Transmission noise that came and went at start up

Started the car today from cold and there was an immediate grrrr noise from the transmission that lasted about 15 seconds and disappeared as soon as I pressed the clutch. Reminded me of the noise you hear when a shaft is running in a dry loose bearing. Releasing the clutch did not produce the noise again. That’s about the best I can describe it. I let it warm up a bit and set out on a drive with no issues. Noise has not returned. This is a rebuilt tranny with 600 miles on it.
Anyone have any ideas what it might be?

Pilot bushing (20 characters)

If the clutch was engaged (pedal up, not pressed) when you started it and you had the noise it wouldn’t be a pilot, if the pedal was down sure could be. I would also consider the starter, if it fails to disengage then the overrun will make quite the racket.

David, I’m 90% sure I had the clutch up, engaged. (not pressed) but because I wasn’t expecting to hear this noise, my attention diverted and now I’m second guessing my memory. I know for a fact that the noise stopped the moment I disengaged the clutch. (pedal down) So that’s another reason I’m pretty confident I started it with pedal up.
The Starter, which is a replacement gear driven type, not disengaging is an interesting thought but how would that relate to the noise immediately stopping when I disengaged the clutch? That’s a puzzler… I shut the engine down and started it back up and no noise, then drove it 95 miles for 1-1/2 hrs with no issues. Since it’s now heat-soaked, I’ll let it cool down overnight and see what happens from cold. This time I’ll pay more attention to engaged, or not engaged.

Are you using synthetic trans oil?

No idea. Could it make a difference? Long story short, it was a trans rebuild by a small local shop that contracted it out to a guy that was “experienced.” I’ll spare you the details. Regardless, I’ve been thinking of changing it to something known to work well like MT90 because I’ve noticed it doesn’t easily downshift into 2nd. It’s the only gear I have a bit of a struggle with from time to time. 2nd is better with a warm trans.

First motion shaft was moving, main shaft wasn’t… The small needle bearing between the two might have been a bit dry for a few seconds til the oil pump started throwing oil through the system. Pressing the clutch stopped it’s rotation. There’s a lot of weight on this small bearing as the only other way the main is held in the case is it’s rear bearing.

Foot off the clutch, in neutral, engine running, everything is turning except the main shaft and reverse gear, so there’s plenty of ways to make noise in there.

This time I was paying more attention to startup. Foot off clutch from cold this morning, no noise. Let it idle with choke on for about 30 seconds and pressed the clutch, noise started for about 3-4 seconds and went away. That rules out any starter issues. Does that sound like it could be the pilot?

Yes, because input shaft and crankshaft are turning at different speeds. Dry bushing growl.

It sure sounds like a growling bushing to me. I suppose the fix will be engine out and bushing replacement, right?

Anthony, my trans made a strange “bearing sound” when cold upon just releasing the clutch. Right at the friction point. Occured after switch to syn. gear oil. I went back to standard gear oil and the noise went away. No idea what or why. Just an fyi. Worth a try given the full remedy.

David, that’s interesting. Seeing I’m also having a 2nd gear issue, changing the oil to something that has given others good results is not going to hurt.

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How long had the car sat before you started it? Your transmission has an oil pump, but it only pumps oil when the output shaft is turning.

Excellent point, I forgot that.

The 1st time I heard the noise it sat for 1 week. Yesterday it sat overnight and it did it. Although It was much cooler here in the high 50’s F. But it only did it after I pressed the clutch pedal once (disengaged) Then it stopped. With the car stationary, I couldn’t make it repeat the noise with additional pedal presses. I put the tans in R and as I was slowly releasing the clutch, it did it at the friction point until full engagement. Pedal up down in R noise repeated as above on clutch take-up 3 times. Next, Trans in N clutch pedal down no noise. After that sequence, which lasted about a full minute, no clutch pedal movement or gear position could repeat the symptom.

David’s quote starting me thinking if it could be an issue with oil since I have no idea what I have in my trans. I know it’s has oil and it’s full because I checked it. I just don’t know what it’s full of.

Another observation that has me thinking “oil” is the noise the trans makes in N at idle. I can certainly hear it when I engage the clutch. I’m sure some noise is expected but how much is too much? On a S2 roadster with the top down, with a trans housing lined and surrounded 100% with a peel and stick thermal blanket, foam in place under the trans cover, rubber gaiter & leather boot on shifter, upholstery and the center console; with all this in place, I can definitely hear it in N at idle. But how do I determine what I’m hearing is too noisy?

Don’t overlook that it could be a crumbling or steel-onsteel throwout bearing.

Mine: It chattered and groaned at light peddle, then hissed at full peddle. Bought it that way. The former owner owned it for 40 years and at 75+ he didn’t want to deal with it.

Metal on metal:

Thanks Mitch but I only have about 700 miles on a new throwout bearing, clutch and tranny rebuild. But who knows? Maybe it’s failed or the pilot bushing is bad. Started it this morning and it was 60F, let it idle for a minute in N. Pedal down for about 15 seconds, no bearing noise. Up down again no noise. Shifted into reverse and as I engaged the clutch to back out of the garage, it growled at the friction point and stopped upon full engagement of the clutch. That was the only time I heard it today. Took it for a short 10 mile drive and no issues. I guess it’s time to start experimenting with the least expensive option first and change the tranny oil.