901 clutch mystery

jkess · 09-17-2006, 05:16 PM

What I thought was going to be a simple clutch replacement job has now turned into a real mystery.

I have a 1971 911T that has had a ’69 901 transmission with push type clutch in it ever since I have owned the car (15 years). During my last track event my clutch had a malfunction that ended my weekend. Looks like another project for the shade tree mechanic. When I pulled the engine and removed the clutch I found a disc that had become unriveted. No problem, just reorder another clutch disc and I am back in business. Here is where it gets tricky. When I reordered the disc, the part number that I had used for my previous clutch job (901 116 017 01) was no longer available. Was told that disc 901 116 014 00 should work fine. It was ordered, I installed it, everything looked great except for one problem – the clutch would not release. I tried adjusting it but with no success, I could not get the car in gear. After taking the engine out again and checking everything to make sure that I did not do anything stupid, I still ended up with the same result – a car that would not go into gear.

I decided to take it to my local mechanic to see if he could solve the mystery. He checked my work, reinstalled everything and had no better results. We decided to reorder another disc (same part number), a new pressure plate (901 116 003 01) and a new pilot bearing. The flywheel measurements were checked and were well within the necessary specifications. The new parts were installed and guess what – still the same results.

Something tells me that the discontinued disc may be the answer to my problems. We called numerous sources and everyone said that the pressure plate and disc that we have ordered should work. My mechanic has suggested that we try another 901 transmission. My transmission is fine and I just need to find the correct disc, pressure plate combination.

Can anyone offer any suggestion on how to solve this clutch dilemma? I am dying to get back on the track, the engine is ready for action. I just need to find a clutch that will work. If I do need to go with the new 901 transmission, should I stick with the push type 901 or switch over to the pull?
Thanks

84toy · 09-17-2006, 09:12 PM

A couple of questions...

1. Did you compare the thickness to the old disk (if available)
2. Does the throw out arm move enough and not another problem somewhere else like a cable or tube? Watch it while someone steps on the clutch pedal
3. Is the step on the flywheel the correct dimension?

Plavan · Plavan's Garage

My guess is that you have an 911S Aluminum Pressure plate. They only made these in 1969 for the 911S cars only. They had a very special thinner clutch disk. All flywheels are the same, but the rare aluminum pressure plate is the kicker.
I had to have 1mm machined off my aluminum pressure plate (you have to take it apart) then have a 8mm custom clutch disc made because I could not find any of the clutch disc's.

If you can take a picture of your pressure plate/ or weigh it you will have the answer really quickly.

jkess · 09-18-2006, 04:30 PM

I did not measure the thickness of the disc that was bad. Because it was completely separated I trashed it. I have had the flywheel step measured and it is within tolerance. The throw out arm is moving plenty(approx. 1 ") to release the clutch you would think.
As far as the pressure plate being a 69S, I do not think that is the case. It weighs 10lbs pretty heavy, and I have also ordered and installed a new pp that is supposed to work with the new disc that I have ordered. Where did you get a custom disc? That may be an option????
thanks

Plavan · Plavan's Garage

I think the clutch shop is named "Clutch Masters" in Fullerton, Ca. I can try and get the number if you really need it. It sounds like you have all the parts coming though.

Zeke · 09-18-2006, 05:08 PM

Is there a washer under the ball pivot? You might need to remove it. Better check this theory out further before jumping to conclusions. It's some old 914 knowledge I have. Also uses a 901 "push" clutch. If one were to face the flywheel for lightness or reconditioning, the amount lost had to be added to the ball pivot to compensate and have the release arm between the tolerance points. I don't know all what you have, was done, whatever. Just letting you know that a thicker disc might have the same effect as putting that flywheel surface back in. So, maybe you need to remove a washer. If none there, I don't have a clue unless it would be to put one there. Right now at this point, that's counterintuitive to me.

Zeke · 09-21-2006, 12:58 PM

Whatever happened here?

jkess · 09-22-2006, 05:30 PM

I have tried it with and without the washer. Same results, an clutch that will no release.
My next step now is to try a new CenterForce clutch package. I have been told that trying to match up discs and pressure plates for the early push 901 transmissions is not an easy thing to do. Kind of hard to believe but I have exhausted all of the possibilities with the original Porsche part numbers that are left for this clutch. Apparently CenterForce has seen a need for this item, I hope this is the answer !!!!
I should be getting the new disc and pressure plate in on Monday or Tuesday. I will let you know the outcome.
thanks

84toy · 09-22-2006, 06:06 PM

One thing is for sure. If the disk is a different thickness, the fingers on the pressure plate will be effected. When everything is bolted up, what do the fingers look like? Are they straight? Aiming in? Aiming out?

jkess · 09-24-2006, 04:11 PM

Fingers are straight when bolted up.

Grady Clay · 09-24-2006, 05:36 PM

jkess,

Your original 901.116.017.00 is the thin ’69 911S only disc. If you have a 10# pressure plate some PO probably machined the flywheel pressure plate mating surface to work with the thin disc.

Now that you have the standard 901.116.011.00 disc the normal pressure plate (901.116.001.00) is too close to the flywheel friction surface. In this configuration I suspect the fingers hit the hub of the disc before releasing the disc friction surface. It is even possible that the fingers are interfering with the springs in the disc hub making it seem like the clutch isn’t releasing.

How to test.

Find another 215 mm flywheel. Even a 914-4 will do. Install your new disc and old pressure plate and note (measure) the finger position. Install your new disc and new pressure plate and note the position. Repeat with your flywheel. The fingers should be farther in toward the disc hub. If not, check for interference between the fingers and the disc hub. This should clear up the mystery.

How to fix.

An easy fix is to space the pressure plate away from the flywheel mounting surface. You can use ground flat washers under each of the nine bolts. You should add six 4 mm roll pins to index the pressure plate to the flywheel. This will allow you to use the new disc with your old pressure plate or the new pressure plate.

You can also have a custom disc made just like the thin ’69 911S disc that was in place all these years.

Best,
Grady

racing97 · 09-25-2006, 01:55 PM

Quote:

Originally posted by Plavan
I think the clutch shop is named "Clutch Masters" in Fullerton, Ca. I can try and get the number if you really need it. It sounds like you have all the parts coming though.

Clutch Specialties is in Fullerton on State College
Clutch Masters is in Rialto

84toy · 09-25-2006, 02:44 PM

And if it comes down to it, I have a 69 911S flywheel here....

Plavan · Plavan's Garage

Quote:

Originally posted by 84toy
And if it comes down to it, I have a 69 911S flywheel here....

All 215mm flywheels are the same (except the rare race ones), On the 69 911S it is only the clutch disc and aluminum pressure plate that are different from the other models.

So any standard flywheel from a 911 T, E or S (or 914) will work for him.