I put this in the autocrossing forum but thought I'd double here since it's not necessarily a problem specific to that, and I figure more people are in this forum.

I went autocrossing this weekend ('98 coupe), and there were both right and left hand sweeping curves. Going left, I could drive at the limit on the tires to where it was just sliding, no problem. Going right, I got some pretty bad wheel hop on the right rear. Even the corner workers saw it and said it was hopping. As I got to a certain point (g force or whatever you want to call it), it would start doing it. Would this be a bad shock, diff issue, or could it be something else? I can go in circles both ways with no chatter. Diff lube is AMSoil severe gear and is at the right level. I took a look underneath and when I pulled the wheel off, and I don’t see anything wrong/loose, or the shock leaking or anything. I bounced both rear corners and they react the same and don't keep bouncing when I let go. The car seems to drive fine otherwise. Any ideas?

 

You need to provide more data:

1. Miles on the suspension?

2. Miles on the current shocks (what type shocks)

3. C5 Suspension type (i.e. FE1, F-45, or Z51)

4. Auto or MN6?

In my honest opinion, its shocks if you still have stock shocks.

Examine the rear spring perches and make sure that your spring is not delaminating or damaged.

Make sure that the sway bar bushings and end links are not damaged (twisted and bent if plastic)

I up graded my 02 ZO6 shocks to C6 ZO6 shocks and solved a severe rear end control issue that I had when entering high speed sweeping turns (right direction)

The rear end would start skiddering across the road if the road was the least bit rough. Talk about a butt pucker moment!!

The new set of four C6 ZO6 shocks completely resolved that issue. They fit like STOCK!

I'm about to change out my rubber stock bushings for poly bushings. Your 98 bushings could be pretty worn so recommend checking them.

Also check the rear wheel bearings and make sure that they do not have excessive slop/lost motion when you push pull at the 1200/0600 and 0300/0900 positions

How are your differential limited slip clutches? If you put the trans in neutral and jack up one rear wheel so you can rotate it, you can check the health of the clutches. It should take some force to break the rear wheel loose so you can rotate it. A new set of clutches will be above 100 ft/lbs to break away. As the clutches wear, that break away force becomes less and less. If the preload Belliview washers crack or break, the preload will go away and it will be very easy to rotate the raised rear wheel against the stationary wheel

If it's very easy to turn,, time for a replacement set of clutches and belliview washers. Check out the post provided below as it will help you understand the inter-workings of the differential:

- C5, ragtopws6 , Upgrading your C5 rear with C6 Z06 guts, : http://forums.corvetteforum.com/c5-g...-z06-guts.html

- C5, Its_Go_Time, Output Shaft Install - Left and Right: http://forums.corvetteforum.com/c5-t...post1573407966

 

135k on the car, but I did hit the RR wheel a couple years ago (autocrossing and hit oil...not out being irresponsible) and everything suspension that was either on the right side or shared between sides had to be replaced (and you think YOU had the butt pucker moment...). So the left shock has 135k and the right one I'm not sure as I had used parts put on except a new RR wheel bearing assy. The car is an F45 suspension car with manual trans. Sway bar links were replaced with metal ones.

I gave it a look underneath and didn't see anything wrong, but I'll give it another check and also check the clutches as you mentioned.

 

Well,,,,,,,,,,,,, Being a HATER of the F-45 suspension (YES I HAD It on my 98 coupe) all I can recommend if to GET RID OF THAT CRAP!!!

Some people swearer by it but,, If you ever drive a C5 with a purpose built performance suspension (Z-51 or ZO6 or aftermarket ) you will NEVER LOOK BACK!

The F-45 only came with the BASE FE-1 SUSPENSION. So, at this point,,,,,,,,,,,, any thing that you do will be an improvement.

If it were me, I would look for a used C5 ZO6 or Z-51 set up,,,, Springs, sway bars and end links and add the C6 ZO6 shocks. You will be AMAZED with the difference in handling!!!

You can also contact Gene Culley @ www.gmpartshouse.com and get his C6 Suspension UP-grade. Give him a call and discuss prices.

Bill

 

F45

 

LOfuc^% LOUD ,, You must have expierenced one firsthand~~

 

mine has the Z51 but I have driven one and who ever thought up that should have been canned!!!

 

Just did the one wheel in the air spin test, and with the longest moment arm possible (i.e. putting a torque wrench on the lug nut at 3:00 on the right side and pointing the wrench toward the front) the wheels spun at about 35-37 ft lbs.

 

That sounds pretty low, it should be up in the 200 ft lbs range when measured from the axle nut.

 

Great info in this thread! I'm about to put all the c6 z06 internals in my c5 m6. Anyone know if a c6 a6 case (already have one) will interchange/bolt in the c5? Will a a4 case work or is the 3 rib best option? I will be using the dte brace.

 

The spec for the C5 diff is 75 lb-ft. C6 is ~120 lb-ft I believe.

For the OP, sounds like you might need new diff clutch plates (e.g. a diff rebuild). That said, you might have other problems as well, but your diff should be putting about 75 lb-ft through the limited slip diff. Unfortunately, that is one of the many weak links in the C5 when used in demanding applications like the track. Most of my fellow SCCA touring racing buddies change diffs fairly often. I just had mine rebuilt last weekend after six years of use.

 

What does it run to get a diff rebuilt? Looks like you have to take half the car apart to get it out.

I also talked to a GM world class certified tech, and the first question he asked me is what lube I used in the diff. He gave me a good scolding for using AMSoil and said only the GM lube should be used, and that he's seen a lot of diffs come in for service due to incorrect lubrication (and this is not a local guy, so wasn't trying to sell me anything). I also called a couple places here that specialize in Corvettes and was told basically the same thing. One guy did a lot of late model prep for guys who track, and he said all he ever uses is GM, and he's never seen a problem in those cars. Oops.

 

Well,,,,,,,,, I can tell you,,,,, ANY rear-end lubricant that MEETS or EXCEEDS GM specifications,, is NOT going to cause damage to the rear-end. AMSOIL is an excellent product. It most likely EXCEEDS the GM SPEC and has the correct limited slip additive. \
Contact forum member " SUBDRIVER " and he can give you the scoop on any AMSOIL Product.

People that add differential lube WITHOUT the required amount of LIMITED SLIP ADDATIVE will for sure have clutch plate issues.

Your rear-end isn’t TOAST,, The clutch packs are just worn and/or you have broken clutch pack springs. I’ve checked more than I can count clutch force readings and ANY C5 with more than 60K miles is going to have weak clutches. Its just part of the wear and tear game. Every time you turn LEFT or RIGHT, those clutches slip and any type of slippage causes wear. The limited slip additive allows the clutches to slip at the correct force. Without that limited slip additive, the clutches would chatter and bind when you make a sharp turn.

The clutches that are really weak, have BROKEN BELLEVIEW spring/s NO lubricant GM or aftermarket will prevent that from happening.. Just a poor designed part from GM for the C5. They break. Ask ANYONE that services C5 rear ends. The springs were redesigned for the C6 and are a little more robust. The clutch packs were also redesigned and are also more robust. The C6 clutches , springs and output shafts are a direct fit improvement for our rear ends. You can do the up-grade at home in your garage. If your rear-end isn’t howling or making ugly noises, just doing the C6 refresh will get you back on the road with minimum cash outlay.

Look at the post I provided.. It shows broken springs. If they break in more than one area, the small piece will work out of its cavity and damage bearings or gears.
Bill

 

Bill, it's Belleville washer or disk spring.

 

LOL,,,, Yep,, that’s just one of those words that no matter how many times you see it spelled correctly, when you go to re-spell it, it encrypts itself. I gave up trying to spell it correctly and just take the beating!

Belleville, Belleville, Belleville, Belleville, Belleville

Hand Slapped and spelled it five times!