Clunking noise from the rear end???

[Chris_32212]

August 20th. I drove her down to PIR and everything was fine. Got to the burnout box for the first time and started to heat up my Summitomo HTRZ rear tires and I felt the rear end make the usual drift to the right because I don't have C4 beam plates yet. But during the burnout, I felt something break. The car snapped sideways about six inches further to the right and stopped as if the body of the car hit something (which of course it didn't).
I made my pass very gingerly and got back to the parking lot and jacked the car on both sides and could not feel any play in any drive shaft or half shaft. Could not feel any play in any of the suspension components. Yanked on both wheels in all directions with the car in the air and could not feel anything out of the ordinary. I decided to drive the car home where I could take a closer look but slowly got it up to free way speed without anymore noise or other issues. I have a spare six speed corvette parts car at home so I got on the throttle harder and harder but everything seemed fine. Go ahead and feel free to cringe but I took the car back and raced it more than ten more passes at PIR. I felt and heard a "clunk" several more times from the rear of the car throughout the night but it never broke. I ran 12.6 @ 114mph multiple times and drove it home. Turned into the driveway which was a tight, slow, right hand corner and heard it clunk three or four times. Clearly there is something that needs repair but I had to head out to Eastern Oregon to help my parents out and heven't had a chance to look at it since. Any ideas? On the way home, I went over several speed bumps with no nothing noticably wrong with the supsension. I would think that anything in the drivetrain that would be causing the car to make that much noise from the rear would have broke with the amount of extra abuse that I put on it. So the only things I can think of that might be causing it would be a wheel bearing or something. It shimmies a little while turning but still goes in a straight line pretty good. Penny for your thoughts???

[tccrab]

Just guessing, but my thinking is that it could be as simple as a U-Joint gone bad or as ugly as problems in the differential, i.ed, broken spider gear or clutch pack.
I've never broken a spindle so I don't know what the symptoms are, but I've read they are a weak point.

TomC
'Crabs

[Jagdpanzer]

Sounds like either a spider or side gear in the differential unit has split a tooth.
I would definitely tear it down and check it out thoroughly otherwise you run the risk of wiping out the gear set and differentila case when it finally lets go.

[tomtom72]

Okay, my two cents, fwiw.

On my C3...waaaay back in the late 70's before synthetic gear lube the rear would start to make clunking noises as the fluid lost it's lubricity when taking slow corners. Further lube degradation would eventually yield a loud banging noise from the clutch pack. Have you checked the fluid level and or do you know when the last change was performed? You could feel the rear slewing the car to the left or right randomly, and this symptom would get worse as the fluid degraded also.

A second thought, but this is way out in left field, are the C-beam bolts at proper t/q spec?


Tom

[rhipsher]

My money is on a toasted U-joint. Mine made the same noise also. Put new U-joints in and no more clunk. Your going to go through U-joints pretty often when you drag race. It just comes with the territory.

[Chris_32212]

I just got home 30min ago from eastern oregon. I will take a look at the differential fluid later tonight. The car does have a very noticiable "slweing" from left to right in conjuction with weird noises. I am probably going to replace all my u-joints and the diff fluid and take it for a spin and see if the problem has corrected itself. Thank you guys for your input.

[sammy]

chris if you do the u joints use the 799 series spicers they are the best money can buy

[USAFPILOT]

my car is making the exact same noise. Rick and I are going to replace the u-joints and hopefully that solves it. The U-Joints aren't to pricey, so if I am going to throw some money at a noise then they make perfect sense. I also think my problem began after doing some burnouts and drag racing.

[Chris_32212]

I got a tip from a friend here on the registry to go with the spicer differentials from dennys driveshafts. Not sure if they are the ones you recomended but Here is the link for the half shaft u joints i ordered. I also bought the drive shaft u joints too and parts are on their way. I also bought a poly bushing kit for the car and that is on the way too. http://www.dennysdriveshaft.com/p443...build_kit.html

It is somewhat comforting that my car isn't the only one having this issue. keep me posted on your situation.

So far, I have only gotten the exhaust out of the way. I pulled the bottom differential bolt last night thinking that would drain the fluid from the diff but it didn't. I am thinking since I have C4 beam plates ready to go in, a bushing kit on the way, and a spare 3.45 geared Dana 44 ready to go, I am going to pull the bat wing out today and split the differential case and have a look today. Thats a little ambitious, don't know if I will get that far but I will keep you guys posted.

Chris

[Chris_32212]

I ran out of time today to pull the diff, Should have it out pretty quickly tomorrow morning though.

I was talking with my dad who test drove the car several days ago to see what he thought of the issue and he told me that he backed the car down the hill out of the driveway and stopped, pushed in the clutch, and the car rolled "UP" hill... that sounds like something is binding up in the rear end to me and makes me highly doubt the issue is being caused by a U joint (but new u joints wont hurt a bit). I have a 3.73 gear dana 44 installed in my project car so I am going to pull that pumpkin and put that in the Z. That will get rid of my problems for sure and give her a little more pep. Then at some point I will rebuild the diff that is coming out of the Z with 4.10 gears for the project car. Will let you know what I find tomorrow when I pull apart the suspected bad differential.