How in the World could this happen??

Flatsixhead · Flatsixhead's Garage

My clutch failed in March and I had a new torque tube and all clutch components installed. 300 miles later the "clutch blew up" according to my mechanic. The car has only been driven by me with respect and not tracked or raced. How in the world could this happen?? My mechanic said that the clutch disk failed twice and he has never seen this happen to anyone..

flash968 · 08-28-2009, 03:08 PM

i've seen new clutches go with people who rest their foot on the clutch pedal at stops, and with people who use the clutch to slow down (slipping the clutch to slow down rather than getting off of it and letting the engine spin down off throttle)

i've also seen new clutch disks go if the pressure plate was reused without surfacing, and the same with the flywheel

i've also seen them go if there was a rear main seal leak

any of those going on?

Techno Duck · Techno Duck's Garage

Need more info about the 'blow up'. What actually failed? Friction material, throw out bearing, spring center..?

mikepellegrini · mikepellegrini's Garage

Quote:

Originally Posted by flash968

i've seen new clutches go with people who rest their foot on the clutch pedal at stops, and with people who use the clutch to slow down (slipping the clutch to slow down rather than getting off of it and letting the engine spin down off throttle)

If you match RPM's when you downshift to use engine braking, it's less hard on the clutch than when you start from a stop.

But you gotta match RPM's.

flash968 · 08-28-2009, 06:42 PM

absolutely - many people do not do this though - it is not a technique taught off the track, and not an easy one for some to learn - my wife still can't get the hang of it, and consequently refuses to drive the 968 with the aluminum flywheel, which requires every shift be gear matched

onZedge · 08-28-2009, 06:51 PM

(Sorry, I couldn't resist)

I use the clutch to hold me from rolling backward when I'm on a hill at a light. Stepping on the brake pedal is such a bother. Is that bad for the clutch?? I mean it makes the disk thinner and lighter so it adds more horsepower. Right??

'scuse me, I just got a text...

TibetanT · TibetanT's Garage

Flatsix:

Ouch!

What type of clutch disk are we talking about here?

Sachs, Centerforce, another brand?

I am really getting at quality of parts and of course workmanship too. It would really surprise me to hear that a new Sach clutch kit blew out twice.

Getting ready to do a client's car, so that's why I am asking.

TibetanT · TibetanT's Garage

Flash:

Doesn't main seal leaks cause slipping more than failure?

Of course, now that I am mentioning it, oil all over the internals of the clutch and pressure plate still means removing everything to remedy the problem.

Techno Duck · Techno Duck's Garage

I've heard the RMS thing many times but can't honestly see it causing clutch problems unless it's sparying out. Reasoning is the flywheel is completley separating the clutch from the RMS. I could see the oil being slung around by the flywheel, but again you would need a pretty serious leak for that.

Another possibility is a leaking heater control valve, unfortunatley that will take a dump right onto the bell housing.

Porsche-O-Phile · Porsche-O-Phile's Garage

Do NOT use the clutch to hold yourself from rolling at a hill. This is poor technique. Use the brake until you're ready to actually start moving the car forward. While on an incline, I typically will hold the brake with the gear selector in neutral. When ready to start actually moving, I pull the e-brake on and release the pedal brake. As I do so, put the clutch in and shift into first, and start letting the clutch out to "grab" as the e-brake is released. Practice it a few times - you shouldn't roll backwards an inch. Even on a really steep grade, you have the freedom of your right foot to add throttle and give it a little gas as you release the e-brake and clutch - either way, you shouldn't roll back an inch and your wear/tear on the clutch is minimized.

NEVER use the clutch to hold you on a hill indefinitely. This is a surefire way to burn up clutches quickly.

Edit: I think the comment above was tongue-in-cheek, but I just had to say it in case...

Flatsixhead · Flatsixhead's Garage

Sachs CUP clutch kit with pressure plate, new T/O bearing, fork, etc etc etc.. I told my mechanic to replace everything because I did not want to go back in for a long time.. Need to ask him if the fly wheel was resurfaced. He told me yesterday that he believed that the disk failed near the center and showed very little wear on the surface. I have not been able to drive the car all summer long and as I had the transaxle rebuilt as well. I'm losing my mind!!

Flatsixhead · Flatsixhead's Garage

How long should a clutch last if you treat it nice?

flash968 · 08-29-2009, 01:27 PM

yeah - using the clutch to hold a hill just fries those things - won't take long either

if fluid gets on the friction material, it softens it and will cause it to fail early - you should see signs of such a leak if it's there

failure to have a smooth clean surface on either the pressure plate or the flywheel can cause hot spots on the disk and cause it to fail

Gary2397 · 08-29-2009, 10:28 PM

How long should a clutch last? It depends on the driver. The simple
answer is up to 10 years or more. I had OEM Sachs on my 83 944
10 years now. My car is driven daily.

flash968 · 08-30-2009, 05:14 AM

depends on the application, car condition, yada yada - there are a lot of factors, some listed above

with a lightweight flywheel and track duty, it can be as little as 25k (that's what i got out of my last one), but usually a bit more

stock, roughly 75k-90k is "average" - some need it sooner - some need it later

dual mass flywheels are generally easier on clutches that single mass ones

lighter pressure plates are easier on disks than stiffer ones

freeway driving is obviously easier than city driving

you get the idea

earlr85944 · 08-30-2009, 06:15 AM

i have seen early clutch failure when the free play was incorrectly adjusted
new clutch lasted @ 4 months

onZedge · 08-30-2009, 06:35 AM

Quote:

Originally Posted by Porsche-O-Phile

...Edit: I think the comment above was tongue-in-cheek, but I just had to say it in case...

Thanks. I was beginning to wonder if everybody had their sarcasm radar turned off.

Regarding the premature clutch failure: Was the mechanic that did the clutch job originally, the same mechanic who is diagnosing this failure?? This is an unusual failure and the mechanic may be shifting blame to cover up an "installation malfunction". Unfortunately, you may never know if that was the case. It is difficult to find good Porsche mechanics and when you do, they may not want to work on your car because it is "too old".

Regarding toe-heeling: Two ways to do this during downshifts. One is to literally use the ball of your foot to brake whilst blipping the gas with the heel of your foot. I feel this method is awkward. The other way is to use the ball of your foot to brake while using the edge of your foot (the part your little toe is connected to) to blip the gas pedal. I feel this method is more natural and easier to master - it also helps if the brake and gas pedals are close to the same distance from the floorboard.

HondaDustR · 08:28 AM

Quote:

Originally Posted by onZedge

Regarding toe-heeling: Two ways to do this during downshifts. One is to literally use the ball of your foot to brake whilst blipping the gas with the heel of your foot. I feel this method is awkward. The other way is to use the ball of your foot to brake while using the edge of your foot (the part your little toe is connected to) to blip the gas pedal. I feel this method is more natural and easier to master - it also helps if the brake and gas pedals are close to the same distance from the floorboard.

Especially if you have big feet and long legs, the second way is so much easier. I like double clutching downshifts myself, since spinning up both the driveshaft and the pressure plate is alot to ask for from the syncros, especially if the rpm spread is large between the two gears. I know it's old school and all, but I don't want to have to do syncros anytime soon...and I hate it when the 2nd gear syncro starts getting bad, but I would never know anyway.

Personally, I hate it when people don't rev match their shifts. It's just lazy and shows you don't know your car very well. You could almost make a clutch last forever if you were good at it, and I would think you would need to do it on something with a super harsh racing clutch.

dmilzoff · 08-30-2009, 12:29 PM

I had a clutch fail in an older Camaro which I bought new. It failed at 400 miles. They tried to blame me, but I know how to use a clutch. They finally agreed to fix it under new car warranty. The second clutch lasted 90,000 miles before I sold the car.

Slam · 08-31-2009, 10:18 AM

Did the shop replace the flywheel bolts?

When I bought my 83 944 I had to have a clutch put in. That was back in 1994. I measured the clutch a couple of months ago just out of curiosity and I've got 1/3 left on it. That's in a daily driver.

That said, I just did the clutch in my 924 and it was in great shape but had failed in the centre. It happens. This clutch was bad when I got the car, so who knows what happened to it, but it actually looked pretty good for a failed clutch. Odd.