Opel GT Forum banner
1 - 18 of 18 Posts

·
Opeler
Joined
·
9 Posts
Discussion Starter · #1 ·
Hi Guys what rear end has been used with the v6 motor swaps? I saw an Isuzu rear end in the junk yard that looks very similar to the GT rear end ,has anyone used one and could it handle the power? I want to keep the original bolt pattern but want something that will last. Thanks
 

·
Super Moderator
Joined
·
14,180 Posts
The non-turbo Isuzu rear end (which people use for the disc brakes) has the same size ring and pinion/differential as the Opel. Therefore it is really not any stronger than the Opel differential (not sure about the side gear/pinion gear hardness compared to an Opel, but this is the weak link in the Opel diff. due to the brittle nature of these gears...they explode under duress).

The alternative is to install a limited slip diff. in either the Opel OR the Isuzu rear axle, but they are expensive and hard to come by, and you still have the relatively weak torque tube design to contend with. I'd try to find a relatively small and common rear axle that you can get parts for. Sure, a 9" Ford could be used, but those are heavy in comparison and physically much larger to try to fit to an Opel. But a Toyota 7.5" or 8" truck rear axle, or a Ford 8" rear axle, or a smaller GM 10-bolt would work (I prefer the front-loader rear axles, easier to work on).

Bob
 

·
Opeler
Joined
·
9 Posts
Discussion Starter · #3 ·
Thanks Bob for the advice let me ask you a question,does the Isuzu rear end fit ? I'm asking because if it fit I could get the whole deal and get a sway bar and the springs from the much heavier Impulse. I saw a post from you talking about Opel using the Ascona inner workings in a GT houseing to take the power from the Rally cars are these parts findable for a reasonable price? Thanks Ric
 

·
Super Moderator
Joined
·
14,180 Posts
The Isuzu housing is about 4" wider than the GT housing. You'd need substantial flares to fit it to the car, or you'd have to use front-wheel drive offset wheels.

As far as cross-referencing parts from other Opels.....no, they're not easily obtainable nor cheap. A limited slip (ZF) would set you back about $1200 or so, a GM bearing and shim set another $400, plus the labor to install it. And then if you decide to change gear ratios, another $300-$900 depending on the ratio. And then you STILL have the weak torque tube, which requires at LEAST an overhaul of all the parts if it's gonna take the abuse of an engine with more torque. New 'donut', new side mounts, new top/bottom bumpers, possible new T/T bearing. More $$$.

A swap is more labor intensive, but far cheaper in the end. Travis went this route for his, GT, narrowing a Toyota truck rear axle, but he also was able to pick up a limited slip and 4.88 gears for a LOT less money than anything Opel.....and it's a ton stronger. I mean, they put Small Block Chevys into Toyota 4 X 4's, and even with the added weight of a truck plus V8 (3300 lbs +), they hold up to most normal use.

Bob
 

·
Super Moderator
Joined
·
14,180 Posts
What is the availability of limited slips, OEM or otherwise? Nice to have a stronger rear axle, but if you're putting out enough power to break stock Opel rear ends, you need a limited slip to put the power down to the ground for sure.

Bob
 

·
Member
Joined
·
315 Posts
In all of this you may have overlooked the Quaife ATB differential to fit in the standard rear-end housing. Although it's initial cost is a little high... about $1100 retail... it is guaranteed forever for any application including racing. We are using one of these in our Nissan E-Production race car which puts out about 240 HP and have had no problem. (We also have been using one in our F-Production Opel for about 5 years. ). Although the housing for the Opel is a little different than the Nissan (but not by a lot) the "guts" are the same.

This does not solve the problem of an old torque tube, but almost anyone with reasonable mechanical skills and common tools can rebuild it like with the new parts Rally Bob mentioned above. If any one is interested in doing this, we will do one labor free (you pay for the shipping and parts) so we can post pictures of the process here on the Opel GT board. Contact me by email... [email protected]
 

·
Registered
Joined
·
92 Posts
I'm personally going to go with the Ford 8.8" out of the 86-96 Mustang. It's lighter than a 9", almost as strong when you change to 31 spline axles, very plentiful, easy to fix and easy to fit to the rear end of the Opel.

Here's someone who modded a 8.8" to fit his Opel GT:
 

Attachments

·
Premium Member
Joined
·
1,802 Posts
Camaro

The Camaro 7.5" is just as easy to find and modify, and it has the advantage of already having bosses on the front where a torque arm was attached. Plenty of gear ratios and lockers available from the S10 4WD crowd as well. It would be my first choice for the swap.
 

·
Super Moderator
Joined
·
14,180 Posts
I'm not knocking any of the readily available US-made differentials, but there's something to be said for a front-loader like the Toyota. If you set up an extra 'chuck' assembly, a gear swap can be made in 15 minutes. Try that with a rear-loader!

Bob
 

·
Member
Joined
·
299 Posts
i need to updated my former 2 cents
an isuzu rearend is a front loader rearend like the toyota unit plus you have a good variety of stock gear ratios 3.44 3.73 4.10
some came factory with LSDs some not but these would be the 4x4 ones they are very close to the correct size, they came behind v6s and they are a gm unit :) they have a good aftermarket like the toyota but not as cheap
but heres the thing i find the best
the trooper units all came with rear disc brakes which i think is a plus
this is what my swap is consisting of
the trooper unit with rear discs
single piece drive shaft
and a truck arm style suspension like in winston cup nascar
it eliminates the torque tube/arm approach and is the best setup for both drag racing and road coarse and it also makes a leaf spring axle an easy swap because it uses the leaf spring pads to attach to,which are at the same spot on the opel axle
for more info look at www.hotrodstohell.net they will make a custom setup so it will be easy
i also think it is a much cleaner setup
as soon as i have more funding i will be doing this so i will keep you posted on my own thread
 

·
Senior Contributor
Joined
·
903 Posts
I took a quick look at the truck arm suspension and have a few comments.

Be carefull with anyone that claims any one setup is the best for both drag and road racing. The requirements in rear suspension geometry are different in the two applications.

It would be interesting to know whether or not NASCAR uses this setup or not. The wording on the web page is sufficiently vague. Even if they are using it, one needs to consider that something that works well in such a narrow application, basicly a fixed turn radius and direction at a narrow range of speeds, MAY not work well in applications with a wide variety of conditions such as road racing or even street driving.

You'd also be giving up the adjustability that comes with most other type of suspensions. Typical 3-link and 4-link suspensions have a great deal of tunability to adjust for the desired anti-squat, brake hop, roll/bump(same thing really) steer and so on...

The other thing that would concern me is why haven't I seen this in the numerous suspension books I've read?

-Travis
 

·
Member
Joined
·
299 Posts
they just emailed me back and asked for the wheelbase and track width so they will probably do they math and send me more info and i know that know design is superior but a good all around setup would be nice
also in reply to the ? as to whether or not they use it in nascar look it up on the net they have used it for years i think since 1963
 

·
Member
Joined
·
315 Posts
A few words on "truck arms".

They are NOT the way to go for road racing. NASCAR does use them because they are mandated by the rules. No other competitive purpose built road race car uses them. This includes the Trans-AM and GT class in SCCA which until this year mandated a "solid" rear end (no independent rear suspension). For those who are not familiar with SCCA rules, Trans-Am and GT cars are allowed to be full "tube frame" silhouette cars. Although some "tub" (non tube frame) cars are still running... they are running at the back of the pack at national level competition.

Stick with the 3 or 4 link suspension.
 

·
Member
Joined
·
299 Posts
yes i would agree to the fact that a four-link suspension is superior but it is also more complicated and can cost more
pus you have to chop and hack the car up up to fit the best 4 link geometry in which i dont want to do
 
1 - 18 of 18 Posts
Top