1996 OEM Clutch Pressure Plate Issue / Spec Question

[ftuhy]

Per page 12-11 of the manual, Pressure Plate Inspection, the clearance between the pressure plate frame and the plate should be .001" new, .006" at the service limit. Mine measures .060" - 10 times the service limit.
Is the manual spec correct? (With further thought, is that spec the difference between measuring at 3 points? If so, is there a spec on the absolute value? Wording in the manual is not precise.)

My issue: clutch engagement point kept getting higher and higher until it was less than 1" from the top. After a drive of an hour or so, when passing through the engagement point, the clutch would make a sound like rivets were chewing into the pressure plate or flywheel. However, no slippage in any gear & shifting OK at high RPMs.

I pulled the trans & clutch, and was quite confused (and still am). With 50kmi on the OEM assembly, everything looked good. Disc thicknesses and rivet depths were very close to the Standard (New) spec.
Hydraulics are fine; no leaks, fluid level hasn't changed in 20 months, slave piston travel observed as more than one inch. No burn marks on the pressure plate, intermediate plate, or flywheel. Throwout and pilot bearings very, very smooth and quiet.

Then, I measured this pressure plate clearance and it appears to be way out of spec.

If this is the problem, then I simply (expensively?) buy a new clutch assembly. But, I've never heard of a pressure plate fail like this. Anyone else ever encounter this?

 

[JD Cross]

No one else has posted so I'll plow ahead.
Page 12-11 is the procedure to check for pressure plate warpage.
Three measurements are done to check warpage around the plate to compare to the service limit of 6 thou.
The straight edge doesn't touch the frame just the smooth surface of the plate.
The feeler gauge will tell you how much warpage you have.

Did you place the straight edge on the frame and measure the distance to the plate?

 

[ftuhy]

Thanks. I think I was too tired when I did this. Indeed the straight-edge was touching the frame.
So, I just did it the right way. I can barely fit the .001" gage, and that's due to wear on the disc area vs the untouched outer rim of the surface.

Back to figuring out what's wrong with the clutch when everything appears to be in spec and hardly worn. The (hydraulic) clutch damper is back to being a suspect.

 

[JD Cross]

Good news.
Sounds like your existing clutch is within the service limits.

I know bearings that are failing can make quite a racket but you've checked for smooth turning and excessive play so that would seem to be out as a noise source.
There are other smalls bits in the clutch that could be loose/rattling but that's the beyond my clutch knowledge so perhaps others will chime in.

Wondering if you've got leakage past your master and/or slave cylinder piston seals or perhaps a bad bleed with some air pockets.
You wouldn't have any system leakage so fluid levels would stay full but you'd be losing release bearing travel.
Any scoring on the cylinder walls?

Have you also tried adjusting the pedal free play?

 

[davidf]

I can't imagine it being a hydraulics issue since you have mechanical noises coming from the clutch area. The pedal height getting higher is weird too. Do you have any freeplay at all?

 

[ftuhy]

I have about 1/2" of total pedal free play, which matches the manual (.35" - .59"). Clutch hydraulics were flushed last September, 3kmi ago (just before the drive to NSXPO and play time on the skid pad there), and fluid level in the master hasn't budged.

The 4 damping springs in each clutch disc look good, feel tight.

I'm now wondering if the "screech", which occurred only just at the start of engagement when the car had been driven a few hours in hot weather, was the surface of the bearing collar just starting to touch the clutch fingers. It would also make that noise in the past when first starting out in very cold weather.
Possible explanation: Those are two steel surfaces engaging with no lubrication. Once there's enough pressure applied for the bearing to be hard up against the fingers, the bearing collar spins and all noise goes away. I may try putting a very, very, very thin film of the high temp urea grease on that surface of the collar.

I've driven the car for 14 years & nearly 50kmi. Yet the disengagement/ engagement point seems to feel higher than usual. Couldn't be a failing memory! Hmm Perhaps an outside influence, but is it too little or too much wine?

On the hydraulics, my thought was that maybe the clutch damper is not fully releasing the pressure to the slave, making the release point higher. On further thought, if it did that, shifting at 7k - 8k rpm would be affected, and that was fine.

Anyway, my intent was to do the CV refurbishment as part of this job (the boots have started to ooze grease), so only about 40% of this work was wasted.

 

[JD Cross]

Frank
I've had my NSX for 23 years and never had a sound from the clutch.
If I did have screeching sound I'd be looking at bearings first.
While you've got the clutch out why not replace the pilot and release bearings just to be sure?

 

[davidf]

On the upside, with 50,000 miles on your clutch and your specs are near standard is excellent news. Not many can say that at 50,000 miles.:wink: