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Discussion Starter · #1 ·
I'd like to replace my GT's rear suspension with an unequal length a-arm configuration, and presume that the mosy likely source for one of the right width is a sport compact car...

Any suggestions?
 

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Detritus Maximus
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Miata.
 

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Not too many current offerings with RWD out there. Mazda RX7, Honda S2000, etc....most are expensive. Plan on some major rework of the floorpan, and a custom driveshaft too. You'll have to narrow the a-arms and halfshafts too, either that or widen the GT body, as it's quite narrow compared to the contemporary modern car.

Bob
 

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Discussion Starter · #4 ·
Yes, yes, yes. A Mazda Miata sounds good, but is probably too wide; I'll check into it...
 

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IRS

I am no Mazda expert (as I am about to demonstrate), but would an RX-7 rear setup work? I see in my old (1978!) R&T magazine that the first Gen RX-7 was a live rear axle, but the second Gen (1986-91) had an IRS setup. The 3rd Gen also had an IRS, but who can afford THAT?

For some details on the 2nd Gen RX-7, look at
http://www.rx-7.org/2ndgen/specs2.htm
(Ah, the power of a Google search!). With a 56.7 inch rear track width, it's pretty wide compared to the GT at 50.6 inches. Maybe the half-shafts could be shortened up? I suspect that half-shaft mods would be the LEAST of the work for any IRS install. I can't imagine how much work it would take to modify a GT to accomodate the links and mounting points that would be required for an IRS graft.

If we're doing the "flashback" thing, what about an E-type Jag IRS? As I recall, that was all the rage back in the '70's when George Barris et al were building custom dream cars. Which a GT with IRS probably is. JMHO
 

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I think you've hit the nail right on the head Keith. Unless it's for strictly show, it's a lot of work for a moderate increase. Most of the improvement in handling from the IRS is gonna be in ride quality....important, sure, but any factory-engineered geometry for let's say, a Miata...is not necessarily correct for a GT. And mounting all those pickup points, and making them strong enough without adding tons of weight is the job of an engineer.
The car will have greater body roll, so larger sway bars are ncessary too. It would look cool though.

Bob
 

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It does sound like a big job, but if you're gonna take it on another posible (and cheaper) source would be a rear from a80/early 90's thunderbird. Some of them came with IRS. I'm sure if you looked around you could score one real cheap... It is gonna be wider than any of the other ideas, and may not even have a chance of working in there, but might be worth looking into...
 

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Opeler
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re-independent rear suspension

Here is a possible rear end transplant you may want to look into. From 1968 on Triumph gt6's had an independant rear setup with a transverse leaf spring arrangement(cant get away from them things! hehe) Spitfires also got this arrangement installed from 1970 on. Hearalds and Stags also had the newly designed rear end around this time.
The track width of this setup is 49" And it doesnt appear that a lot of floor changes would have to be made to occomidate this change. it looks possible that the triumph frame(it has a full frame) could be used as a rear sub frame in an opel.
I have not tryed this change or heard of anyone who has,
but it looks like something that could work. try this link http://www.gt6man.freeserve.co.uk/Adverts/GT6-mark2-profile.html this link gives a decent view of the rear assembly.
Good luck.
 

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Detritus Maximus
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Re: IRS

kwilford said:
I am no Mazda expert (as I am about to demonstrate), but would an RX-7 rear setup work? I see in my old (1978!) R&T magazine that the first Gen RX-7 was a live rear axle, but the second Gen (1986-91) had an IRS setup. The 3rd Gen also had an IRS, but who can afford THAT?

For some details on the 2nd Gen RX-7, look at
http://www.rx-7.org/2ndgen/specs2.htm
(Ah, the power of a Google search!). With a 56.7 inch rear track width, it's pretty wide compared to the GT at 50.6 inches. Maybe the half-shafts could be shortened up? I suspect that half-shaft mods would be the LEAST of the work for any IRS install. I can't imagine how much work it would take to modify a GT to accomodate the links and mounting points that would be required for an IRS graft.

If we're doing the "flashback" thing, what about an E-type Jag IRS? As I recall, that was all the rage back in the '70's when George Barris et al were building custom dream cars. Which a GT with IRS probably is. JMHO
Having a 2nd gen RX7 and having taken apart a parts car, I think it might be too wide. If you could fit it in the car, it would probably require the wide fender flares and wheels with a high offset. I do know that 2nd gen rears have been put into Miata's (along with the Turbo 2 motor!).
One way to do it might be to build a tube frame rear section with all the suspension/diff mounts already in the right places (much easier to do on the floor or bench rather than 'in the car') and install it into the GT. It would probably mean cutting out most of the GT's rear floor and frame and fabricating new stuff instead of trying to mate the two together. Kind of like how the Pro-street people 'back-half' a car.
Or I'm dreaming.
 

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My race Spifire had IRS. Never drove another car that would go through a salom better. Don't even think about it, however. Is was way too weak. I used to break rear axles on a regular basis. I thought about beefing the axles up, but figured then I would break something more expensive to replace. I think the GT6 rear end was beefier, but I have no first hand knowledge.

I have seen a 2nd gen RX7 parted out and think that the complete rear would be too heavy to use in the Opel, unless you used just the diff and custom built eveything else.

My 3 cents
James
 

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Keep it German?

I have parted out a couple of 3 series BMW's with IRS and they are a nice unit, with the same bolt pattern for the wheels, too.

Datsun 510, 610, and Z cars us a very easy to resize IRS unit, (uses u-joints instead of CV joints) but it typically has issues with camber. Their differential is probably your best bet for a custom fabricated rear suspension....

I do think it is probably too much work for the result, though, and would recommend trying some more conventional approaches first. See what you think after new springs, bushings, sway bars, adjustable track bar mounts, and quality shocks before you sink the big $ into reinventing the rear half of the car.

Just my $.02 worth.
 

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Opeler
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Re: Miata suspension

The width on the Miata is considerably wider than on a GT. I put my GT and my brothers Miata back to back and you can see a difference in the two. the Miata even uses a deeper offset wheel ( around 40 mm ) making the flange to flange width even more drastic between the two. It'd work well with flares on the GT with the right rims. It might be a better fit into a Manta, even so it might require different rims there too. There is a swap of a Ford 5.0 L engine into a Miata where they put in a diff, from a T-Bird I believe, in the stock suspension.

Instead of trying to build a existing complete setup into the Opel, why not create a complete subframe from scratch and use the hard to make parts: knuckles, spindles and arms(maybe) from a existing setup and do it that way? Might just come out lighter and stronger.

I've been tossing around the idea of a AWD GT for the longest time. I just need the money to do it. Taking donations....

ALan
 

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Discussion Starter · #13 ·
For simplicity in interfacing to the existing unibody, and superior traction with a bit less body roll; my only alternative (since *I am* going to drive my GT again) to a dressed up GT stock rear is an unequal length a-arm suspension mated to a box-steel subframe.
I'd rather save time than money and so continue to search for a pre-fabricated rear - in which options are severely limited to this narrow track of ~50in. since I want to retain the stock body.
Any references?
 

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That's not struts....that's a Kadett C (1974-1978) front suspension. Relative to our lowly Chevette here. It's a fairly common swap in Germany.

Bob
 
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