C4 Transmission Knock
Thread Starter
3rd Gear
Joined: Jun 2012
Posts: 3
Likes: 0
C4 Transmission Knock
I have a 93 C4 with an automatic transmission, it has recently started to make a knocking/clicking noise under the car at idle. I got under the car and it sounds like the noise is coming from the rear of the tramnsmission. But I cant really tell. I can hear it at idle in park, and even when in gear. When I rev up the engine it seems to get faster, but I dont hear it while driving.
Any suggestions would be greatly appreciated.
Thanks,
The new Guy
Any suggestions would be greatly appreciated.
Thanks,
The new Guy
Thread Starter
3rd Gear
Joined: Jun 2012
Posts: 3
Likes: 0
trans knock
I have pulled the dust cover for the convertor off, and everything looked to be in order. I know that transmissions usually dont knock, but the noise seems to be louder near the transmission yoke.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
When you're in Park basically the only things moving in the trans are the torque converter and the pump. The output shaft and everything associated with it is stationary.
I vote for exhaust leak.
I vote for exhaust leak.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Flywheel; bolts//TC bolts....rear main end play....crank walking in/out. Mine also does this on occasion. It can be heard inside the cabin but not outside unless you get under the car. Noise goes away the instant that rpm increases. Its more of a bumping/knock and not a beating or hitting sound...rubbing/bumping? difficult to describe. Everything that I've looked into says TC bolts, or crank. It may not do it for weeks at a time then suddenly it starts again and may do it for one run cycle and quit...or it may go on for days.
So far, nothing weird or broken. Its been several years now...
I did have a starter explode and send chunks of dead starter housing into the flywheel once...the engine was running high rpm and chunks beat around like a steel pipe against a metal trash can. Cleaned it all out and inspected. The noise appeared some time after that incident...intermittent at best.
So far, nothing weird or broken. Its been several years now...
I did have a starter explode and send chunks of dead starter housing into the flywheel once...the engine was running high rpm and chunks beat around like a steel pipe against a metal trash can. Cleaned it all out and inspected. The noise appeared some time after that incident...intermittent at best.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Unbolt your torque converter from the flex plate. Push the converter back into the trans. Check the gap between the torque converter mounts and the flex plate. The gap should be 1/8" or less.
If it's larger then you need to add shims (thick washers -- must all be the same thickness) between the torque converter and flex plate to push the torque converter back into the pump where it belongs. You probably need longer bolts too. Be careful that they're not so long that the ends touch the torque converter. They need to be metric grade 10.6. They need Locktite.
If it's larger then you need to add shims (thick washers -- must all be the same thickness) between the torque converter and flex plate to push the torque converter back into the pump where it belongs. You probably need longer bolts too. Be careful that they're not so long that the ends touch the torque converter. They need to be metric grade 10.6. They need Locktite.
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Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Regarding the knocking/bumping rotating sound....
Mine still does it on occasion but its not consistent. Might go months and not hear that. Then when hot in gear at idle it sounds link a muffled bumping of something rotating. Not a knocking more of bumping...if that makes any sense. Any increase in rpm and it vanishes.
My best guess is still torque converter bolts or crank walking in/out. Might only be .005 but something is moving around...
Race Director
Joined: Apr 2003
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From: moraga ca