a 9" and be done with it.

Screwing around with a 12 bolt with a manual and sticky tires is pretty much universally agreed to be a waste of time. They can hold up to autos but not manuals.

[fastTa]

Are you running drag radials?

The 10 bolt won't just immediately explode if you're on street tires. It may last quite a long time.

Most people agree though, that if you are going running a manual with drag radials or slicks, don't beat around the bush and just go to a 9" and be done with it.

Screwing around with a 12 bolt with a manual and sticky tires is pretty much universally agreed to be a waste of time. They can hold up to autos but not manuals.

Kind of a uninformed blanket statement don't you think? I've seen 12 bolts hold up to well over 1,000 HP at the crank with a T-56 and repetitive 4-5k clutch dumps. Especially a spool. It takes much less horsepower to turn a 12 bolt, which equates to more HP to the tire and a faster ride. A 9" is a little overkill unless you are building a dedicated drag car that is going to be creating some serious torque loads.

If all someone cared about is building the most bulletproof driveline available at the sacrifice of WHP and ultimately the car's performance, then go for it. But, most of us hotrodders are out to make our car perform to the best of it's abilities, and under most street car power levels, a 12 bolt is more than sufficient.

[toddwirges]

Kind of a uninformed blanket statement don't you think?

Actually I think it's quite a well-informed blanket statement. But you are entitled to your opinion, as I am mine.

>500HP + T-56 + 12 bolt + drag tires = bad idea

[Z Ya Later]

Actually I think it's quite a well-informed blanket statement. But you are entitled to your opinion, as I am mine.

>500HP + T-56 + 12 bolt + drag tires = bad idea

Yeah, I'm gonna agree with Kev. on this one. I've seen GN's with 8.5" t0-bolts take more abuse then your "equation" there and keep asking for more. The 8.875" 12-bolt is a very strong unit and a great choice for any car not being made into an all-out drag car (trailer-queen). Plus, should you so please, the 12-bolt will still work with the factory ABS and TCS systems, keeping every system working and your insurance down (ABS is a discount ). We have guys here running more than 500 hp and a 10-bolt without any problems whatsoever.

Heck, Kev.'s pointed out on many occasions he's had the factory 10-bolt take 488 RWHP. Not every blanket statement is a good one. But, as you said, you are entitled to your own opinion

[fastTa]

Actually I think it's quite a well-informed blanket statement. But you are entitled to your opinion, as I am mine.

>500HP + T-56 + 12 bolt + drag tires = bad idea

Thing is.... my post was based on more than just an opinion. I've been building and helping build hotrods and racecars since I was about 13 years old. I've personally seen and driven many f-bodies with manual transmissions making over 800-1000 HP at the crank and their 12 bolts lived for many many race seasons with hard launches on slicks. I had my stock 10 bolt in my 1997 TA WS6 for over a year putting 488 to the tire. Granted it was an automatic, but I also left off the transbrake with approx. a 4400 flash speed, so that is just as much of a 'shock' to the rear end as a clutch dump.

I had a TA Specialties aluminum rear girdle with main cap studs installed. I truly believe in these, and I feel that these alone significantly increase the deflection that is associated with the early death of these 10 bolts.

To simply say that 500HP through a T-56 and a 12 bolt = a bad idea, just isn't very smart at all and tells me that you probably really haven't been around racing very much. Not saying you are, but lots of people are just regurgitating comments that they heard on the internet regarding the durability of a properly setup 12 bolt.

An basic "out-of-the-box" Moser or Strange 12 bolt will easily handle 800 crank HP. Upgrade to a 33, 35, or even 40 spline Pro Race type axle, lightweight steel spool, heavy duty yoke, 9310 steel gears, and main cap studs with a support cover, and 1000 crank HP is easy. Go to a 3.250" bore case, and you can put even more power to it......And there are many more upgrades available.

A 9" Ford type rear end eats up about 3-4% more power due to the fact that the pinion center-line angle is more than that of the traditional 12 bolt. A 9" pinion center-line is 2.250" below the ring gear center-line. A 12 bolt's pinion center-line is only 1.5" below that of it's ring gear centerline. When comparing a similarly setup 9" and 12 bolt, the 12 bolt can be about 10-15 lbs lighter than the 9".

For most street/strip cars under 1000 HP, standard trans or not, slicks or not, the choice is obvious.....12 bolt.