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Opeler
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Discussion Starter · #1 ·
I think this has been done before- just wondering if anyone out there had some better solutions...

I'm trying to use the Isuzu Impulse rear end for my V6 GT project. with that, I'll get
4" wider rear track
Limited slip dif
vented rear disks
and a rearend capable of handling a lot more power than I'm likely to get out of a naturally aspirated 3.4

the Isuzu rear seems like a logical choice since the track is nearly right, and you can just about bolt up the stock trailing arms to the GT pickup points. The panhard rod does go the oppisite way

Here's my issue:
Isuzu used a 4-link rear, and as we know, the Opel had a torque tube. I would like to break as few SCCA SM2 rules as possible, as this car might one day make it out to do some parking lot warfare. As such, I need to use the stock suspension pick-ups on the body. It would be pretty tricky getting the 4-link arms to attach to where the torque tube attaches to the body. The most logical approach at this point, so it seems to me, is to just cut the 4-link pickups off the isuzu rear and fab or cobble together a torque tube. I started taking apart the rear end from my parts car, looking for ideas or maybe something that I could used to adapt the Isuzu to a torque tube.

Just when I'm starting to feel real smart, I realize that the Isuzu rear end isn't really symetrical. DOH!!!! It's about 2 inches off center due to the way the housing's made (see pic)

Can I have a torque tube going off at some funny angle - which of course, it would seem I would pretty much have to fab it all myself. Which typically translates into it's going to be HEAVY.

Got any slicker solutions?

Sorry- pic is really dark, guess I sould've used the flash, huh?
 

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Old Opeler
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5,564 Posts
Turbo Diff

What you have is an Isuzu "Turbo" diff with the four link connections.

Most other use of an Isuzu diff is the NON-Tubo one which has similar hook-ups to the standard Opel diff. Infact it is a "B" series Opel diff - like in the latter Mantas. It is no stronger than the standard diff as it has the same parts in it. The Opel torque tube bolts on to it - but not so with your diff.

Your diff is the one Isuzu used to replace the Opel diff when they began having diff probelms with 180 (ps) horsepower.

"Just putting a torque tube on" will be no simple matter and would be less usable that a four link setup. Search for "Toyota Diff" on the board as that may give you some info on a similar instalation to yours. I think both Bobs have done something with Toyota diffs.
 

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Senior Contributor
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903 Posts
When doing my Toyota axle conversion(which I consider to be a better option than the Isuzu BTW, but to each his own) I had planned to build a torque arm. Once I placed the axle under the car with the new driveshaft and pushed the axle up to full bump, I quickly realized that there was VERY little room in the driveshaft tunnnel to add an arm. This was when I decided to go to a three link. I'd highly suggest that you place the axle under your car and check for clearance at full bump. It may be that the offset pinion leaves you some extra room and all will be well or it may hit the side of the driveshaft tunnel, which could be a real problem within the SM2 rules. Good luck

-Travis
 

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Opeler
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89 Posts
Discussion Starter · #4 ·
let's assume I'm going to keep this rear for the time being (its to cold to go back to the junkyard!) and make it work...

From what I'm hearing and reading, it looks like there's going to be a lot of fabrication in the near future.

I guess the real question now becomes fabricate torque tubes or somehow make the 4-link or 5 link, rather, isuzu suspension creatively attach to the GT mounting points for the torque tube.

or just cheat. (autocrossers look away) and fab suitable mounting points for the isuzu rear on the Opel body.

what to do what to do... has anyone done something like this they'd like to share pics of?
 

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Opeler
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Discussion Starter · #5 ·
Just had another thought -
If I run out of room in the drive shaft tunnel (as I likely will, it looks like) would there be anything illegal, unethical, or otherwise unadvisable about just making the drive shaft tunnel bigger? My thinking is that this would fall under the 'modifications needed for authorized modifications' clause in the SM2 rules, and it certanly wouldn't save weight - it would actually add some weight for more sheet metal for the tunnel and the weight of my sloppy welding.

It wouldn't look to bad since the tunnel is hidden under the back seat like shelf thingy on the inside.
 

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Senior Contributor
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Just a thought. With a V6 setup and a "Closed" type diff, why worry about a t-tube? Use a shortened std. drive shaft. Just set your trailing arms where you need them for stability and weld the mounts in. My 2c's.
 

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Opeler
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Discussion Starter · #8 ·
Thanks for the link Travis-

BTW- Hippie - I would do that, and I'm calling it 'option 3', but in the event I take it autocrossing, welding non-stock suspension pick-up points to the body is a class no-no. I may try using a loophole like making a big subframe structure that I can bolt to the torque tube screw anchors, as this would atleast fall in the grey area of the SM2 rules.
 

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I've heard rumors that the SEB made a clarification of the rules saying that subframes were not allowed, though I've not seen it in print myself. I believe they required that the point of rotation at the body remain in the same place...

-Travis
 

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Premium Member
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sprint car clues

Here's a "what if" for you:
How about making just one side into a ladder bar. It should act like the front axle on a sprint car, where the one side keeps it from rotating, but both sides don't get bound up like they do in a full ladder bar set-up. It sure wouldn't take a lot to try it out.

Otherwise, with that particular axle's lower arm set-up, I'd say mount your sway bar to the rear of the axle with the arms going forward along the bottom of the arms, then reinforce and use the sway bar mounts for short upper links. They ARE already there, and all...
 

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boomerang opeler
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5,636 Posts
if you have to use the orig mounting points can you use a "WATTS" linkage instead of the panhard rod?
 

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Opeler
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Off the rear end subject put related.

I sent an email to the SCCA for clarification of the SM rules as I was investigating putting a Buick 215-V8 in a Manta. The response I got back was that this would not be a legal swap under the current rules. Unless you are swapping in an Opel V-6, you may have problems classifying your car in SM.
 

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Opeler
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Discussion Starter · #14 ·
oldopelguy said:
Here's a "what if" for you:
How about making just one side into a ladder bar. It should act like the front axle on a sprint car, where the one side keeps it from rotating, but both sides don't get bound up like they do in a full ladder bar set-up. It sure wouldn't take a lot to try it out.

Otherwise, with that particular axle's lower arm set-up, I'd say mount your sway bar to the rear of the axle with the arms going forward along the bottom of the arms, then reinforce and use the sway bar mounts for short upper links. They ARE already there, and all...
I'm listening - but not too familiar with sprint cars - where do you think I could get a good look at the ladder bar idea? I suppose using the sway bar links would be pretty legalish...

garrymc said:
You might know this...some Impulse have a very Opel looking torque tube. That one maybe easier to swap ?

Garry
Yes, I have discovered that now, but I'm trying to make this rearend work anyway - one because I don't want to go back to the junkyard, and 2 because from what I understand, the torque tube isuzu rear ends are really no better than the stock Opel.

kbishop said:
Off the rear end subject put related.

I sent an email to the SCCA for clarification of the SM rules as I was investigating putting a Buick 215-V8 in a Manta. The response I got back was that this would not be a legal swap under the current rules. Unless you are swapping in an Opel V-6, you may have problems classifying your car in SM.
Yes, I know, and I expect this will be an issue to contend with until it actually gets protested. I sent my own email to the solo rules board and they determined that since the 60-degree V6 and it's derivatives are so commonly used in current opel vehicles (Omega, Speedster, etc) that it would be a legit swap. A lot of the reasoning, I'm sure is based on how little metal is removed from the comartment to facilitate the conversion. Of course, an email is better than nothing, but it really isn't an official ruling until it is protested. I know no one in our local club would protest the swap. I seriously doubt this car will really be competitive at the national level, and as such, not too many people care to protest 15th or so place! And if they do, bring 'em on! If nothing else, I'll get my name published in Sportscar over it! (Which is a more likely way of getting MY name in there than placing at nationals with my driving!) If I really want to be class competitive autocrossing, I'll take my Subaru. The Opel would be a lot more fun though.

BTW- thanks to all for the suggestions... there's an answer that will work in here somewhere...
 

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Member
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Yes, I have discovered that now, but I'm trying to make this rearend work anyway - one because I don't want to go back to the junkyard, and 2 because from what I understand, the torque tube isuzu rear ends are really no better than the stock Opel.
I think you are right about the Impulse rear axel, its probably not stronger than than the Opel.

You do get a slightly lower gear and disk breaks from it though.

Garry
 

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Old Opeler
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Ersatz Torque Tube

You may be able to use the fact that the diff is offset to one side to your advantage as it will leave a bit more room one side than the other in the driveshaft tunnel.

If you fabricate "half a torque tube" that bolts on to the studs that hold the centre " pumpkin" (diff head) in to the housing you may be able to use a steel brace torque bar that is only a part of a torque tube on just one side of the driveshaft.

The drive shaft would have to have a centre bearing where the original Opel diff had its forward torque tube pivot point and the fabricated brace would have to mount on this line across the car too and require a pivot ( big rose joint???) here too.

Maybe a wee scetch will help:
 

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Old Opeler
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Bend in the Middle

The drive shaft will have to be able to bend in the middle with a universal joint behind the centre bearing - just like old Studebakers from 1950 t0 1955. There would have to be a mount for the centre bearing and the pivot for the torque bar end fabricated to fit up where the Opel torque tube used to pivot.

Hope that helps.
 
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