LouisBarton

I fought the clunk and the clunk won, I fought the clunk and the clunk won.

Got the vette back today after control arm bushings replaced with Prothane, and after hubs cleaned and regreased by GM master mechanic wwho knows vettes. The clunk is still there. Now it only comes when I come to an aggressive halt; it is the last sound after I come to a complete rest. For review, All U joints replaced, shafts balanced, diff rebuilt including side yokes, new brake pads and rotors F and R, torque arm torqued down. Which leaves us with the rebuilt trans with performance shift "upgrade" for firmer shifts. Rebuild has only 25k miles on it tops. My best assessment at this time is that the clunk is a side effect of having the "upgraded" transmission. Any opinions on this?

Bob Hovey

Louis:

First, thanks for reposting. I've been chasing this "clunk" bug for awhile now too. But you have definitely taken a lead in solving it. One question, when you drive your car, do you drive it in D (3rd) or (D) 4th? When I have my shifter in D (3rd), I always get the clunk just before the car comes to a stop just like you said. BUT, when I'm in (D) 4th and come to a stop, NO CLUNK. Someone on the thirdgen.org (yup, I've been out there and they (700R4 guys) have the same problem. Someone on the thirdgen.org forum said it's normal for a 700R4 to bind when it downshifts from 3-2 when you have it originally in 3rd.

PS- as far as I know, my transmission has not been "upgraded", it's stock.

What do you think?

Bob '87


[Modified by Bob Hovey, 5:39 AM 10/23/2001]


[Modified by Bob Hovey, 5:40 AM 10/23/2001]

Mr Mojo

Could it be the torque converter?

miker61588

mr mojo could be right my torque conveter bolts became loose and started clunkin

nickd

Try the transmission mount?
the clunking sound is probably coming from a broken trans mount. It's an easy fix, $20 for a new mount and about 15 mins of labor.



[Modified by nickd, 8:19 AM 10/23/2001]

LouisBarton

I always drive in (D). I'll try it in D today. The only way that i don't get the clunk is to come to a very slowwwww stop. Even then, I can convince myself that I still faintly hear it. The concensus of the Local mechanic gurus is that the sound results from binding somewhere in the driveline.

$20 sounds good for a new trans mount . That'll be next. That will also be delayed awhile because we're going to Bowling Green tomorrow to tour the plant before the tours stop. It's nice to be able to get off work on a moment's notice. :D

nickd

Does it also do it during hard acceleration as well ?
Next time your at a stop light nail the gas, if it does it then I can almost gurantee it's a broken trans mount.
You can check pretty easily by getting under the car and putting a jack under the trans.

BBA

Ok, try this: Place the trans in manual low ( 1 ), and accelerate to about 15 mph, then stop while leaving the trans in manual low.

If the clunk is gone, then what you can be feeling is the trans downshift to low gear on coastdown. Normally, the 700R4/4L60 does not have a problem with it, but worn seals and or worn clutch packs can and do cause problems like that ( expecially common on Chrysler trannies, but all are susceptible ).

If the clunk is still there after trying that, it is not trans related, but chassis related. Check all weld seams ( front shock tower connector welds also ). Basically, it could be all weight shifting to the front is flexing something, then the complete stops would let it return to normal position.

BBA

The c4 does not use a tranny mount.

Bob Hovey

BBA - Thank you :smash: I spent a ½ hour on my back, light in hand, looking at the tranny for something called a tansmission mount. I was not not sure what it looked like, but I could not find it. Because C4's don't have one?? DOH! Also, I will try the stopping in 1st suggestion. I am almost positive I've tried this before and did not hear this clunk noise. I suspect what the Camaro guys say and that is the tranny binds when you have the shifter in 3rd D and it downshifts from 3-2. Although Louis said he drives around in (D) :confused:
Maybe I'll just turn the radio up loud and not listen anymore :lol:

Bob




[Modified by Bob Hovey, 8:44 AM 10/24/2001]

TrplBlk01

I have posted questions about this and there seems to be no one with any good explaination for why it happens. I had the tranning rebuilt last month and the guy at Performance Trans told me this is common with this trans.... I have the car now and the clunk is still there even after rebuilding the trans.

LouisBarton

:nono: You had me going with the trans mount. It didn't hit me until the second cup of coffee. There is no trans mount or insulator or other named item. I even double checked it with GM home office. The only trans mount is the Torque arm which has already been retorqued with the diff redo. I notice the clunk also when going in reverse and stopping so I don't believe it's a downshift issue but hey I'll try to test just about anything at this point. Mr Kinnebrew doesn't mention this in his little C4 book. Has anyone asked him? Carlisle maybe?

nickd

Louis,
I apologize for that, it reminded of the broken trans mount I had with my Camaro a couple years ago and for some reason I tend to revert back to that setup, I had the car so long sometimes I forget I have a C4 now.
In my defense, it was early and I didn't have any coffee :nopity