My clutch started to behave oddly after i dynoed my Z. It runs well when all the components are cold, but after 10 minutes drive, shifting becomes embarrasing. It shifts okay but it screams like a pig when changin gears. And its LOUD. I have 1 year old clutch and release bearing, could the bearing have gone bad or what?

Sounds like the throw out bearing is gone, going from your description.

Its always rotating (with exception of the series 1 which has the spring return to release the bearing) and if the bearing starts to seize it can make a lot of noise when depressed. If it gets bad enough the tight bearing will even start to spin on the clutch fingers. That can damage the pressure plate fingers as well. You shouldn't wait to long in changing it.

You can try this to determine for sure. Warm it up and raise the car so you can get under it. If you slide the clutch fork dust cover back and run the engine. Get someone to lightly press the clutch pedal you will hear is better.

Also push the clutch fork into the slave cylinder to release the bearing completly and you should hear it change in pitch (check the clutch master has enough room for the fluid). You can then play with the clutch fork pushing the bearing onto the pressure plate to hear what the bearing is doing. If its only a year old you will hear it contact the pressure plate, but its bearly noticable with the engine noise.

Chas

Edited June 9, 201410 yr by EuroDat

Just to edit Chas' post a bit...

You can try this to determine for sure. Warm it up and raise the car so you can get under it. If you slide the clutch fork dust cover back and run the engine. Get someone YOU TRUST to lightly press the clutch pedal you will hear is better.

Another voice can be heard inside the car when clutch is not depressed (that sound came after clutch change, it's not annoying but different than it used to be), slight hurrrrrrr kinda sound. Maybe its too close to pressure plate? I mean can it be? Havent really adjusted my slave cylinder rod after clutch install..

Edited June 9, 201410 yr by Reverend

The dyno will exert reverse forces on the drive train when the run is finished and the gas pedal released. Maybe that is a clue.

Another voice can be heard inside the car when clutch is not depressed (that sound came after clutch change, it's not annoying but different than it used to be), slight hurrrrrrr kinda sound. Maybe its too close to pressure plate? I mean can it be? Havent really adjusted my slave cylinder rod after clutch install..

Your model 240Z should be a series III or series IV. The throw out bearing keeps contact with the pressure plate. The slave cylinder should not need adjustment providing you have the corract pressure plate/throw out bearing collar combination. You should be able to push it 5 - 10mm back into the slave cylinder.

One thing to note: When an engine is on a dyno its no leisurley drive. The engine works hard and probably beyond what you do on a typical drive. That also goes for the drive train, but I can't see how that would effect a throw out bearing.

Another thing to note is that when you disengage the clutch, you will push the crank forward. The number 4 main journal has thrust washers to to counter act this movement. Highly unlikly, but the noise could be coming from there.

Oh and Fast Woman is right. Make sure its safe to work on. Hand brake on, Wheel chocked and someone that can follow directions and stay away from the gearstick.

Chas

Can the throw out bearing be "too dry"?

Most are sealed bearings, I believe, and pre-lubed. But who knows, you could get a dry one.

Another test that you could do is to push the slave cylinder rod in and disconnect it from the clutch fork completely. Then, with the engine running you can push the clutch fork back and forth by hand to see what effect it has on the noise. You'll be able to get it completely off of the bearing face, and also apply pressure. You'll be able to feel what's happening also through the fork.

Here's a video I found about TOB noise. I don't really like his explanation of the fix though, it doesn't make sense.

And here's a general description of a company's bearing. Pre-lubed.

Hays Throwout Bearings - Free Shipping on All Orders @ JEGS

That sounds kinda the same, except in my Z the noise comes when clutch is pressed. I shall try methods you have suggested and report back.

Can the throw out bearing be "too dry"?

The bearing are pre-lubricated with high temperature (HT) grease from the factory.

The HT grease is the difference between the Series I and the bearings after. The series I had normal grease which could stand up to 65 to 80degC. They would overheat if they had were constantly rotating.

To adjust them you simply tightened the slave push rod using two 12mm spanners and vice grips until all play is gone and then back off the nuts 1.5 to 2 turns.

I don't think you have a bearing with normal grease. I don't think anybody makes throw out bearings with normal grease anymore. If your bearing was making strange noises since install, it might be a defective bearing from the start.

Chas