CatoBT

Hello,

Lately my '78 has been acting strange:

When putting in 1.st or reverse the whole car is shaking wildly before I engange the gear completely. After driving for a while (10 mins or more) the sympthoms seem to disappear (when I return home and backs into the garage, there is little or no shaking).

I had a talk with customer service at the local Porsche dealer in Oslo, and they said it could be som oil-leak onto the pressure plates.

Does anybody know anything about this..?

There is absolutely no problem shifting up/down between other gears.

Brgds

Cato

Dave928S

It's unlikely to be oil, as the only possible leak near the clutch is from the rear main seal, or sump, in front of the flywheel ... and it's difficult for oil to get from there to the plates.

It could be that plates are at the limit of wear and you are getting shuddering when cold, which is not an uncommon symptom with worn driven plates. How may km's has the car done?

It could also be a hydraulic issue which might respond to bleeding. Have you noticed any leaks on the garage floor?

Dave928S

Additional oil entry point is from the top where the release arm ball cup is. It would be possible for oil to drop down from there ... but there would have to be a fairly serious leak, and you'd be generating a smoke screen from oil dropping on the exhaust also.

CatoBT

Dave:

Thanks for very fast reply!

There are no major leaks as far as I can tell. Some oil is dripping from the drain plug (not very serious/need to thange it I guess). No smoke noticed.

The car has approx 300000 km on it (the previous owner claimed to have changed the clutch but I don't know if he really did it...).

I guess a change of the cluch could be needed (I guess this is a major/expensive repair? ).

Cato

Dave928S

As you have no significant oil leaks I think you can regard oil on the plates as unlikely.

If the clutch hasn't been done, then 300,000km would mean that it's highly likely to be worn out. Maybe the PO did a half ***ed job and replaced only some parts.

What would likely to be needed at that mileage would be:
1. new crank end pilot bearing.
2. new pressure plate.
3. new release bearing.
4. new driven plates.
5. reface flywheel.
6. clean up intermediate plate and ensure it can be reliably adjusted (expensive to replace)
7. check stub splined shaft has no ridges and replace if necessary.
8. replace ball cup on release lever.
9. check/refurbish clutch slave cylinder.

The clutch pack on a 928 is quite easy to remove and replace, as you don't have to remove major components like a gearbox. You can count on spending about $1200 US in parts (a vendor might verify current costs ... Roger?) ... more if your intermediate plate or stub shaft need replacement.

The bottom line is that you'll need to have a look at the clutch pack, release arm and slave cylinder to see what's going on, as the first step.

It's not a difficult job with help from here the first time you do it.

Lizard928

Check to ensure that all of your bellhousing to engine bolts are properly torqued down.
If they are slightly loose, you will get these symptoms.

Dave928S

That's a good thought ... maybe the PO loosened them for some reason (to get additional clearance to get the clutch pack out?) and didn't torque the bolts back up.

Checking the bellhousing to torque tube bolts and pinch bolts would also be worthwhile, while you're checking the clutch pack, release arm, and slave.

Although ... with any loose bolts you'd expect the symptoms would be more likely to be present hot or cold, and not just cold.

It'll be interesting to hear what you find ... and post some pics if you can.

Lizard928

Dave,

As metal gets hot (especially Aluminium), it expands closing these gaps and increasing tension.......

Dave928S

Aaah ... yes ... hadn't taken that in to consideration (coefficient of expansion is about 2 to 1)

With all the aluminium components a 928 is a moving target as far as operational clearances/stresses are concerned.

I think I'll go and get myself a bourbon and have a think about how/if that might influence clutch operation ... maybe I'll have two.