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New clutch...Noise when clutch is not depressed and trans in N?


Civilizedape

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DavidF: That's the part I'm having trouble with.  If the pressure plate and release bearing are lightly loaded, the noise stops.  I am assuming "slightly" doesn't begin to release the clutch.  If I'm wrong, skip the rest ?

So the clutch disc is still coupled to the flywheel and spinning at engine rpm. 

The release bearing is now spinning at or near engine rpm. 

The torque on the transmission input shaft, if any, hasn't changed and neither has its rpm. 

The crankshaft has some axial reaction force loading it toward the front of the motor.

The clutch release lever is loaded to eliminate any free play.

I think that's everything that's going on. 

What of these, or others missed, acts on the input shaft bearing to change its loading?  Before I start assembling my car, I plan to rebuild the trans (same one as yours David F) and it'll get new bearings, but I'd really like to know if maybe something else is also contributing to the noise problem so I can fix it now.

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only thing diff between N and all the other gears engaged is the output shaft not coupled to any of the syncro hubs. So all the gears as spinning around on needle bearings, the counter shaft and input shaft are spinning on ball bearings, lots of action but for the turning of the output shaft (2 ball bearings not engaged). My guess is its just normal noise that is masked by lots of other noises that are there in any other gear. It really is a matter of degree of loudness as to whether there is a real problem or not. You can do a pretty good inspection of the gears once the case is split, and the forward counter shaft bearing (the small one) is not too hard to remove and replace if you suspect it. The main adapter plate is a LOT more involved, I would look for signs of actual failure or excessive radial play before diving into those bearings. Don't get me wrong its actually kind of fun to work on them, just saying you could end up doing a lot of work just to find out its still going to make some noise.

Edited by Dave WM
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Did you replace the throw out bearing or is it the original? Did you check if it turned freely before fitting the transmission? What you are describing sounds like a noisy throw out bearing.

If it is what I think it is, you will know soon enough when you take it for a test drive.

It will make the noise when you are driving it in all gears. If you depress the clutch pedal slightly and the noise goes away. It's the throw out bearing.

Edited by EuroDat
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1 hour ago, Dave WM said:

The main adapter plate is a LOT more involved, I would look for signs of actual failure or excessive radial play before diving into those bearings. Don't get me wrong its actually kind of fun to work on them, just saying you could end up doing a lot of work just to find out its still going to make some noise.

Thanks for the insight.  What we need is a way to test a bearing that's better than the give it a quick flick and listen test, or spin it to feel for roughness.  These techniques work fairly well after you've gotten some experience, but it's not a reliable method, especially since you can't vary the load.   As you mentioned, there are several bearings operating, and any one or more could combine to sing under certain conditions.  Of course, there's always the shotgun approach - change 'em all!

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19 hours ago, Mark Maras said:

 I always used the shotgun approach on transmissions. Along with all new bearings, all new seals, all new synchros and check the prop shaft u-joints while it's out.

What was the most commonly reported need for the rebuild(s)?

Were you ever able to do a before and after comparison?

 

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18 hours ago, Zed Head said:

Learn to enjoy the noises(s).  As soon as you remove one you'll notice another.  Coming up: diff howl, 3rd gear whine, rocker ticking, injector noise, mustache bar clunking.

Yeah, I'm with you completely.  Valve train sounds (aot noise) have always bugged me, other not so much.  A good stereo drowning out those annoyances isn't masking, it's enhancing the user experience.

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I do not understand the comments about the throw out bearing being the cause of the noise. When the clutch is out (i.e. not depressed) there is no load on the TO bearing.  When you depress the clutch, the TO bearing comes into play.  So, saying the TO bearing is making the noise in neutral makes no sense to me.  My TO bearing is brand new and noise there from day one.  Seems like transmission bearing noise to me.

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EuroDat explained it in the post below.  There's a spring inside the 280Z style slave cylinder that takes up all of the play at the clutch fork.  It can't apply much force, it's a small spring, but it is there and it does work.  If I was checking that theory out I'd crawl or reach under the car with the engine running and move the fork away from the pressure plate by hand.  You can reach it from the engine bay also.  You might have to have someone sit in the car to listen since the noise is amplified in the cabin.

Here's the FSM drawing.  I put a red dot under one of the spring coils.

image.png

 

Edited by Zed Head
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