78 Westy Chattering 228mm Clutch

[vwlover77]

A little background:

1. Bought Bus - no chatter in clutch
2. Pulled engine, found clutch disk worn. Replaced clutch disk, reused old flywheel and pressure plate. New clutch chattered.
3. Pulled engine a second time, and found the clutch disk contacting flywheel and pressure plate only on the outer part of its diameter. Had the flywheel machined and bought a new pressure plate. Reused the clutch disk. Chatter was improved, but still there.

Here are pictures of the current state of the flywheel, pressure plate, and clutch disk. Any suggestions on what to do now???

[Amskeptic]

Any suggestions on what to do now???

Look at the heat marks remaining on your turned flywheel, at 2-3 o'clock in your photograph. Was the flywheel turned correctly, i.e. was it precisely chucked/mounted? That is peculiarly localized.

I have never had my flywheel turned and never will either. I vastly prefer to sand by hand with 180/220 grit sandpaper at a 45* cross hatch to break the clutch disk glaze. I have the original pressure plate too, hand sanded at each clutch job. Are the fingers on your new pressure plate even when it is bolted up? Is the bell housing/crankcase joining surface clean clean clean when you mate the two? Is the Bowden tube correctly sagged? Engine mounts good? Clutch disk must be absolutely dry and oil free, treat it like a record album - No Finger Prints Even.

You have to get rid of those heat marks, they are a disaster. The Pathology Report goes as follows:
When you replaced the disk with a new one, you inadvertently developed localized hot spots due to prior glaze on flywheel/pressure plate.

When you turned flywheel/new pressure plate, you inadvertently brought prior heat trauma to reconditioned/new parts via the slightly used new clutch plate with the old traumas recorded on its friction surfaces.

I will not assume that you buggered the fingers on the new pressure plate whilst installing the engine or mating the transaxle to the engine prior to actual installation.

You must sand all surfaces to get rid of old glaze, and you must be thorough and even in your sanding operation.


Colin

[vwlover77]

What about that clutch disk? From the outer edge of the rivet holes inward it looks like it has never contacted the flywheel or pressure plate, at least not while there was any slippage going on. The painted-on lettering hasn't even worn off yet!

I have carefully sanded all of the surfaces and cleaned things up nicely.

I put a dial indicator on the flywheel and rotated it by hand. Total variation in flatness across the small diameter of the face is .004" Variation across the large diameter is .006"

Bentley says .011" as a limit, so I guess I'm OK.

I was surprised to find that the heat-damaged area of the flywheel is actually the low spot, not the high spot. Can someone explain that?

[vwlover77]

I've been thinking about this... If the heat damaged area of my freshly-machined flywheel is in fact the low area per my measurements, then the wear I'm seeing on my clutch disk in the same area must be from the old pressure plate and flywheel prior to being machined, and it must have been the high area back then???

(Which I think is what Colin was trying to tell me!)

SO, should I start fresh with a new clutch disk AGAIN???

[RSorak 71Westy]

I would get a new disk, it's the chaepest part and it looks like yours is not flat....

[Amskeptic]

(Which I think is what Colin was trying to tell me!)

SO, should I start fresh with a new clutch disk AGAIN???

Yep.

Nope. Just sand it nicely and drive sensibly.

Sanding the surfaces of ther pressure plate and flywheel is not a method to re-finish the metal, it is merely a way to remove the glaze that the clutch disk is designed to put down. So sand the clutch disk with 400grit even, just to get a nice fresh non-glazed surface, and use 220 on the pressure plate and flywheel. A consistent crosshatch on the metal surfaces is important. The "low spot" on the flywheel is not really a low spot. Though the runout happens to be low there, the surface irregularity that gave rise to heat is actually a function of how the glaze from the clutch lining deposited there.

[vwlover77]

I was cleaning parts today and discovered that one of the pressure plate bolts is cracked and stretched.

I know they were properly torqued when they were installed last time, but who knows what they were subjected to previously.

Anyway, could one bolt too loose cause chattering?

[Amskeptic]

I was cleaning parts today and discovered that one of the pressure plate bolts is cracked and stretched.

I know they were properly torqued when they were installed last time, but who knows what they were subjected to previously.

Anyway, could one bolt too loose cause chattering?

Possible. . . Cracked and stretched bolt? They're supposed to be torqued to 18 ft/lbs, that is nothing. What on Earth was that thing subjected to? Was it once-upon-a-time installed with an air ratchet, I've seen it. . . . .

[vwlover77]

I wouldn't doubt it.... Here's a photo.

That's the background surface (my kitchen counter) you are seeing through the thread on the right side of the photo!

[Mr Blotto]

So sand the clutch disk with 400grit even, just to get a nice fresh non-glazed surface, and use 220 on the pressure plate and flywheel.

Umm...I think clutch disks (like brake pads/shoes) are still made with some asbestos. Dry sanding might not be the best of ideas .

[vwlover77]

Too late!

Cough, cough....