Throw out bearing noise

[rossman]

This past weekend my son and I finally got around to installing my brand new from Nissan, z32tt gearbox in my 72 S30. It previously had a z32 (non tt) gearbox that I picked up off Ebay in used/unknown condition. It turns out that 1 > 2 and 4 > 5 synchros were pretty worn from day one, but it worked and I've lived with it until now. 

 

After installation, the throw-out bearing started making a grinding noise, for lack of a better term.  The noise was always there except when pressure is put on the clutch fork/throw-out bearing, i.e. when the clutch pedal was pressed or even with just light, direct pressure on the fork. I got under the car with the engine running and pushed on the fork with with my pinky and it stopped making noise. The bearing and collar are the exact same ones that were removed from the the z32nt gearbox that was replaced, and not making any grinding noise.

 

Comparing the bearing that's making noise to the bearing that came with the new gearbox, the noisy bearing has "teeth" on it's face and the new bearing is smooth. I believe it's these teeth that are making the noise as they lightly contact the pressure plate diaphragm tangs. 

 

I "fixed" the noise by simply adjusting the clutch pedal stop until it applied just enough pressure to engage the throw-out bearing. This seems like a band-aid solution that may cause the bearing and maybe the clutch to wear out quickly. I've put a few miles on the new setup and it seems to perform normally, and the new gearbox shifts buttery smooth.

 

Anyway, any thought on what could be causing this?

 

The other obvious solution might be to swap out the bearing with the smooth one but I was in no mood at the time to pull the gearbox again after spending a whole afternoon installing it.

 

 

[Dat73z]

Is your clutch and slave system fully bled out and the clutch fork spring bringing the ToB and collar back to rest fully disengage  the ToB from the pressure plate? Residual pressure in the system could cause the ToB to ride the pressure plate. 

 

I believe on the s30s the ToB should not be riding the pressure plate and that's how I measured it out on the clutch + ToB assemblies on my setup which is not OE (there are a couple mm of free play before ToB to pressure plate engagement) but maybe others can chime in as well. 

 

I would lean towards pulling the trans and replacing the ToB. Also ensuring all of the measurements are correct. I think you're fairly limited in what you can do with the trans in the car. I have seen clutch forks which have a hole and threaded bolt through it for adjustment but mine have always been the dimple and socket type

[rossman]

I haven't tried bleeding the system yet. It's worth a shot however the clutch feels normal and fully disengages so I doubt that's the problem.

 

I think there is always supposed to be light pressure on the bearing.

 

Here is a video of it with me pushing on the fork.

 

https://youtu.be/gYbVYxasK00

 

I'm putting ~5 lbs or so on the fork to make it stop.

[rossman]

Also, I don't know what measurements you're referring to. The tob collar is tall enough to ensure there is enough stroke in the fork to disengage the clutch.

 

I could add a longer slave push rod but all that does is push the slave piston further into it's cylinder.

[NewZed]

On 6/8/2022 at 7:44 PM, rossman said:

the noisy bearing has "teeth" on it's face

 

Do you have a picture or a link to the bearing?  Why would a manufacturer put teeth on a throwout bearing surface?  Seems odd.

 

https://www.rockauto.com/en/catalog/nissan,1994,300zx,3.0l+v6+turbocharged,1209787,transmission-manual,clutch+release+bearing,1968

 

https://www.rockauto.com/en/catalog/nissan,1976,280z,2.8l+l6,1209226,transmission-manual,clutch+release+bearing,1968

[rossman]

3 hours ago, NewZed said:

Do you have a picture or a link to the bearing?  Why would a manufacturer put teeth on a throwout bearing surface?  Seems odd.

I don't think so but I'll look to see if I have something from back when I had it out previously. It's been like 12 years since I purchased it. I normally buy bearings and such parts from Nissan or an OEM manufacturer but I don't know for sure.

 

The "teeth" are little radial ridges that are 1 to 2mm tall. It's like they are there to fit in between the pp diaphragm tangs.

 

And, like I said I had NO noises or problems previously. So, something changed and I cannot figure out what that might be.

[bunkhouse]

 I've never seen a release bearing that wasn't smooth, not that it has to be if it fits properly into the diaphragm tangs. Seems like one might hear an occasional click when pressing on the clutch pedal as the bearing meshes with the diaphragm. I'd love to hear the theory behind this supposed improvement. Just had another thought. Is it possible it's supposed to stay meshed with the diaphragm and spin all the time? Which would mean reversing your adjustment.

[rossman]

FYI, I "fixed" this issue by simply bleeding the slave and adjusting the slop out of the pedal.  I'm not sure which one actually fixed it but I've put a couple hundred miles on the car with no issues.