Converting to 3-Link rear suspension

[v6spider]

I am considering converting to a 3-Link rear suspension. For one and probably the main reason - I need room for the dual exhaust coming from my v6. But also, there are other benefits - less binding up in the rear, simpler, better capability to attain optimal anti-squat & roll-steer characteristics.

I am curious, does the third link needs to be in the exact center of the axle? Basically what I am considering is removing the two upper links and replace them with a stronger single upper link while retaining the pan hard rod. The two lower links I have fabricated are already adjustable the upper wil be uilt the same way. I wil also be making an adjustable panhard rod using the same components.

Thanks!
Rob

[Curly]

Sounds like you need the rear end out of an early 124 AC Coupe (1968 model).
They had a torque tube assembly incorporating the diff, a pair of long lower links, Panhard rod and an anti sway bar. I prefer this set up to that of the later Coupes and Spiders. No idea why they changed.

[maytag]

I like the idea of the torque-tube, but in absence of that, no, the third link does not need to be in the exact center. the third-link setup has only one real downside that I've ever experienced, but with the power we're making, you won't see it.

If you've gone to adjustable lower trailing arms, then with a properly placed third-link (or, 4-link) you can now also adjust your pinion angle, which can be usefull. Again, not AS usefull with the low hp we're doing... but still fun to tinker.

Somewhere on this forum, I once saw a photo of a brilliantly clever setup that had been designed to replace the panhard bar. It had a rotating eccentric on the diff itself, and then attached to the body on both sides. a "Watts" linkage.

hmm. this migh be it (though I thought I remembered it being prettier and more elegant in design, and I thought it was on a Spider. But this is a good thread to get ideas from anyway.)
http://www.fiatspider.com/f08/viewtopic ... it=panhard

Maybe it was on the fairlady-roadster forum that I'm also a part of. I'll see if I can;t find it.

[MNspiderman]

I was wondering if the pumpkin was Iron or Steel. Must be steel if your considering welding to it. Summit Racing has a lot of goodies for what your after.

[v6spider]

I should probably mention that the rear-end I am using is a limited slip unit from an 84 Rx-7 GSL. I was using this set-up in my previous V6 spider conversion car. It currently is setup as a bolt-in for a stock spider using all the same mounting points as the stock rear-end. The lower links have been updated to adjustable ones using 5/8" Teflon lined Chromoly Hiem joints and schedule 80 pipe. The uppers are still the stock spider links with the rubber joints.

Maytag: I didn't think the upper third link needed to be exactly center either, but it doesn't hurt to get a second or third opinion for sure. Interesting you mention a Watt's linkage. The Rx-7 the donor rear-end came from uses a Watt's style of linkage that I originally considered adapting to the spider, but I read some posts on several other forums talking about that particular linkage on the Rx-7 and that it has a tendency to lock up. Also, if I used that linkage it would get in the way of my dual exhaust.
BTW, my spider is not the average low power spider you speak of. The engine that is in my spider is a full roller Chevy 4.3L V6 with over 300 hp. One of the reasons I had to swap out the stock lower links for the custom ones I made was because the lower rubber joints were getting chewed up by all of the torque.

MNSpiderman: I considered a torque tube design. but again having the room for it is a concern of mine one of the reasons I chose a 3-link. Summit and Jeg's - two of my favorite online speed shops! Luckily for me I can go downtown to my local speed shop and by the parts I need without having to order them. and their pricing is pretty close and better on some parts.

Cheers!
Rob

[maytag]

The Rx-7 the donor rear-end came from uses a Watt's style of linkage that I originally considered adapting to the spider, but I read some posts on several other forums talking about that particular linkage on the Rx-7 and that it has a tendency to lock up.
BTW, my spider is not the average low power spider you speak of. The engine that is in my spider is a full roller Chevy 4.3L V6 with over 300 hp. One of the reasons I had to swap out the stock lower links for the custom ones I made was because the lower rubber joints were getting chewed up by all of the torque.

V6Spider:
so, the thing I'd caution about in your application of a 3-link (as opposed to the 4-link) is "crawl" on one-side or other. That is the term we used to use to describe the axle housing trying to twist on one-side under torque. straight line is okay, but under load in a corner (when one wheel is turning faster than the other, and therefore putting-down more torque than the other) the outside end of the axle-housing would try to rotate, and because the 3rd link was creating a pivot point (or fulcrum) the inside end would crawl the other direction.
it's hard on parts, and can create some difficulties in chasing setup issues.
HOWEVER: I'm talking about 500HP+, and more relevantly; over 3500 pounds in vehicle weight. !!! this may not be an issue for you.

[spiderrey]

Alfa romeos use that setup, watts type linkage. I always thought it was kind of heavy.

[v6spider]

Maytag: I didn't consider the possibility of the twisting you speak of, but I certainly see how it could occur in a high HP situation, especially if you are getting great hook-up. In my case, I don't think that will be an issue. For one I am below the 500 hp threshold for sure and the car is pretty light-weight 2600 max. Plus the tires are p225/50/r15's and the rear-end gear ratio is 3.90 so there isn't going to be a lot of solid hook-up at my tire size. The first V6 Spider was a tire shredder for sure. The new version is using the engine out of the old version, so it'll be about the same.

Spiderrey: If designed correctly i think the Watt's linkage is a better setup than the panhard bar that is used on the spider. The watt's linkage eliminates the side to side motion that occurs in a panhard bar setup when the body travels up and down. I agree that it is heavier but not by much. There is a 124 spider out there where someone installed a custom rear suspension that uses a Watt's linkage. And from what I could see they did a great job. I think if your search the forum it is on here.

So I am considering attaching to the location where the Watt's linkage pivot was on the rear-end and then from there to a re-enforced point on the frame-work behind the seat. I am curious as to what the optimal length will be. The original upper links are pretty short. So it would be hard to duplicate the length. It is just that the mounting point needs to be twice as strong as the original.

Cheers!

Rob