Nol, 95 993 C4

I was driving in town in 2nd and 3rd gears 4-3000 rpm when I heard a loud clunk coming from the pedal box. I was changing down to 2nd at that moment and the force required to press the clutch increased by a factor 3 or thereabouts instantly. Ihave driven the car like this for a bit and it works fine, just that the clutch feels like a heavy duty competition item.

What could cause this?

I searched the archives but could only find posts on clutches going gradually, not instantly.

The prelim dealer diagnosis is that my cluch needs replacing. They'll check in more detail after the weekend (which is Thurs-Friday out here) but the pedal box was opened and nothing untoward could be detected there. Ihad a look in also and it looked very clean, no loose bits no leaks no split covers.

the car is a '95 C4 @120k km. It has a history of "clutch pedal not fully returning". 2 years and 15.000 km ago the slave cylinder was replaced.
However, contrary to many posts here, this did not cure the pedal problem. Subsequently the P-dealer mechanic upgraded the the pedal return spring for a stronger one but still the pedal return problem persisted. It also has the typical squeak noise. Last year, after chasing this for 18 month or so with no ill effects on daily driving I gave in and lived with it. But now this , TIA for any feedback.

Enjoy

Nol

Ron

Check the p-car.com DIY section for the clutch kinematic lever update. That sounds like what you need.

That part is about USD $60.

Robin 993DX

Nol,

It is possible the spring assist in the pedal assembly became defective. Possible cause (spring poped loose, lever broken etc...) The first place I would examine would be the pedal cluster area.

Like Ron mentioned, check the clutch kinematic DIY for detail information on the pedal assembly.

The clutch pedal mechanism works by a two part power assist. When you first push down the pedal the pressure you feel is from the spring tension built into the pedal cluster assembly, a little before half way point you enter the 2nd half of the travel and the pressure you feel is from the pressure plate but asisted by the spring tension of the clutch pedal cluster going in reverse to help push the pedal down. Since the clutch pressure plate have so much pressure, it over comes the pedal cluster spring tension and requires you to apply more pressure in order for the clutch pedal to travel down.

The function of this complex mechanism is self evident when you disconnect the hydraulic pressure line from the clutch pedal cluster. What's most amazing is that once it is adjusted properly (with the small allen adjustment screw to determine the stop of the spring) the transition is completely undetectable.

Nol, 95 993 C4

Ron, Robin, Thanks for the help.

So you reckon I should concentrate on the pedalbox. And the increased pressure to operate the clutch is simply the full force of the clutch pressure plate without spring assistance from the "power spring" (that's what the P-car parts computer calls it).

I certainly wouldn't mind if that turns out to be it. I'm still trying to work out what failure of the parts in the slavecylinder - pressureplate - forks - throwoutbearing assembly could cause the symptoms.

Enjoy

Nol

Robin 993DX

Nol,

Of course that's just a guess on my part from a "blind" diagnostic.

Nol, 95 993 C4

Robin,

One idea for this thread is to see if I get a couple of replies in the "same happened to me and it was..abc" category. Not So far.

Your "blind diagnose" is likely to be more to the point than me actually sticking my head in the footwell. If only i'd posted the query before, I now have an idea what to look for. If it wasn't for your explanation above I'd never know that the spring has a dual mode. I did press the clutch and watched the spring was not broken or out of place. It seems now there is more to it that warrants further investigation of the clutch pedal assy.

In your opinion what would happen if the adjustment screw for the stop of the spring backed all the way out?

Thanks Nol

Edit: I just revisted P-car.com's DIY pages and seeing the pictures it struck me: I didn't see the split cover for the master cylinder because there wasn't a cover on it.

Robin 993DX

Nol,

It is difficult to based my answer on memory, but I think if the adjustment screw is all the way out than the clutch pedal would be hard to press down.

The factory shop manual recommends a specific adjustment range mesaured in mm, sorry I don't have that information with me.

JC in NY

Definately sounds like the spring assist and probably nothing to do with the clutch internals. Incidently, Cup cars omit this assist spring entirely giving a more sensitive pedal feel at the expense of greater force required.

Nol, 95 993 C4

Thanks for chiming in JC. The clutch action does remind me of a heavily tuned 993 I have driven earlier this year. The Gemballa modified machine has big turbo power, a GT2 gearbox and a competition clutch, made my 993 feel like a comfy pair of slippers after swapping back. But I digress.....

Enjoy

Nol

Nol, 95 993 C4

Update after inspection: no evidence of any problems in the pedalbox. Adjustment screw is all far enough in, and the spring engages correctly.

Currently assuming the clutch is worn at 120,000 km. A very crude test involving the handbrake and engaging 4th gear shows slippage. The suddenly heavy clutch would have to be caused by the pressure plate then? I'm still a bit puzzled but we're moving ahead with the clutch.

Thanks, Nol