Clutch Chatter Elimination Plan - Initial Results are Good!

[vwlover77]

OK, I'm preparing to eliminate the clutch chatter in my '78 Westy, but I'm trying to avoid spending a ton of money on all new parts. So, here is the history of the problem and my plan of attack. Your feedback and advice would be greatly appreciated!

When I bought the Bus, the clutch seemed smooth with no chatter. The first time I pulled the engine, the clutch disk seemed very thin so I replaced only the clutch disk (with a Meyle brand disk). After this, I started to notice chatter.

The next time I had the engine out, I had the shop I was working with machine the flywheel and replace the pressure plate with a new Sachs unit. The same Meyle clutch disk was reinstalled.

The chatter was still there and getting worse. So, at the next engine pull, I found the flywheel, pressure plate, and clutch disk looking like this. Notice the heat damage at 2:00 on the flywheel, and at the 12:00 position of the pressure plate. These two areas of heat damage were aligned when assembled.




AND, I found that one of the bolts for the pressure plate had failed. No surprise, this bolt was the one nearest the heat damage.


SO, I concluded that the failure of the pressure plate bolt was allowing the pressure plate surface to push out in that area and become non-parallel with the flywheel surface. I thought the heat damage on the flywheel and pressure plate and the clutch chatter was due to this uneven clamping in that location. So, I bought new pressure plate bolts, evenly sanded the surfaces of the flywheel, pressure plate, and clutch disk and put it all back together. The result: No improvement. Then I started thinking that the shop that machined the flywheel did not keep the flywheel mounting surface parallel to the clutch surface.

My plan to fix this is as follows:
1. Buy a new Sachs clutch disk. I've found a NOS one on thesamba for a decent price:

2. Use the original pressure plate. I've just finshed sanding the surface (it got rusty sitting in my garage) and the results are below. Do the photos show anything that would cause concern?






3. At this point, I do not trust any shop to properly machine my existing flywheel, so my plan is to purchase a used one in good condition, clean it up with cross-pattern sanding, and put everything back together. (Too bad I gave away a spare flywheel a while back! Doh!)
Here is the seller's photo of the flywheel that I am considering buying:


What are your thoughts on this plan? My total cost to go this route will be approximately $75.

[Bookwus]

Hiya Don,

This is just an offhand thought, but it is easy to check.............

See if the contact surface of the finger springs is parallel to the pressure plate-disc contact surface. I did this by setting the pressure plate face down on a known level surface and then used a torpedo level on the throwout bearing contact surface. Mine was slightly outtawhack and that was causing the clutch chattering in my case.

Colin had me sanding all the contact surfaces. And that, although excellent advice, would get me nowhere with parts that outtawhack.

[vwlover77]

I will certainly check it on the original pressure plate (the one in the photos). I would hope that the one I purchased new (currently in the Bus) would have had no such issues!

[Amskeptic]

Hiya Don,

This is just an offhand thought, but it is easy to check.............

See if the contact surface of the finger springs is parallel to the pressure plate-disc contact surface. I did this by setting the pressure plate face down on a known level surface and then used a torpedo level on the throwout bearing contact surface. Mine was slightly outtawhack and that was causing the clutch chattering in my case.

Colin had me sanding all the contact surfaces. And that, although excellent advice, would get me nowhere with parts that outtawhack.

Mike, unfortunately the forces acting on the diaphragm as it is cinched up to the flywheel will change any readings arrived at while unbolted. The fingers draw in and describe a small arc through their operating range at the release bearing surface. You can only draw conclusions about the fingers once the pressure plate is bolted up.

As we analyze the progression of this chattering failure and see the radical localized heat marks at the failed bolt, we have to ask exactly how these parts interact with each other. Heat suggests local friction. But you have to remember that as that local spot goes, so goes the whole ring of the pressure plate and the flywheel friction surface. A loose bolt would generate less heat at that specific spot. It cannot create more heat (as you would think if it were "slipping" there, because if it is slipping, it's all slipping.

Mill table machining (the marks as you see on the flywheel) can do a terrible job if it is not set up correctly, but how could we measure its depth accurately to see if there is run-out past allowances? You cannot measure from the stepped surface where the pressure plate edges contact.

I personally would be so gunshy of all of this that I would be doing exactly as you are with the original original pressure plate if that is the original pressure plate that you were originally talking about when you said original pressure plate originally. As to the origins of this chatter, I think replacement pressure plates are as suspect as anything these days, and utilizing the already-broken-in clutch disk with the replacement pressure plate was a possible fail point.
Colin
(p.s. these clutches work great when they work and they grate when they don't work great)

[vwlover77]

I got my "new" flywheel and clutch disk today! I hope to begin the job this weekend.

I'll post pics soon, but the flywheel has two holes drilled through it right at the outer edge of the clutch surface, and metal pins pressed into the holes that protrude from the engine side of the flywheel slightly but are well recessed from the clutch surface.

Are these some sort of balancing weights? What purpose would they serve?

[Sodbuster]

when you put it back together and you are hooking up the clutch cable, take a look at your clutch cables Bowden tube at the transaxle. This tube is more than a cable guide it requires an adjustment and it should be covered in any publishers workshop manual for air cooled VW. bug or bus the principal is the same. If the bowden tube is aligned too strait it can cause clutch chatter big time. This tube needs to have a set amount of droop or "bow" to it to act as a damper to the cable. This can be adjusted with washers over the tip of the tube where it slides into the trans clutch cable bracket, and they can go bad.



I bring this up because no matter what you did to the clutch itself the results are just the same. there may be something you missed. take a step back and look at the entire clutch mechanism from the pedal back
Just my 2 cents.

[Amskeptic]

I got my "new" flywheel and clutch disk today! I hope to begin the job this weekend.

I'll post pics soon, but the flywheel has two holes drilled through it right at the outer edge of the clutch surface, and metal pins pressed into the holes that protrude from the engine side of the flywheel slightly but are well recessed from the clutch surface.

Are these some sort of balancing weights? What purpose would they serve?

If the pins engage with holes in the pressure plate, they are locating dowels. If they just sit there, they maybe TDC sensor lugs?
Colin

[Amskeptic]

Bowden tube needs to have a set amount of droop or "bow" to it to act as a damper to the cable.

After 31 years of this, I still have never gotten such a tidy droop as in those lying illustrations.
Colin

[Sodbuster]

The droop need not be "tidy" or swank, or even elegant. the Bowden tube and it's required deflection of the clutch cable need only be presnt to assist with "Smooth clutch operation". I have seen bowden tubes installed in buses with almost zero deflection of the cable and a clutch chatter. after a simple cable (bowden tube) and clutch adjustment the chatter can be removed, if caught early and the clutch is not allowed to work under those conditions for too long.

That's 2 more cents. I'm almost up to a nickle

[vwlover77]

Thanks sodbuster! If only it had been that easy. The bowden tube has always had a nice bend, which I increased at one point with a nut (instead of a thick stack of washers). Finally I replaced it with a new one which had the right amount of bend already buillt in (after my nearly-new clutch cabe broke inside the tube) . All to no avail.

Just a few hours ago I got everything back together after replacing the flywheel, clutch disk, and pressure plate with the parts mentioned in my earlier post.

I've only driven 5 miles, but so far, it's silky-smooth and oh-so nice.

[Sodbuster]

I've only driven 5 miles, but so far, it's silky-smooth and oh-so nice.

That's the bottom line right there! Good on 'ya! Just glad to hear your sorting it out.