Noisy 4 speed tranny

[bobs77]

Guys,

Just took my '77Z on it's first long trip (400+ miles) since I bought it 4 years ago, and outside of a little oil pressure fluctuation it ran fine. I started it up this morning, put it into reverse and started to back out of the garage when I heard a loud whine and what sounded like a metal-rubbing-on-metal sound. I shifted into 1st and pulled it back into the garage. The sound ended when I shut the engine off.

I went out again a couple of hours later to check it out and see where the noise was coming from. I got the following:

--I heard the noise only when the drive train was cold

--even when cold it doesn't happen all the time

--with the engine idling and clutch depressed, I shifted into 1st and 2nd without any noise. I shifted into 3rd and 4th and the noise came back

--when it's making this noise I can feel increased vibration in the shift knob

The car has 65000 miles and as far as I know the tranny is original; the only work done was a clutch replacement by the PO a year before I bought it.

Does this sound like a tranny bearing failure?

Thanks,

Bob

[Arne]

Let me get this straight - while parked and the clutch pedal depressed, it makes the noise in third and fourth gears, but not in first and second?

Sorry, this doesn't compute. If the car is stationary, the pedal is depressed and the transmission is in gear (any gear), there are no parts moving inside the transmission. So there is no possible way that the transmission bearings could be making this noise since they wouldn't be moving at all.

My guess is that the throwout bearing is bad. This could account for your symptoms. If the clutch is adjusted properly (with a small amount of clearance at rest), you should only hear it when the pedal is depressed. However, if the clutch is mis-adjusted and the bearing is slightly contacting the pressure plate fingers all the time you would get varying levels of noise all the time.

[bobs77]

Good point Arne.

I verified the noise last night--with the engine running and the clutch pedal depressed I shifted into each gear. When I shifted into 4th I got the same noise. I tried several times after that but the noise didn't come back. Seems to only occur when everything is cold.

However, if the clutch is mis-adjusted and the bearing is slightly contacting the pressure plate fingers all the time you would get varying levels of noise all the time.

I think you're right that the problem is in the clutch assembly, but I'm not getting noise all the time--the clutch is quiet except for this occasional noise. I'll check the clutch adjustment next. Thanks for the help.

[240ZX]

I'd have to agree with Arne's analysis.....throwout bearing! Those suckers don't last forever, especially if the clutch is improperly adjusted or if one tends to ride the clutch pedal.

Tom

[bobs77]

Sounds like a good possibility. The PO had the clutch replaced 7 years ago--no idea if the throwout bearing was changed then. I don't ride the clutch but no idea if she did. Or if it was adjusted correctly while she had it (I had it done about 4000 miles ago).

Thanks for the feedback.

[bobs77]

So this will be the first time I've pulled a transmission.....I have the FSM, but are there's always things it doesn't cover in much detail. Any helpful hints you guys can pass along?

[Bcalvosa]

It may sound basic, but before pulling the trans, try tightening the alternator belt (and A/C and air pump belts, if equipped). The symptoms sound more like belt squeal to me. You can also remove all the belts and briefly start the engine when cold to see if the noise goes away.

If it is the throw out bearing, the noise should change when you step on and release the clutch.

Good luck...

[Arne]

Bob, the post you just replied to was almost 3 years old. The issue is probably long finished by now.