Educate me..When would you just replace the clutch disc?

[ben parrish]

I will be dropping the motor soon to take care of some leaks and clean it up. While I am in there I need to look at the clutch. The current unit has about 60k on it and I don't have any issues with the feel, release, etc. Can I just replace the disc? Pros and cons?
thanks,
Ben

[gtihop]

I would never do just the disk. the pressure plate wears unevenly as well. Also the flywheel wears. Do the pressure plate, disk, release bearing and either machine or replace the flywheel.The it'll be done right and won't chatter..

[JeremyD]

I just did the disk, release bearing and resurfaced the flywheel - at 56k miles my pressure plate looked great.

[mjshira]

I would agree that if you have everything apart you should replace all the parts that wear.

[911pcars]

If the PP has relatively low miles, I'd leave it in, assuming you're doing the work yourself and don't mind going back in 20k-40K miles later. For the typical owner, it's best to replace everything while you're in there. The going rate to R&R the drivetrain is what, $400?

Sherwood

[ben parrish]

I am doing the work myself so no big expense there. What do I need to look at to see if just a disc is adequate? Are there tell tell signs on the pressure plate to look for?
I put this clutch in about 50k ago due to a failed rubber center. Used the sport clutch package and have had no issues since then. I didn't even resurface the flywheel as it looked good.
I am not one to spend money on something unnecessary but don't mind fixing potential/pending problems.
thanks,
Ben

[ben parrish]

Does anyone else have a suggestion as to what to look for?

[gtihop]

check the flywheel for cracking, hot spots, grooving . have it measured for thickness and also taper. same thing for the pressure plate, but also check to make sure that the spring fingers are all sitting at the same height.
when i did mine, it was only 400. for the kit that had disk, bearing and pressure plate. it's usually cheaper to buy the kit than the individual pieces because that's normally how they are sold.

[Grady Clay]

Ben,

Good advice above.

In general, the only time when you would ONLY replace the disc is when new and oil soaked. This is usually just after a complete clutch has been replaced and the transmission input shaft seal was replaced and leaks. Some claim they can get the oil out of a new disc – I don’t think so. Sorta like un-ringing a bell. (Search on “input, shaft, dam, seal”.)

That said, if everything is OK, installing new (and clean) friction parts is generally appropriate.


The flat steel flywheel is easy to confirm proper. You can inspect it with a hand microscope (30X from Radio Shack). You can check for flatness with a straight knife edge. You can measure the thickness with a micrometer and axial run-out with a dial indicator.


The above techniques can be applied somewhat to a pressure plate but it is critical to clean one completely and do a thorough visual inspection. The large diaphragm spring can have a large crack (broken) where it is difficult to see. The condition if the fingers where the TO bearing should appear like new. Carefully inspect the housing, particularly around the guide pins.

Another often missed issue is with the pressure plate friction plate becoming off-center in the pressure plate housing. This is particularly common with aluminum housings. It is caused by extreme use of the clutch to decelerate the car after downshifting – like when you get in the wrong gear.

The three flat tension springs are put in compression and buckle. The three locating pins are forced to bend or move and can even crack the housing. This allows the friction plate to become off-center. It is easy to use the shank-end of a drill bit to check the clearance between the friction plate and the housing for concentricity. The tension springs should be flat.

Clutch pressure plates are relative complicated and not subject to as easy inspection as a flywheel. When in doubt, replacing it is the usual remedy.


There are also quite a number of features to a disc. Aside from the friction surface condition, there is the ‘compressed thickness’ of the two friction discs. This requires a pair of Vice Grip clamps with the swivel pads and plastic protectors. This is to compress the spring between the two friction discs. Use a real micrometer and check at many places around the disc. A used disc can have a piece of debris between the two friction discs and even a new one can have some manufacturing chard.

The hub of the disc assembly must be free to move when compressing the coil springs under torque load (both directions) yet be rigid enough to keep everything together straight. Checking run-out is important.

The disc must be free on the input shaft. I use valve lapping compound and lap the two splines together. After cleaning the compound off, the proper type, amount and distribution of lubricant is critical. Even a small amount of extra grease thrown off to the friction surfaces can lead to a ‘juddery’ clutch.


The sealed clutch release (TO) bearing is not normally serviceable. Most get replaced on general principal even when they appear good. The theory is that a TO bearing failure ruins the far more expensive pressure plate.


The condition, fit and lubrication of the pilot bearing is important. Always test-fit the bearing to the pilot bearing surface on the transmission input shaft.


When reusing the flywheel and pressure plate, make the friction surfaces ‘slightly scuffed’ with abrasive. You do not want mirror-like surfaces as that will cause clutch judder. The pressure plate components must have some lubrication and rust prevention but not to excess or where the centrifugal force will spin it off. The friction surfaces must be ‘lacquer thinner’ clean.



Proper clutch operation is subject to a large sequence of potential problems. Every time you have the opportunity, you should attempt perfection. That starts with the pedal and includes the pedal assembly, shaft, bushings, clevis & pin, cable, housing in the tunnel, Bowden tube & retaining strap, linkage at the transmission, shaft & bearings, TO bearing, TO bearing guide tube, fingers & pivot ring in the pressure plate assembly, etc. Even the internal splines of the disc to the external splines of the input shaft need to be perfect fit, proper lubrication and be able to ‘float’.

When you “do the clutch” properly, start with the clutch pedal pad and end with the pilot bearing, flywheel bolts and crankshaft end-play. No detail is insignificant. All it takes is a series of small issues to add up to a hard-to-detect-cause of some problem. That doesn’t mean replacing everything in sight – just pay attention to all the details in the clutch system.

Two ‘while you are there’ items are the transmission input shaft seal (and dam seal) and the flywheel seal on the crankshaft.

2˘

Best,
Grady

[Scott R]

I did a disc replace and a resurface when my wife smoked the clutch going up my driveway. The pressure plate and bearing were only a few months old however.

[ben parrish]

Grady, that wasn't 2˘worth, that was at least a dollar, man.
Good advice from all and Grady just basically sumed up everything and gave me the step by step instructions.
Again, thanks everyone.

Ben