I decided the rear suspension rebuild on my 80 model wasn't going to be expensive enough so I'm going to swap in a C4 rear suspension while retaining the stock center section. Has anyone ever performed this swap?

 

Wast expensive neough eh haha? Well yea it has been done but you are going to have to do some major major frame work, Try this link and this one is for the front, but I think its still applicable here is another one for the 6 link, which is probably easier to do than the 5 link per side C4 setup 6link


Good luck


Here is a link to Guldstrand Motorsports, these boys make some rather fun stuff for the high performance vette... they have a 5 link thats weldable in place, and to be honest, Im interested in it myself. Im trying to determine whether or not it would offer substantially better handling and performance than just a full on rrebuild in the rear with transverse composite springs and smart struts etc.

Guldstrand

 

TT will have a good answer. He was going to adapt a c4 rear to his car but ended up going the custom 5 bar route.

 

Are you going to use the C4 halfshafts and control rods? If so, you have a problem. The track width is much wider and that means flares or neg. offset wheels (yuck). Then theres the problem with the frame, the hubs are huge on a c4 w/ all those attachment points on there, it would require notching the frame. Then there's the spring, it would have to line up, the C4 diff has the stub axles located in a different position (fore/aft) so the spring alignment would most likely be out of whack. You could install coil overs (not easy). Then there's the trailing rods, they will not be in the right place, you would have to build custom ones or weld a big bracket on the frame. This is the reason I built a custom suspension, a lot more work but IMO more elegant, the toe control stuff is in the right position, unlike the C4 one that's on the lid. That is not an ideal place, in fc for most of the suspension travel it's the wrong place, except for close to horizontal halfshafts, the angles will change leading to toe changes (not as dramatic as C3 but still there) and the early C4s w/ the control rod positions have a high roll center, leading to jacking.
Here's some pics that will show what I mean (this is a D36 C4 diff)

Last but not lest (and important IMO) there's the issue of the parking brake, either use the early drum brake or the later one that has the PB as part of the caliper, either way you're stuck with those junk C4 calipers or you'd have to update those also. The studs on the C4 hubs are also thicker than on the C3 (7/16)

 

i'm planning to go with it when i do mine

 

Hah by any chance do you know more about it than I do? hahaha Im fairly set on doing it, its just a matter of what I need other piece wise and if Im going to have to further modify anything to make a coilover setup work in the rear there.

 

Why would you not just use C4 wheels?

 

?? who?? what?? hahahaha??? Fairly set on doing what? 5 bar or C4 suspension? They are not the same thing, similar but not the same. I'm just sharing my findings here, take it for what you want. (I have a good memory and have not forgotten the things said in the past, I haven't forgotten about you kid)

 

neg. offset wheels on c3 ...

 

We used an entire 1985 C4 suspension in my 1977. The front went in stock, and the rear needed an inch and five eights reduced on each side to get the wheels into the wells. We plan on using C4 17" wheels which will bolt right on with no fitment issues.

If you use an 88-96 Corvette suspension, you will have to reduce both the rear and the front width to get the tires into the wheel wells. Very doable, but the fabrication is time consuming and expensive.

Spike

 

TwinTurbo, is that a picture of your frame with the C4 suspension mocked up? Is that setup narrowed? Did you decide the frame would have to be notched for hub clearance if the supension was narrowed?

SpikeZZ4, You said the rear needed to be narrowed to put the wheels where they should be, do you mean C3 wheels? Which year C4 wheels were you planning to use, early or late? When you used the 85 suspension did you also use the differential housing? Do you have any pictures?

 

Unforgiven,

It's a stock C4 IRS, late design w/ the parking brake in the caliper. Not Narrowed. The frame would have had to be notched if it were narrowed (C3 halfshafts used), if you use it in stock form you have to go with neg. offset c4 type wheels or really big flares. Since I have 12" wide rear wheels that would have meant really big flares so I never used that system, it is a mockup and I abandoned it. Too much work, crappy brakes and not even an ideal toe control system, short trailing rods..I felt I could do it better without all the C4 IRS compromises and chopping up the frame so I built this:

 

OMG,

Nice shots twin_turbo, that is an insane rear suspension setup, I love shots like that.

Just out of interest what are you guys doing with your vette's? I am very impressed that C3's had IRS as standard, unless you are doing some serious track work and need to be able to dial your suspension settings to perfection I would consider spending money elsewhere first.

IMHO If you are doing it purely for boasting rights wouldn't you be better off swapping in a TPI motor that can be seen much more easily than a very complex rear suspension swap.

Cosmicvette

 

A tpi?? That's not boasting. this is





but seriously, it's not for boasting, the C3 IRS has terrible torque steer and toe control problems, I like(d) to drive my car hard and what I'm doing is trying to get it handling the best I can and it's fully adjustable. If it fails it'll still look cool

 

TT
You do some awfully nice work!

 

OMG again!

Ok that puts the look of a tpi to shame, hmmmmm quad webered twin turbo setup you certainly live upto your nick. I think I have located the cause of your torque steer problems it wasn't the rear end at all it was under the bonnet

Have you used weber's (or delorto's for that matter) in a blow thru setup before? I tried this on a 6cyl car I had with triple webers and a blow thru single turbo setup and had nothing but problems, I ended up installing weber style throttle bodies in place of the webers and going efi after fiddling with it unsuccessfully for the best part of a year. Although I was trying to use the car as a regular driver which probably wasn't the best idea in the first place

I would love to see any more shots you have of your car, you do some pretty impressive work!

Cosmicvette

 

They are 45 DHLA dellortos off a lotus esprit turbo, so called tri jets. They are pressure tight and have the 3rd jet for boost (and high rpm) so they work perfectly w/ a turbo system. I may swap to TWD or luminition TBs if i get tired of the carbs.

More shots at http://members.home.nl/m.b.p.jongman/?C=M;O=D

 

Unforgiven1,
We will use regular C4 17x91/2" wheels with P285/40R17's all around (we do not know which ones yet). With this set-up, the rear has to be narrowed 3" to keep the wheels in the wells. I suppose you could flair it and it would certainly work much easier. We used the Dana 44 from the 85 Corvette, which requires modifications to the rear under body with the storage compartments. Lots of fabrication to make it work correctly.

Unfortunately, all my pictures of that area are film. Eventually as we begin construction again after Power Tour I will be able to take them with digital. Then I will have to figure out how to post them.

Spike

 

Why do you have to modify the storage compartments for the D44 ? It isn't significantly wider than the C3 one and the batwing is narrower.

 

Okay, I'm a little confused. (Which is good because I'm learning)

Twin Turbo, by your measurements did you decide that C4 wheels would fit without narrowing the rear? If so did you use measurements from 84-87 or 88 and up wheels? 84-87 have less neg offset, correct? Did you use a C4 diff or a C3 in your mock up? Your new suspension looks killer. I really like the detailing of the halfshafts. Which ones did you use? Unfortunately, I'm trying to get this car back together for the Power Tour so I'm trying to minimize the amount of fab work involved and still end up with something better than stock for my investment.

SpikeZZ4, You used 84-87 or 88 and up wheels?(I think that break is right) You narrowed the rear 3"? My plan has been to use the 80 model Dana 44 and batwing with the C4 suspension and halfshafts.

I'm kind of attached to the stock suspension after all the work to clean and rebuild it. It just makes me cringe thinking about the halfshafts supporting the rear. Especially with a six speed ahead of it.