When should clutch be replaced

[andreic]

These days I am finishing a rebuild on a 1.8L engine for my 1975 914.

Some questions I am trying to decide about. The clutch in the old engine (still in the car) seems fine to me. (That engine has 95k miles, but I don't know when the clutch was replaced.) How do I decide whether to replace the clutch or not? If I do replace it with a Sachs unit, can I just replace the disk, and keep the throwout bearing and pressure plate from my current clutch, or do I need to replace all three?

Finally, how do I decide if my flywheel needs resurfacing?

Thanks,
Andrei.

[andreic]

Bump -- anyone can help with this issue?

[Steam Driver]

There is really no set time for clutch replacement. It depends on vehicle usage, driver skill and habits, etc. I can generally get 70K miles out of a Porsche clutch, even with autocrossing, etc. My '91 Honda CRX Si went to about 220K with no issues. It depends on how much you slip it engaging, do you (or anyone else or in the past) "ride the clutch" (with their foot) while driving, etc.

If the clutch is slipping or you can smell it, then for sure something needs to happen. (They can get pretty bad and still work more or less. I remember a '66 911 that by the time the clutch was being installed it wouldn't pull the front wheel over a downspout splash block that it hooked backing into the garage.)

When you get it disassembled you can inspect the disc, but at that mileage it should be replaced as a matter of course. Too much labor involved getting to it not to replace it "when you're in there" and the cost is relatively minor. Do not use a rubber center disc (if those are still available) as it came from the factory. Spring center only.

Inspect the surfaces of both the flywheel and the pressure plate for heat checking. Discoloration is OK but no roughness, etc. The flywheel can generally be resurfaced (unless it's been done before, but your machine shop can check all that) but not so the pressure plate.

If I was in there I would do it all; disc, pressure plate, and throw-out bearing. Again, because the labor to R&R the components so much a part of it. You might be able to get by with reusing the pressure plate, but again at that mileage (and just age) it could be taking a chance. Whatever you do, DO replace the throw-out bearing. I did a 356C clutch once where I knew the T.O. bearing was relatively new (I was redoing a previous clutch job where the mechanic used a VW transporter clutch disc that wouldn't reliably disengage for some reason or other.) so I reused that "new" T.O. bearing. Big mistake. It got noisy in a short time (which I ignored unfortunately) and ended up destroying the pressure plate.

So, lesson learned. T.O. bearings are cheap; do not reuse or at that mileage anything else but the flywheel) unless you just enjoy pulling and splitting the power train!

[Dave at Pelican Parts]

Since it's easier to drop the trans on a 914 than just about any other car I can think of, it's not the worst idea in the world to re-use clutch parts if they look good. (N.B--I'm never doing a FWD clutch again! Ever!!) But you have to realize that you are taking the risk that some part might be worn out.

A flywheel needs re-surfacing much like a brake rotor: If there are ridges or flaws you can catch your fingernail in. Or if the metal of the friction surface is blued (with heat) or soft. Note that the friction surface, and the mounting surface for the pressure plate (up around the edge) and the center surface that the bolts go through to mount the flywheel should all be machined the same amount. You want to preserve the relationship between them. And you may need to add a washer under the pivot for the throwout arm, but you will have to resort to try-and-check for that.

--DD

[andreic]

Thanks for the replies. So if I decide to replace just the clutch disk, and not the flywheel/pressure plate/throwout bearing, can I use a Sachs clutch disk instead of the original one, and keep all the other parts? Or is there some incompatibility between them?

Thanks, A.

[Dave at Pelican Parts]

No compatibility problems that I am aware of. The friction surfaces of the flywheel and pressure plate should be the same either way.

--DD

[porsche930dude]

It only needs replacing if it slips or makes noise. A good kit usually contains everything except the flywheel. And all that stuff should be replaced. pressure plate springs get worn. its a diaphram shaped spring. that cant last forever. plus they wear where the throwout bearing rides. All that effects tolerances and clamping force. Definatly do the throwout bearing and pilot bushing. If the flywheel looks not too bad you can usually get away with just roughing it up with a roloc disc or similar. but it should be checked for flatness not just scoring. Resurfacing is pretty cheap if any doubt. usually 40-80$ small clutches like ours can even be done on a brake lathe. but take them the flywheels specs because some techs wont care to check. Also make sure the throwout fork stud is tight and the bushing in good shape. I put a light coat of anti-seize on the splined shaft so the clutch dont get stuck from the car sitting around for extended periods

[Jrboulder]

Any shop manual should have details on how to evaluate your clutch. Basically you measure the thickness of the disc, look for glazing or burning on the pressure plate and flywheel and feel the TO bearing under load to see if it makes noise or feels rough.