915 5 speed serious clutch chatter

[heiltrading]

I have had this clutch out 2 times and this will be my third attempt for a smooth clutch. I first time i resurfaced the flywheel due to some light heat checking and put the disk and pressure plate back in with a new throw out bearing. The clutch worked fine however it would chatter upon release unless you got the RPMs perfect. 1000 miles later the I lost a finger from the used pressure plate and had to remove it due to rattles. During that repair i replaced the pressure plate with a new one and inspected the disk and flywheel. they both looked great. Now i am taking the clutch apart for the third time due to losing the spring clip that holds the throw out bearing. This time I am replacing everything else to make sure I get a smooth operating clutch... here are the pics

any recommendation would be great, I might be doing something wrong after 3 failed attempts.

[tobluforu]

Wow, three times, you must have this wired now. Are you getting any leaks from the rms/tranny? Is the flywheel lightened, some shave but don't balence? What you can do is get the whole unit balenced. You bring the flywheel, clutch and PP to a shop, they install it on a machine, balence it, mark it and you then install. Others will chime in that have more experience, but if a clutch disc is highly glazed, it will chatter.

[javadog]

I would replace the flywheel.

That said, I'd also check the clutch cable routing and the amount of curve in the Bowden tube.

JR

[Rodsrsr]

I never mis-match. I always do all three. New clutch, PP, and resurface flywheel. Sometimes uneven wear patterns will cause chatter.

[heiltrading]

the flywheel is original and only has 45k on it, machined once 3k miles ago now. I am about ready to get a new flywheel but dont want to spend the $400 unless im sure

[javadog]

No guarantees. I've had to replace clutches in cars I have bought with an unknown history. Some have had the flywheels machined. In some of those cases, I had some chatter. I've had no problems with clutch jobs that used new flywheels. I also use geniune parts, not aftermarket. There may or may not be a difference but I have heard of some problems with some clutch parts sourced through the aftermarket. These problems I have heard about may have nothing to do with chatter but since I haven't had a need to do any clutches recently, I've not paid attention to the details.

There are also other things that can contribute to the problem. Clutch cable/throttle cable contact, clutch cable routing, worn motor/trans mounts, etc.

JR

[911pcars]

Clutch chattering can also be caused by hard spots on the flywheel/pressure plate surface. If "resurfaced" with a regular lathe bit, the tool simply skips over the hardening hot spots. This results in an uneven friction surface.

Some suggest using a resurfacing process that instead uses a grinding wheel.

Sherwood

[NoYouRelax]

Check the runout on the flywheel. Verify that the FW has enough thickness remaining to resurface it. Check the transmission seal to see if leaking trans fluid is getting on the FW (it happened to me).

[Rodsrsr]

Originally Posted by 911pcars

Clutch chattering can also be caused by hard spots on the flywheel/pressure plate surface. If "resurfaced" with a regular lathe bit, the tool simply skips over the hardening hot spots. This results in an uneven friction surface.

Some suggest using a resurfacing process that instead uses a grinding wheel.

Sherwood

When I rebuilt my 915 I took it to DeJung Motorsports and I remember him telling me that he had to send the flywheel to a machine shop that specifically does Porsche work. he mentioned that the resurfacing process was different so maybe this is what he was referring to?

[911pcars]

Originally Posted by Rodsrsr

When I rebuilt my 915 I took it to DeJung Motorsports and I remember him telling me that he had to send the flywheel to a machine shop that specifically does Porsche work. he mentioned that the resurfacing process was different so maybe this is what he was referring to?

Grinding a flywheel isn't a Porsche-specific process.

Maybe the fact some Porsche flywheels require two surfaces to be reground equally (e.g. early 911). If only one surface is cut or both cut unequally, this will upset the preload pressure on the clutch disk.

Sherwood

[manbridge 74]

I'm in the new flywheel camp.

That said, if it's a question of the last 915 flywheel on earth I'd consider putting shims between the crank end and flywheel to make up the amount removed due to machining. Also checking runout both before and after...

[lrodri64]

Hi,
You need to install some washers between the clutch cable cover and the place where it enter in the trans. to increase the bow. Someone mentioned before.

I have fixed some vw,s and some porsche,s doing that.

[SCadaddle]

A washer, used as a spacer on one of the lower engine studs while it was on the engine stand, IF left in place when you bolt up the engine to the transmission WILL cause clutch chatter. Been there, done that.

[kodioneill]

Transmission and engine mounts can cause chattering if worn.

[heiltrading]

Originally Posted by SCadaddle

A washer, used as a spacer on one of the lower engine studs while it was on the engine stand, IF left in place when you bolt up the engine to the transmission WILL cause clutch chatter. Been there, done that.

Assuming your bell housing had a gap on the bottom? This should be obvious when under the car?

[heiltrading]

I placed a dial caliper on the outer edge where the 225mm friction disk would ride and then turned the engine over slowly to check run out. I didnt have anything over .008" however this could of been due to some crankshaft movement....Either the case I thought .008" was good?!

[javadog]

Originally Posted by heiltrading

Either the case I thought .008" was good?!

That's double the maximum runout published in the spec book. I recall it being 0.1mm, or .004".

JR

[heiltrading]

I think my process had a flaw then lol, there is no way the crankshaft could hold .004" spec during a 360 degree rotation.

[heiltrading]

ill take off and have a shop determine the run out....that should confirm if the flywheel is junk I hope.

[javadog]

The measurement is the runout on the perimeter of the flywheel. I don't know that Porsche intended it to be measure while installed on the engine.

JR