Just spoke to Koni and they said they have no available part number for the C4 (1994) in a coil over shock..What part number are you guys using in either Koni, HAL QA1, or AFCO or any for that matter? The 8241-1097 (front) is a standard shock. As always, help is greatly appreciated.
Cheers,
Robert

 

Bob:

I think the problem is that most racing shocks are longer that the production shocks for the C-4, so no one makes a racing threaded body coilover shock.

You can groove your stock shock or a revalved stock Bilstein and add a coilover kit.

The peices are cheap. The Afco coilover kit was 50.00 ea. The 2 1/2 inch x 10 inch coil springs are 50.00 ea. The local machine shop charge me 7.50 ea to mount the shocks in a lathe and groove them .030 deep for the wire snap ring. The only thing I would do different is to put the groove lower, perhaps as low as 1/4 inch from the shock bottom instead of the 1/2 inches that I used (as it was tough to get the spring to fit ... almost too long.) Figuring out the spring rate is the real mojo, but it looks like others have done well with 250-275# rear and 475-500# front. You can put a zip tie around your shock rod to monitor for full travel, you want it shy of bottoming the rod and you don't want to hit the bump stops in the rear (bump stops= evil power on oversteer).

Look at vetteracers post for pics.

 

I am now waiting for exotic muscle to come out with a shorter shock body because I ill be lowering the car 3+". Last time I got the rippie coil over kit I was sitting on the bump stop because it was so low. I believe that the standard bilstiens/fx3 shocks are the same lenght as the standard coil over shock. Speedjohnson, How does putting a zip tie around the shock rod do anything for travel? Would this work in extreme cases of lowering and getting some suspension travel back? What kind of experience do you have with this? I am wanting coilovers now and talked to rippie, they told me no matter what the shock lenght the car will still hit the bump stops, I really didn't believe it when they told me that. Please let me know what you think. :cheers:

 

The zip ties only allow you to monitor the shock travel. You use this to make sure that your spring rate is right. Ultimately, you want your spring rate soft enough to get as much suspension travel as possible, but stiff enough to prevent the car from bottoming out the shock rod (which will ruin the shock). The zip tie just allows you to see how much the shock compresses in full bump (as it will be pushed up on the rod during severe suspension deflection and will stay there for you to look at later.)

DRM is right. The bump stop will bottom you out if you lower the car very much. I merely cut mine off; but I also moved my shock perch up (cut it up and into the frame tube) to allow for adequate suspension travel in bump (since I had lowered my ride height). Then you have to adust for the toe rod angle by moving it up at the rod end or you will get significant bump steer in a severely lowered car.

I suspect that there are alot of lowered street vettes out there that hit the gas, squat the suspension, it bottoms on the bump stops (= rear suspension rock hard), the rear tires toe out and the driver swaps ends without even knowing what happened.

The stock C4 only has a few inches of usable suspension travel (in bump) to begin with. If you use up three inches in lowering it then that doesn't leave much for your suspension to do it's thing! The results, however good they look, could be evil in the handling department.


[Modified by speedjohnson, 7:12 PM 6/23/2003]

 

So if I cut my bumpstops off will that solve my problem? Thanks for the info, This is what I need to learn. I wish this thing rode like my c5 that was lowered 3.5" :chevy :thumbs:

 

I just left WCC and told them to CUT OFF the bump stops. Hopefully this will get me some suspension travel back. We'll find out tomorrow. :cheers:

 

I've thought about it and read a lot, but have not gone to coil overs. I've read & heard that the Koni bodies (Yellow SAs at least) like I have are too thin to groove for coil-overs.....

 

Did the machine shop groove the shocks while they were still charged/pressurized? I have been thinking about grooving my Bilsteins as I've got a lathe here in my shop. I just don't want to cut too deep & ruin the shock. My Bilstein's have a 1.985 outside diameter, what OD were your Bilstein's? What inside diameter threaded sleeve kit did you use? The kits I've looked at have a 2.040 ID which would leave about .027 per side clearance between the shock & threaded coil-over sleeve.

 

I called Jack at Bilstein America (West) from the contact number on their website. He gave me specifics for min/max ID, groove width, etc. I can't find my notes, but it came out to around a .030 deep and .55 wide groove. Call him for more exact #'s. Yes, the shocks were cut while still pressureized.

 

Thanks Speed, I've spoke with Jack out there before on the "Moracca" valved shocks. I'll call him in the morning. :cool:

 

Can bilstien just do the coilovers for us guys?

 

Now I'm a little nervous about you just cutting off the bumpstops and slamming the rear of that vette ... I want to be clear ... and not give you any bum advise ... I don't want you to ruin your new shocks or take a wild ride backwards because your suspension bottoms out and your rear wheels are steering by themselves.

Do this for me: Put the car on jackstands and remove the rear spring. Remove the dust boot or steel cap off your rear shocks and reinstall. Jack up the wheel until you get the ride height that your after. Measure this. Then jack the wheel up until the shock bottoms out and record the measurement. **Note that this cannot happen when driving or it will ruin your shocks.** Something must be done to avoid this: either gain some extended spring travel by moving the top shock mount up, a rubber bump stop can be put on the shock rod or a modified frame bump stop must be incorporated to stop the suspension from bottoming the shock rod into the shock.

Then check to be sure that you have at least 2 inches of suspension travel from rideheight until the shock bottoms. If you don't have suspension travel then you will need to either raise the car until you do or move the shock mount up (cut it up into the frame tube and reweld.) If you bottom out the suspension (like under hard acceleration off the corner) the suspension will become rock hard and you will loop it (ask me how I know!)

Now that you've got the thing really slung low and have adequate suspension travel you must realize that the control rod angles have changed (half shaft is the upper and the camber rod is the lower) ... they have gone from a slightly declining angle outward towards the wheel (stock rideheight) to now a flat or even an upward slant. You have lost the "sweet spot" in the suspension arc. In other words, now, when the arm goes thru it's arc of travel up, the distance between the two points it controls becomes relatively shorter. You can show this to your self by drawing it out on a peice of paper. What this means to your independant rear suspension is that when your lowered car goes thru bump the wheel moves quite a bit further inward (than on a non-lowered car), however, the toe rod is set up for a stock ride height vehicle. The result is that the rear wheel will turn when it moves into bump, just like someone has put a steering wheel on the rear tires. To fix this you must buy an adjustable toe rod and shim the outboard link up 3/8 to 1/2 inch ( it's best to set this up with a bump steer plate). You can get these from DRM, Exotic Muscle or Guldstrand. speed

 

ok guys all the help was A+. I went ahead with the QA1'a in the front with a 350 lb/in. spring. I bet i will run a rate closer to 450 in due time. However, I do need to get a few more sway bar bushings, bump steer kit in the front, toe rods in the rear and maybe new ball joints. With my CCW's and new Michelins this car will be a slot car by summer's end. Thanks a million.
Cheers,
Robert

 

My caris severely lowered too. I recomend going with a stiff spring and sway bar because of the limited travel. Cutting the bumpstops will help but you dont want to hear what it sounds like when you go over a huge bump. or see it either. Ive seen too many cracked knuckles already...

 

ok, I got the HAL QA1 coil overs and they are works of art. I have yet to install them but marvelous build quality. As I said before, i am using 350# springs and Z51 sway bars. I think for the street this is adequate but only trial and error will tell the truth both on the street and track. Where are you guys getting your ball joints from?
Cheers,
Robert

 

Well I just found out today how it sounded and my butt puckered up REAL QUICK. The fact of the matter is that the FX3 on my 96 is a complete JOKE. The rear spring is so friggen soft it belongs on a oldsmobuik. I had them raise it until I can order the coil overs. The new mechanic at the shop said he has done alot of them and says he can modify the bumpstop/frame to compensate for lost suspension travel. All I know is the car floats because of this moranically soft spring rates. What is the MAXIMUM spring rate you have heard of on these cars? The mechanic says the NEW SCHOOL way of doing it is softer springs with harder valved shocks. All I know is something will be ordered here shortly. :confused: :crazy: :U