Clutch Issues

[z32chick]

1974 620 - l20b swapped w/ FS5W71B 5spd transmission

 

Everything has been working fine for approx 500 miles since the rebuild.  However, leaving a car show a couple weeks ago I noticed a howling sound coming from the transmission area when the clutch was depressed.  It happens in gear and in neutral and does not occur every time I press the clutch.  It's usually worse when cold.  The clutch engages fine and stops the whine/howl as soon as it's engaged.  

 

Does anyone have an idea of what I should start looking at?  If you need a video of the sound I can get one tomorrow and post it.

 

Thanks in advance!

[datzenmike]

If it only makes this when depressing, holding depressed or raising the clutch pedal then this is the release bearing. The rest of the time it is not moving even if the truck is. When you swapped in the 5 speed did you replace the release bearing? You should always do this. Unfortunately the only fix is to pull the transmission out to get at an replace it.

 

 

[z32chick]

That was my fear.. I installed a new collar w/ bearing when I replaced the transmission though 🤷‍♀️

[datzenmike]

 

 

Did you pack the cavity inside the collar with grease? It does slide along the nose covering or the input shaft. Grease the pivot ball where the clutch arm seats, where the slave push rod contacts the end of the clutch arm? I doubt these are the cause of the sound but they need grease to reduce wear over time.

 

 

Was the new collar exactly the same as the old one or was it included with the clutch kit? Release bearings should last a lot longer than that so if the collar is too long, the clutch arm would extend the bearing against the clutch diaphragm fingers and it may be spinning all the time and possible under load also. Like driving with your foot resting on the clutch pedal.

[Stoffregen Motorsports]

Replacement release bearings often have a different profile on the surface that touches the clutch cover. This is because there are two variants on the clutch cover fingers - straight and curved. If you accidentally installed the wrong bearing, it could make that noise.

 

Even if all the clutch parts came in the same kit, it's possible the bearing was wrong.

Edited December 26, 2022 by Stoffregen Motorsports

[z32chick]

I greased everything up during install and honestly don't remember which collar I used, because I did have (2) different ones to choose from.  I'm pretty sure I used the one out of the original 4spd transmission based on advice I got here.  We'll see how everything looks when I open it back up.

[datzenmike]

If you didn't replace the clutch then you should use the original release bearing collar as they are a matched set. The collar never wears out.

 

If another collar was purchased then this throws a wrench into the works if it was used instead. It's unknown if it's exactly the same and that's the problem. If it's slightly longer the bearing may be riding on the diaphragm fingers and will be spinning constantly for the last 500 miles. I reduce the wear on the release bearing by slipping transmission into neutral at stop lights and letting the clutch up. (this also relieves the wear on the thrust bearing on the crankshaft)  The applied clamping force of a '74 L18 pressure plate is 550Kg or well over 1,200 pounds. That's a lot riding on that bearing.

 

The collar part number is 30501-N1601 see chart below for dimensions....

 

 

FWIW the release bearing part number is 30502-21000