911SC Clutch Problem
 

Gents,
Need your help please with diagnosis and possible clutch replacement. Bought first 911 last summer-'83 SC. Have gained a good bit of experience since then. Mostly from reading this forum, Bentley manual and doing. With that knowledge I've been able to successfully change oil, spark plugs, adjust valves, etc. This is a hobby car and economics requires me to do most of the maintenance myself.

I "think" I need to do some clutch work. Probably all the stuff listed in the tech article on this forum -- clutch disc, pressure plate, flywheel, throw out bearing, etc. Symptoms: A few weeks ago the car started making a noise. It came from the engine compartment and I can best describe it as a "screaming" noise. The noise would start about 1.5 minutes after start-up and would last about 1.5 minutes and then the noise would stop. It was not coming from the alternator or AC belt. Again, it would stop on its own after a minute or so. After that, the car drove and performed well and wouldn't make the noise again until the car sat overnight and was restarted the next day (I don't drive the car every day.....once or twice a week).

Today I started the car and as expected, it made the screaming noise and as expected it stopped on its own. I drove the car about 40 miles to Fort Worth, completed an errand and headed back home on the backroads, windows open, 35-45 MPH. About half way home, I thought I heard the screaming noise faintly and intermittently. Wondering if it was the clutch, I pushed the clutch peddle in. The noise stopped. When I let the clutch back out, the noise started again. When I got within a half mile of my house, the noise changed to a softer rubbing sound. I nursed it the last half mile being very gentle with the gear changes. All the while, the car seemed to run fine.

Have I diagnosed the problem correctly? Is it the clutch? Or the throw out bearing? Or something else? As always, I will appreciate your guidance.

Respectfully,
Tom

sounds like a throw out bearing. Thing is, after removing the engine and separating the transmission, you might as well do the full meal deal (clutch, pressure plate, flywheel, throw out bearing, guide sleeve, etc. then there is the WIIT things to do, mostly cleaning and lubing, fixing leaks, upgrades. But it all can be done in a weekend as long as you have all the parts on hand ready to go. then, hopefully the squeal will be history and no need for a clutch for another 150K or several owners. try the clutch wizard in the parts section. You might also find a rubber center clutch disk!!, don't get a new one of them. the tec article on replacing a clutch is a good place to start the project.

have you stuck your head under the car while noise is apparent - can you localise it to the gearbox area??

Do not discount the alternator bearings - when these are on their way out they can scream. When you put your foot on the clutch you are removing the load on the engine and this can reflect on to the alternator load. Fixing this is a low cost and a good introductory project for people willing to get hands a bit dirty

Use a buddy or partner to localise the scream - It certainly could be the throwout bearing but as james noted its a significant job and certainly a step up in complexity from the basic maintenance you are currently comfortable with. Im in Australia and a clutch job at a shop (inclusive of throwout bearing) would cost probably 2K+

Tom, you say that your noise is not the alternator (or the alt belt, which can make this kind of noise if it's just a bit too loose). Did you remove the belt and then do the start procedure to verify?

Needless to say, this is a very strange symptom, and I find it hard to believe that you did an 80-mile round trip with no gear selection issues - with a clutch ready to have a big issue.

Thanks for your input James. I will do all the things you mention while I'm in there....while I've gone to the effort to drop the engine. WIIT (While I'm In There?). Your recommendation to use a rubber center clutch disk confused me. Everything I've read since before buying the car says that the rubber center clutch was one of the base problems with the SC along with chain tensioners and airbox pop off valve. Everything I've read says replace with spring center clutch.

Vince and Peter,
A month or so ago, I had a noise (not the scream). It sounded like what I would suspect an bad alternator bearing would sound like. I removed the belts and it stopped. A buddy of mine said he thought the alt belt was too loose and was causing the noise. We removed a shim to tighten the belt and the sound went away. I did NOT remove the belt to try and diagnose the scream however. It just didn't sound as if it was coming from the alt. It sounded as if it were coming more from the right side firewall area. I've got little to loose at this point, so tomorrow I will pull the belts, start it and see (or hear) what I've got. I just jumped to the conclusion it was the clutch today when I found that pushing the clutch pedal in silenced the noise.

Tom remove the belt and start car. Just don't leave it running for longer than the 1.5 minutes you mentioned.

On your note regarding removal of the shim - hopefully you actually changed its location and did not actually remove it. The 6 shims are always meant to be in place the only change is their location either side of the pulley half

Throwout bearing is only active with the clutch pedal depressed.

Thanks Vince. Poorly worded on my part. I've read and almost understand the reasoning to keep 6 shims at all times.

With fewer than six total shims, the nut can bottom out before the pulley is tight. The shims not only provide a means to adjust belt tension, they are also the actual spacers, along with the outer pulley half, that fill the area with no threads.

DON"T get one of them