Help! Bottom End Knocking, only @ idle, only after car warms up.

[gmjunkie]

Thanks Hib for the stethoscope suggestion, I popped into Loews this afternoon to see if they sold any, nope. But I do have the tubing now.

Advance,Auto Zone,Napa ot'ta have one,I think I bought mine at Northern Tool!~!!

 

[EttevroC]

Advance,Auto Zone,Napa ot'ta have one,I think I bought mine at Northern Tool!~!!

, thanks!

 

[boomdriver]

:duh I thought I was dropping it off to a good shop, it's one of the highest rated Corvette Only shops in the DC area, but maybe I got a short timer for a mechanic that day. :cry

I've learned the hard way that NOT all Corvette shops are good, honest, reputable shops...some are just thieves waiting for easy money to be made off their customers. I met one like that in HOUSTON>> (hope they see this) about 11 yrs ago...
went to them with an a/c problem. They screwed around, claimed they found the reason the clutch did'nt engage, fixed it for several hundred dollars and sent me out the door. I was driving thru on a family crisis and had no time or place to work on it myself so they got it.
I got 10 miles away and the a/c quit. It was Aug in Houston...like the jungles of viet nam.
I drove straight back and they took the car back in.
New bill for another few hundred bucks...claiming there was a NEW a/c problem that was causing the exact same symptom. F'n manager held my car hostage until I gave them their ransom, then I left. I drive past that toilet operation with the big pretty signs everyday...and I drive across town to another (any other) corvette shop for work, parts, or just to hang out. This particular shop will never see another penny of mine...

Thats why I always advise folks to join the local Corvette club and hear it from customers and what they have to say. What a chicken s*** service writer says is only one lie short of being a politician.

Live and learn...

 

[joe paco]

:duh

I don't think it's the surface either,I think the fly wheel has some broken springs in it!~!! I was pointing out the Butcher Resurface job,It's plainly been ground unevenly by hand!(blow the 1st 2 potos up 150% and take a good look!)At best it has to be somewhat out of balance now!! That will amplify any other noises from broken springs or worn bushings in the duel mass that not necessarily were audible before!~!! I've been on a couple Duel Mass rodeos before,even changed out a cam and lifters over a noise very similar!~!!

I may be WRONG,
I have been before!! :L

I think you are right on this one. never knew the "vibration dampening" flywheel was in Corvettes. rpm moves the noise source, I guess? if you push the clutch in that might change it audibly. seems simple enuff' to do. Thanks for the post, junkie.
joe (the smiley should have been a "duh!")

 

[joe paco]

junkie, this is interesting: my Haynes manual lists one root cause for clutch-related noise in neutral, engine running.

"damaged clutch release bearing."

saludos

 

[EttevroC]

Thats why I always advise folks to join the local Corvette club and hear it from customers and what they have to say. What a chicken s*** service writer says is only one lie short of being a politician.

Live and learn...

You're absolutely right. Boomdriver

 

[helphos]

Had ya gone to a good trans shop they would have replaced the flywheel.....

I thought they didn't make dual mass flywheels anymore. I have a '93 six speed vert that I need to replace the transmission on, and I assumed I'd need a singlemass flywheel. (I'll be replacing a black tag with a Blue tag zf, but that's a different story!)

After watching the video (ZF video) it looks like you could rebuild it yourself if you could find the parts. :eyerole

 

[lozer]

I have the same car and the exact same issue. What did you find to be the issue?

 

[froggy47]

Push in the clutch pedal and see if it changes . Put it in gear and slowly release the pedal and see what the sound does.
You said you surfaced the flywheel. If it is OEM it has the dual mass flywheel. You may have a flywheel about to come apart. ZF doc told me the early flywheels had no cover over the seal in the flywheel crap can get in and take out the seal.Then things start to go wrong.
If it appears to be flywheel related you might want to contact him, he is very good about sharing information.

Scav.

BTW Before I replaced my clutch and flywheel I had a similar rhythm but more of a click when it was warmed up. That is gone. Did you notice a click before the knock started ?
I located this after I posted.

ZF dual mass flywheel

Really good description of how DM flywheel works, now I know why GM recommends to replace & not resurface.

Bet one of those springs broke because the new clutch put more torque on them.

My guess is the shop charged you for a resurface flywheel & just took a rotary wire brush to it & never took it out. Figured they could "get away" without replacing the DM.

I think your issue is right there clutch/throwout/DM flywheel.

Good luck.

 

[hsz33]

1990 base 6 speed manual knocking at idle after warmed up

Same problem Knocking sound at idle after the car has warmed up. mechanic suspects fly wheel issues, but my question is why doesnt it knock when its cold? shouldnt it knock constanly if something is cracked or loose? besides I heard the manual transmission flywheel is thicker than auto and its not broken easily. Hope I am not getting screwed by it being a loose maniforld or an exhaust problem. Main concern why after the car has warmed up?? Thanks. by the way the car runs great! just that sound is killing me!!! ad

 

[Schrade]

Welcome onto the boards there...

ZF is a NOISY tranny. Does the noise change at all, in gear, or out of gear, while sitting idling?

Probably should create a new thread, since this is an old one (after reading this one through, of course)...

 

[hsz33]

Ok Thank you. Only at idle. Also in second gear on up when i gun it i hear a low pich screaching sound and in first gear on downhill going slow with no breaks a loud grinding sound!