'70 clutch still broken, help needed to make race

[logician]

Help! I still have not been able to fix the clutch in my '70 vintage 911 gearbox, and I've got a race this weekend that I will miss if I can't resolve the problem. The clutch has problems releasing. Here is my question.

The factory manual specifies a throw of .6" at the clutch lever. However, I seem to get only .4". I've replaced the clutch cable, clevis pin, clutch fork, and verified that the pedal assembly is not faulty. I'm pretty sure the adjustments at both ends of the cable are done correctly. Question: is the factory manual wrong, and do others with '70 vintage gearbox measure only .4", throw even though the factory specifies .6"? How can I tell if the correct lever at the pedal shaft is installed? I've read that lever varied for different years. Maybe my car has the wrong lever.

-Juan

[daloff]

Make sure you have indexed the lever on the bottom of the transmission properly.
David

[logician]

David, there is no way to index the lever in a 901/911 gearbox. The design is different than a 915, which is what you are probaby thinking of.

Any help guys? My race is tomorrow.

-Juan

[Grady Clay]

Juan,

When arm fully actuated, is the clutch completely released?

When arm fully released, is there free-play?

Best,
Grady

[wevoid]

Juan,

I spoke to Brian last night about this, not sure what time today you will see him?

One thing to check - check where the outer cable mounts to the bulkhead, just where the cable exits the tunnel. This mount collar area can crack and allow the outer cable to move back and forth - losing some of the clutch travel potential. It becomes a spring in the system - behaving like cable stretch.

Hopefully we will see you tomorrow.

Regards

Hayden

[logician]

Grady,

I've tightened the rear cable adjuster until there is no free play at the pedal. The front adjuster on the clevis is set to 20mm, in the middle of the factory range. The clutch disk and pressure plate thickness are pretty close to new specification.

The clutch is engaging very close to the floor. When the clutch is pushed to the floor, it still drags just a bit, as the transmission is balky, and reverse grinds even after putting it into 1st or 2nd to stop the gears. I have also jacked the car up and watched the rear wheels rotate even when the clutch pedal is pushed down all the way. The disenagement is better when the car is cold.

It bugs me that the throw at the clutch release arm is so far off the specification, and I'm thinking that maybe the shaft/lever at the pedal is not the right one for my vintage. I remember reading in a previous thread that the geometry of that lever varied for different years. If not that, then I'm thinking there might something funky about the pressure plate. But I don't see how that could affect the throw.

-Juan

[logician]

Hayden, Thanks for the suggestion. I'll check that outer cable mount today. I'm heading to the shop shortly. I hope to see you tomorrow also!

-Juan

[Grady Clay]

Juan,

While you have it adjusted this way (no free-play yet barely releasing), what are the clearances between the arm and the casting at each extreme (pedal fully depresses and fully up)? Are both pedal stops proper?

I agree; it is starting to sound like there might be an unfavorable combination of the pedal assembly cross-shaft lever arm. I used to have all these measurements – long ago. When I posted on the different lever arms, did I list the Porsche P/Ns? Perhaps the guys who rebuild the exchange pedal assemblies for Pelican Parts can help.

I assume you confirmed the Bowden tube seat at the chassis is OK?

Best,
Grady

[logician]

I was hopeful when I found a fractured tube in the pedal box. I replaced that part and a few bushings (bronze), and that increased the throw to .5", which is still a little short of the .6" factory spec. But the problem is not fixed, although it is a little better now. The bowden tube seat looks good.

Grady, The fork lever does not hit the casting or the pressure plate at ether extreme of the pedal. I don't understand what you are asking about the pedal stops.

-Juan

[Grady Clay]

Juan,

About the clutch pedal stops:
There is a crimped rubber piece that limits the pedal’s upward movement (it also limits the brake pedal’s upward movement.) It isn’t normally adjustable.
There is also the adjustable stop on the wood floorboard.

The issue with the Bowden tube seat can be insidious. When the clutch is actuated the pressure from the tube can open up a crack. When the pressure is released, the crack “springs” back closed and becomes almost invisible. All it takes is for this to move a few thousandths and it is amplified at the clutch arm.

Still another thought is the cable tube in the chassis. It has an “S” bend in it and is brazed to the pan. The brazing can fail, allowing the tube to straighten slightly under pressure, causing these symptoms. Also the tube can wear through at the bends from lack of grease. Usually this causes a stiff pedal.

When you were into the pedal assembly, did you measure the length of the clutch arm?

Best,
Grady

[Grady Clay]

Juan,

What did you do about the support ring on the
differential cover for the Bowden tube, this thread?

IMAGE: ClutchTO70d.jpg


Best,
Grady

[logician]

Grady,

The upper stop is good. It was just replaced. I don't have a lower stop on the wood floorboard. However the clutch pedal can screw in and out of the lever, which acts as a stop. There is about 1/4" further pedal movement that I can get by unscrewing it all the way. I tried that previously, and found that the pedal movement is way too much.

The picture you have is not of my transmission. It is of my friends. However, that mount is broken on my sidecover too. The PO added a bracket attached using the nearest cover stud to constrain the cable end. That bracket seems to work pretty well, as the cable moves right along the remaining seat of the original mount.

I watched the action of that whole cable mechanism, all the way from the bowden tube seat to the fork lever, and the action looks good when I have someone step on the clutch pedal. The bowden tube seat does not move at all.

Question: can the tube in the transmission tunnel be replaced? Does it have to be cut out and welded in? I presume that the bowden tube seat is the end of that tube. Yes?

I'm coming to the conclusion that the problem is within the clutch, either the pressure plate, the disk, or the TOB. I guess it's time to pull the engine and tranny again and have a second look at those parts. I'd replace them all, but that damn TOB costs north of $400!

-Juan

[randywebb]

For everyone viewing this thread ... that pic IMAGE: ClutchTO70d.jpg shows a really bad support ring on the tranny. In other threads, Grady has posted on how to fix these with a dismountable/replaceable one.

Juan - I think you need to do the easiest checks next.... unfortunately, easiest right now is to R&R...

[Grady Clay]

Juan,

Here are some images so we are talking about the same thing.

The red arrows are the upward stop for the clutch (and brake)
pedal. The # 33 is the rubber stop and is crimped in place on
#32 where the arrow points. The protrusion on the clutch pedal
part #39 (short red arrow) contacts the rubber piece #33. (The
pin on the brake pedal #46, other short red arrow, contacts the
rubber piece #33 also.)

The greed arrows are the adjustable stop on the plywood
floorboard that limits the travel depressing the clutch.

The yellow arrow is the dimension we need to be concerned
with. There are several (three that I remember) different
lengths. I think there were two versions ’68 and earlier, at
least one different for ’69, different in ’70-‘71, and some
different again ’72 and later. Some of these lever arms of
#37 do not have the “kink” in them but are straight.
IMAGE: PedalAssy01b.jpg"
"
© Dr. Ing. h.c. F. Porsche A.G.

IMAGE: PedalAssy101b.jpg”
"
© 2001, Wayne R. Dempsey, 101 Projects for Your Porsche 911


For a track-only application, you could fabricate a longer lever arm
and weld it to the part of the existing arm. You could make it as
long as possible, just so the arm or cable doesn’t interfere with
the tunnel.

The stock system should be working.

We need to find the cause rather than some “fix.” If we don’t,
the “cause” will just become a bigger problem.

Yes, the cable tube is welded (brazed I think) inside the tunnel.
Someone posted a cut-away image of the tunnel within the
past year or so. Fortunately I have never had to repair
one – it doesn’t look easy.


Did you inspect your syncros, gear dogs and sliding sleeves
after you had the clutch problem? Remember my admonition
in your thread I linked above.


Best,
Grady

EDIT to correct punctuation

[Grady Clay]

Any Progress?

Best,
Grady

[logician]

Grady,

Thanks for the detailed reply an pictures. I haven't done much on the clutch because I've been tied up at the track all weekend. Even though I couldn't race, I went to visit with everyone, and took some great videos of the race. I'll post them later this week in the racing form.

That stop, #71 & 71, exists on my floorboard, but it is not limiting the throw. It is the bottom of part #43 that limits the throw, as it hits the floor.

The lever arm on my part #37 is straight, not kinked. I have not yet measured it. I would really like to see one from a '70/71 to compare. Anyone have a picture they could share? I am not inclined to modify mine if it is the correct one. As you point out, the stock system should be working, so there is something else broken that I need to figure out. I'm going to pull the engine and tranny again to have a look at the clutch disk, pressure plate, and TOB. I'll report what I find when I do that in the next few weeks.

I haven't had a look inside the transmission.

-Juan

[Porsche Doc]

Has the petal cluster been rebuilt in the last couple of years.
Did they use the weltmister kit? There is a problems with with the roll pin that is on the clutch arm. It is supposed to be hardened.
BUT we have encountered them shearing off. And the symptoms are the same your describing.
They slowly shear and the more you adjust the more it shears it , TILL it breaks totally.
Good luck man!

[logician]

Don, The roll pin was OK. I rebuilt the pedal cluster last Friday as I found one of the tubes was factured and needed to be replaced. That increased the movement at the release lever to .5", but still the clutch appears not to release fully. Actually, maybe a better description is that the clutch appears to drag even when the pedal is pushed in all the way (and adjusted for zero free play.)

-Juan

[logician]

OK, so after taking a week off after the end of the season, I looked at the clutch again, and this is my report/question.

After repairing the pedal cluster, replacing the clutch cable, and also pulling the engine to replace the clutch fork, I get .5" of travel when the cable is adjusted to give .5" of free play at the pedal. The pedal seems to engage at a reasonable height off of the floor -- about half way between from floor. Probably the fracture in the pedal cluster was the failure that caused the clutch to malfunction at the track.

But I'm still having a problem with what I can best describe as the clutch dragging. The draging interferes with shifting. With the clutch pedal fully depressed, it is a bit difficult to get into gear. 1st is worst. Reverse grinds, even after putting it into first in order to stop the gears. Actually, you can kind of hear that the gears continue to being driven when gently grinding reverse. The forward gears are also balky. I tried jacking the rear wheels off the ground, and you can see that they are driven a little bit even with the clutch fully depressed. The drive isn't very strong, as it can be stopped by hand.

The drag action seems to not happen when I first start the car, but it gets worse after driving around the block. Lifting the pedal an inch off the floor does not seem to increase the drag.

Any suggestions? What can cause the clutch to drag? My mechanic urged me to check to pilot bearing. But it's hard to see how that could apply much force to the transmission.

-Juan

[Early_S_Man]

When you had the pedal assembly apart ... was there any sign of repair at the shaft-to-hook junction? I have seen sloppy positioning of the hook at the end of the shaft [wrong angle] and then welded up, couldn't achieve full cable travel ... symptoms same as yours, dragging clutch and grinding in reverse that couldn't be adjusted out! Replaced the shaft and problem was fixed!