Suspension Question
 

My Cobra has the independent Corvette C3 mono leaf setup. I don't mind it except when I hit a bump, it seems to bounce back a little too much, actually feels like the tires come off the ground. I'm sure this is in part due to the lightness of the car. I have spoke to some Corvette shops, no softer leaf is available. I'm sure the suspension compresses ok, I think it just rebounds a little to much and too quick. I replaced the shocks with some inexpensive sensa trac's, maybe that's part of the issue as well.

So, my question is this, can anyone recommend a good quality shock for this issue or am I targeting the wrong component. I'd love to swap in a full coilover setup but haven't bugeted for it yet.

I will be autocrossing it this weekend, hoping for a relatively simple solution.

Mike

i don't think you'll be to fix it completely until you replace the leaf spring with coilovers, it is releasing stored energy.

I don't have any problems with my Corvette IRS. I'm also running the stiffest rear spring Vette Brakes makes and the Monroe's you mentioned. Tires off the ground, ain't never gonna happen, unless you're flying over a hill. Granted coil overs would be the ideal set up, but I've found, for me, they're not needed.

Mike!

I thought I was the only one with a C3 unit. Sure would like to talk, there are options for springs. I do not have any problems either.

My EM Cobra has C4 suspension including fiberglass monosprings front and back. I've never experienced what you describe, but I did improve my handling by going to adjustable shocks all around. I went with QA1 brand shocks. .... My 63 Corvette coupe has modified suspension with fiberglass monosprings front and rear. They can be adjusted by moving a pivot point along the spring to make the moving portion of the spring either longer or shorter. Look to see if you have such an option. .... Many C2 Corvette guys who switched from stock steel springs to fiberglass springs complain about the stiffness and bumpiness of the ride. Sometimes the problem is that the driver is expecting these old cars to ride like a modern Lexus. Other times a change in shocks can help.

Your description of your problem of too much bounce after a bump leaves me wondering exactly what is happening. If your shocks are not providing much dampening, the spring should deflect a lot at impact with the bump, making for a soft impact. But that same soft dampening would allow a lot of follow up motion as the spring flexed back and forth a few times. On the other hand, if the shock are providing a lot of dampening resistance, the spring will deflect very little and the entire car will rise over the bump making it feel very abrupt to the driver. In that case there should be very little rebound after you pass over the bump. So which sounds more like your situation?

One more thought. Tires also act like springs in the suspension. Taller sidewall tires like Goodyear billboards on 15" rims have more spring like action (deflection) than shorter tires like low profiles on 17" and 18" rims. Higher tire pressures act like stiffer springs and lower pressures act like softer springs. Adjusting your tire pressures for your driving situation might help too.

I've got the C-4 suspension, but use C-3 springs because you can get a higher spring rate. BTW Vette Brakes made the spring for EM. I've got a brand new one, that is Cobra specific, if anyone is interested. Used for a couple of days, then changed out, not stiff enough for me.

One question I have is how long are your forward trailing arms? Factory length is 14" and my guess is that would have to have been shortened. This may have add problems.

VanSteel can make up a composite spring for you. They actually would have Hyperco make it. But you need to go through a dealer and VanSteel is. VanSteel also make a coil over kit, but then you get into how long are your trailing arms? They would need to be modified and they are damn expensive.

Then there is Dick Guldstrand, that has a nice conversion, that is the way to go in my opinion. However a conversion of that would still be needed.

Added: When I say 14", I mean from the centerline of your half shaft to the mounting point. If this is shorter you would lose shock motion per wheel travel.

Thanks for all of the helpful responses. I have however determined that the rear suspension is a C4 not a C3. I still suspect some worn bushings but I'm still not sure how to keep the car from at least feeling like it's going to leave the ground.

Hotfingrs, I looked up Vette Brake, turns out there local to me. They have some good replacement components that I may consider purchasing.

Tommy, When I hit big bumps the car does feel as though the leaf doesn't compress, however, when I look at video of my car leaving the line hard at the drag strip, it compresses quite a bit. That's why I was leaning towards the quick rebound of the shock giving me the bouncing feeling.

I'll know more once I auto cross it this weekend I guess.

Mike

I had to put bump stops on my rear because it squatted so much when I nailed it that the tires rubbed.

Mike,
It may be that the duration of the drag strip launch is so much longer than the duration of hitting a bump, that the shocks don't have time to allow the springs to move when hitting a bump. My guess is that the bounce you are feeling would be less jarring if you had softer shocks. BUT, your car will likely handle better on a smooth autocross course with shocks that feel stiffer. The optimum shock settings for my car and my driving style is fully hard on the front and fully soft in the rear. It helps me deal with oversteer.

Also, everything in the rear is heim jointed, four link, toe rods, strut rods, sway bar

http://www.dragvette.com/

http://www.dragvette.com/Steve_6-Link_copy.jpg

Dan.
I believe that's only for C-3 suspension.

Elegant Motors never got past the C3 so this is for Mike.

Correct me if I am wrong. In Mike's pics I see deep dish wheels. Most guys I am aware of running a C4 rear do not narrow the half shafts. So C4 Cobras do not have deep dish wheel. But if it were narrowed that would mean a narrowed spring making it stiffer. The C3 does need to be narrowed.


http://www.clubcobra.com/forums/albu...pictureid=4151

Thank you for all the responses.

Dan, I'm still not sure if I'm using a C3 or C4 rear end. What should I look for? I have pictures in my album now under "Details" but don't know how to put them in the thread, I tried but not sure if it worked.

Thanks again everyone!

Mike

Mike,
That is not a C3 but a C4. The C4 hub bearing carrier is full floating where as a C3 has a trailing arm.
Your differential cover should be aluminum with the so called Bat Wing. Your's does look narrowed I think. It also looks as if your upper shock mounts are moved in quit a bit. You may want to try and move them outward.

C3
http://www.acp-euskirchen.de/zubehoer/c3_achse1.jpg

C4
http://www.scottiegnz.com/irs-front.jpg

Mike you may want to check with VanSteel for parts also.
They are in Clearwater. They seem to be some nice guys also.

http://www.vansteel.com/

Yours is a C4 - for sure, thanks for the picture, but your halfshafts should be aluminum and yours look like steel (like the C3 halfshafts) from the rusty appearance. I suspect your C4 IRS has been narrowed and the halfshafts replaced with steel ones, which may be good from a durability standpoint.

If it is narrowed, the spring is also shortened and if not made narrower, will have a wheel rate well in excess of the original vette it came from and then is compounded by being in a lighter car...

On mine (not narrowed), the Vette rate was too high for my lighter car, so I shaved the sides of the composite spring to reduce the rate. The rate is directly proportional to the width of the spring, so if you make it 10% narrower, you get 10% less spring rate. I shaved the springs with a band saw first (leaving the center and ends full width so the mounting is not altered) and then sanded smooth with a belt sander. Mine has been this way for over 15 years, so do not worry about if this somehow damages the spring. Do not alter the top or bottom of the spring (do not make it thinner) - only alter the width. This is also a one-way street, so do this process in small bites; there's no going back!

I also see your shocks are at a steeper angle, which will make them effectively softer (less control), but I have found that typical Vette shocks are also too stiff, partially because my wheel spring rates are down from Vette stuff, and partially because my Cobra is lighter. I also use the QA1 adjustables at the front and find that I only use 3 clicks for road racing and zero clicks for drag racing.

Vette Brakes is your best source and they have heard of this before because I have consulted them numerous times.