I am trying to figure out, if I should replace my clutch and flywheel in my 52 chevy truck, or if it may just be a bad throw-out bearing or pilot bushing. The clutch was replaced only about 20K miles ago. I started hearing a growling and squealing sound with metallic smell, only when under load and driving forward or backward. When I press the clutch pedal down the noise goes away. In neutral I can rev the engine and no noise. I think a bad or dry throw-out bearing only makes noise when pressing the clutch pedal down. But my clutch disc should not be worn that soon?
From what you have described I would suspect the output shaft bearing in the trans. Are you sitting still or driving in neutral when you rev the engine? Is the clutch pedal up or down? If you are in neutral (engine running) with your foot on the clutch, sitting still, the disc and input shaft (and therefor no part of the trans) are not turning. In neutral (engine running), sitting still with your foot off the clutch, the flywheel, pressure plate, disc, trans input shaft, cluster and speed gears are turning, but not the output shaft. When you are driving put it in neutral and push the clutch in. A bad output shaft bearing noise will still be there but should diminish. If it is the cluster bearings or the rollers in the back of the input shaft, any noise from them should go away or diminish in third gear (3 spd.) because you have taken the load off the cluster and the input and output are now turning at the same speed. If the clutch is slipping, check the linkage for binds and adjust the toe play, Also check to make sure all the pressure plate bolts are tight and there are no broken fingers. Your assessment of the throw out bearing is one of those 99.9 per-centers. Another possibility is the 'U' joint in the front of the torque tube.
Thanks for your reply. Your descriptions start to makes sense now and point more towards the output end of the transmission. I can confirm more symptoms... Clutch feels fine and doesn't slip (engine does not rev up in speed) When I rev the engine in neutral, it is quiet and no low-mild-rumbling vibrations regardless of rolling or sitting still. Also regardless if I push the clutch in or release. And then this, probably telling clue: The low rumbling is stronger when driving in first gear and second gear. It gets less in third gear and that's why I felt comfortable driving home the 20 mile road trip with hardly stopping or shifting. Then the next morning backing out of the garage and cold 40s temps in February, I could hear the metallic grinding high pitch squeal all the time when under load then going into first and second. I turned around back home and parked it. Now the temps are warmer to work in the garage and I want to get into it.
A fluid level check would also be in order. From your description, though, at this time it is probably a moot point.
I top it off every 1000 miles, as per manual recommendation. 1500 miles at the latest. That's why I didn't suspect the transmission at first. When the noise started, I was at 700 miles since the last top-off and topped it off after getting home with the usual amount it needs. I use GL-4 rated gear oil because of the brass parts. Then next cold morning it sounded like this had no influence and it now was a steady bright dry metal-to-metal squeal, under load only.
Interesting - I am not sure at what point of the pedal travel the noise stops. But I know the moment the clutch pedal relieves the load, the noise stops.
I asked because I had a 37 that would growl under load. if you just pushed the clutch a little bit it would stop. I can't remember exactly what was worn but the fingers were coming too far back.
It is more like you have to remove power from the engine interacting with the transmission so the noise stops. But the drive line behaves just fine, if you would want to ignore the noise and faint metallic rubbing smell or just don't know any better.
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