RyanR0101

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?

froggy47

Most courses have different traction characteristics on each turn (except maybe air strip courses). It could be you had more/less grip depending on the turn. If your shocks are adjustable, I would have softened a bit to see if that helps.

Otherwise I would just watch for it on the next event & see if it reoccurs.

I know on straight launch if I do it poorly mine will axle hop every time & there is nothing wrong with mine.

RyanR0101

It's an F45 car, so that's the extent of the asjustability. And it seemed I could steer in and out of the hop, so I didn't think it was specific to that corner. Less steering or less throttle reduced the hop. I'll continue to pay attention to it, but it was just a bit freaky when it happened as I've never experienced that before.

froggy47

Here is a link to f45 stuff.

http://forums.corvetteforum.com/c5-t...-troubles.html

Did you check codes?

autoxer6

Ryan,
How many times have you run the car since it was repaired?
What was replaced?
Did you ever notice this before the repairs?

I think it is one of these:
Diff
Shocks
Suspension binding / alignment / problem.

I could loan you my stock 04 Z06 rear shocks to see if that eliminates the problem.

Chris Shay

RyanR0101

I've run it autocrossing three times since the repair. Only during the school in the east course on the right sweeper did I ever notice anything. Never noticed it before, but it's kind of a particular set of circumstances. I could back out of the throttle or steering to reduce or eliminate it. He replaced pretty much everything in the rear suspension that is either exclusive to the right side or shared. I did a few small circles both ways this morning and didn't get any chatter or anything.

froggy47

What was repaired? I didn't get that.

RyanR0101

A couple years ago I hit a pole with the RR while autocrossing, and everything on that side plus anything that was shared between sides had to be replaced.

froggy47

If you think all the above is working correctly, my only idea would to be drain the diff & try RedLine 75w90 gear oil (get the one that INCLUDES the additive). I've used it 30k miles.

C66 Racing

I'd check the diff clutch plates - they wear out faster than most realize.

The spec for the C5 diff is 75 lb-ft. C6 is ~120 lb-ft I believe. The C6 plates will fit in a C5 diff but they are about $300 a set.

To check the diff, lift one rear wheel. With the car in neutral and parking brake off, put a torque wrench on the axle nut of the axle in the air and measure how much torque is needed to move the axle. Should be about 75 lb-ft for the C5. Lower and you need new diff clutch plates. Could be something else as well, but this is something I check often on my car.

Most of my fellow SCCA touring racing buddies change diffs fairly often. I just had mine rebuilt last weekend after six years of use.