moespeeds

In extended high G turns I'm getting a banging from the rear of the car, like a hammer blow. A friend told me it's the differential and it's normal. The car doesn't upset or lose traction in any way. So far I've noticed it in very hard extended right turns when I'm hard on the gas. It's not constant or consistent, seems random but only in hard turns under power. I'm running Royal Purple 90w Diff with no additive. '00 FRC LS1. Is this normal?

redtopz

I don't know about the diff making a noise like that, but your rear sway bar could be popping from one side to the other in those conditions.

sperkins

No.
Have you checked to make sure nothing is loose in the suspension?

Olitho

Check for cracks in the hub around the center of the flange.

It will make a deep loud twanging bang when it is cracking/cracked?

Also check for cracks in your wheel spokes although that is a much more subtle and high frequency tapping sound.


Oli

AU N EGL

also check your bearings.

moespeeds

No cracks, no loose suspension, bearings are good, sway bar looks good. I should have included that in the OP, when I heard it the first time I took the car to the track, I went over everything under there with a microscope. When I went to VIR, I never heard it once all weekend. First time was at NJMP Thunderbolt, in the long right hander. Last weekend I was at lightning, and same thing in the long right hander going under the bridge. Only in high G turns when I'm hard on the gas.

argonaut

I occasionally have exactly the same noise on high G right hand corners. I have gone thru all the nuts on the suspension, sway, etc. several times. I have even disconnected the sway altogether and the noise will still occur. I have replaced end links. I have checked wheel bearings and they seem fine. Its been doing it for several years now, only on high speed rights and only on occasion. At Thunderbolt the last turn before the front straight is where it occurs most often. Never heard mention that it could be the diff before. My car has LG colilovers and I've been assuming it might be interfearance between the sping coil and the tie rod.

argonaut

At Thunderbolt is that the right heading into the octopus or the right onto the front straight?

RX-Ben

The endlinks may be hitting the rear tie rods if your sway bar moves laterally in the mounts.
You should be able to tell if you will have a problem with the coils by jacking up the rear spindle with the tire off.

Cobra4B

Could just be the tires chucking a glob of rubber off. They usually come off at high speed and make a loud bang as they hit the wheel well liner.

pewterhdtop

Cobra4B nailed what I have experienced with my C5 FRC, mostly occurs in the high G turns, many times it is the pick up rubber parting ways with the tire into the wheel well.

UstaB-GS549

Same here. Track turds. Just one corner at GingerMan. Happens every time that I run there.

sperkins

Happening here at the :20 sec mark and the 2:08 mark. Skip through the rest. It's all pretty boring.

froggy47

Just a WAG but my buddy picked up a CTSV and had a banging noise on hard shifts & it was some internals in the diff. He found later that the ctsv diff has a weakness in it.

I know it's not exactly the same diff, so just putting it out there as a data point.

Hope you track it down. Doesn't sound like a track turd to me. Sounds metal.

2 GTOs

I get it at 9 and sometimes going onto the straight as well. I always assumed it was some thing shifting.

CP Thunder

Check your rear diff bolts.........ask Chris Ingle what it sounds like when the diff is going side to side in the car. He didn't find it until he put a GO PRO under the car (IIRC).

Bill Dearborn

I had a clunk in the rear of my C5Z that I searched for for a couple of years and never found. It sounded like something sliding sideways inside the rear frame rail and would happen on either left or right hand turns.

Bill

VGLNTE1

yup

SteveDoten

I've never seen and it's rarely posted, there was a TSB from 10 years ago concerning a part of the FRC frame coming apart; don't have the details, IIRC is was the sheet metal skin near the tanks

.........GOPro under car is a good idea

Cobra4B

Hmmm... have a link to that TSB? That's one I've never heard of. I did see another one I'd never heard of that Bill Curlee posted where the rear upper shock mount weld was failing.