1970 911 clutch problem

bertj · 03-31-2004, 10:33 AM

Hello,

I've had problems getting the correct clutch adjustment on my 1970 911T with the 901 type transmission. Per the Haynes manual, I adjusted the clutch pedal free play to 25 mm. But I find it hard to shift gears at this adjustment. I have to push the clutch pedal in, wait one to two seconds, then shift up to gain a positive clean shift. If I don't wait between gears, then the shift has resistance. I have been shifting carefully to avoid grinding the gears.

The Haynes manual says that the throw out fork should travel 15 mm to completely disengage the clutch. I measured my throw out fork travel to only 11 mm with the clutch pedal free play set at 25 mm. So I adjusted the pedal free play to 10 mm and found the fork travel moved up to 14 mm. But the clutch feels "tight" and it takes more effort to push the clutch in. It just doesn't feel right to me and there must be something wrong if I can't adjust to the factory spec.

The Transmission was rebuilt about 4,000 miles ago. The following parts were replaced at the same time or a little bit after the tranny rebuild:

- Clutch Cable
- Pedal assembly bushings – bronze type
- Shift Rod Coupler
- Shifter Ball Cup & Bushing
- New Bushing fabricated for the transmission Side Cover where the clutch cable feeds through to the trunion end.
- Pressure Plate
- Clutch Disk
- T.O. Bearing
- Pilot Bearing
- T.O. Bearing Guide Tube
- Flywheel & Flywheel Bolts
- Pivot Ball under the T.O. Arm (aftermarket chrome-moly unit)
- Flat Spring and Washer under the Pivot Bolt.
- Aluminum Trunion

I've replaced everything except the T.O. Fork, but I couldn't find any problems with it when I had the clutch apart. It didn't appear bent or cracked. There was no apparent galling where the fork connects to the pivot bolt. It looks shiny from contact, but no metal has been grinded away.

- Should I have 15 mm of T.O. Fork travel per the Haynes manual or is less travel okay?
- The tranny was rebuilt recently (4000 miles ago). Do I need to break in the syncros for a certain amount of time or mileage?
- How do I know if my T.O. Fork is good? Is it more likely to bend or crack? Could it “flex” only under pressure and that’s why I don’t notice any problems visually?
- The T.O. Fork looks solid. Is this a common part to replace on the 1970/71 911?
- The Pressure Plate looks okay to me. Is there anything to check for that would point to failure?

I would appreciate any input or experiences from other PO’s with this same problem.

See the attached photo of my T.O. Fork for reference.

Thanks,

bertj · 03-31-2004, 10:40 AM

Here's the side view of my T.O. Fork.

bertj · 03-31-2004, 10:42 AM

Photo #3

bertj · 03-31-2004, 10:43 AM

Photo #4

Early_S_Man · 03-31-2004, 10:46 AM

Bert,

15 mm probably is a bit too tight ... but, I guess it depends on how you define 'freeplay' ???

On thing for certain ... you don't want the fork pushing against the throwout bearing at all times! So, I would back off on the freeplay to about 17 mm - 19 mm, which is where I tend to like it set.

bertj · 03-31-2004, 11:18 AM

Hello Warren,

Quote:

15 mm probably is a bit too tight ... but, I guess it depends on how you define 'freeplay' ???

The clutch pedal normally sits forward of the brake pedal by about 25 mm. I measure the distance from the forward position of the clutch pedal to where I can pull it back it back to an even position with the brake pedal. My freeplay measurement is now 10 mm, which gives me 14 mm of T.O. fork travel. I agree this is too tight and the T.O. Bearing is probably under constant tension. I'll back it off, but the T.O. Fork is not moving enough to completely disengage the clutch. Thus the hard shifting.

Thanks,

Early_S_Man · 11:33 AM

Bert,

There are several points in the clutch cable system where excessive wear can add play, and can be checked or fixed without pulling the transaxle again ...

1. Pedal box bushings

2. Clutch pedal arm hole/eyelet for clevis pin

3. Clutch cable clevis pin

4. 1970 - 71 only -- pulley & shaft at side of transaxle

5. Clutch cable end pivot 'fitting' ...

bertj · 03-31-2004, 11:45 AM

Quote:

There are several points in the clutch cable system where excessive wear can add play, and can be checked or fixed without pulling the transaxle again ...

Warren,

I'll give answers to what I've worked on below:

1. Pedal box bushings - replaced with bronze bushings a couple of years ago. They look fine. No play or wear.

2. Clutch pedal arm hole/eyelet for clevis pin - the bushing for this arm hole has worn in the past and I recently replaced it.

3. Clutch cable clevis pin - replaced and fine.

4. 1970 - 71 only -- pulley & shaft at side of transaxle - not sure what you mean? My clutch cable travels through a bushing attached to the transaxle side cover. I had a machinist friend create a new one. The old bushing had a lot of slop.

5. Clutch cable end pivot 'fitting' ... - I replaced the factory plastic trunion with an aluminum aftermarket piece. It looks fine.

Have you had any experience with a bent or cracked T.O. fork?

Thanks,

john70t · 01:12 PM

bertj: sorry, too many specifics to comment on any of the great details above.
The basic idea to adjust the unique 70-71 Pull-clutch is that you can pull the pedal UP about 1 1/2". I think this is around the proper freeplay for the 70 and 71 pull-type clutch. Most push-types give pedal freeplay about an inch or so downwards!

Regardless, providing everything is rebuilt as specified by California transmission-rebuild law......
-if the clutch doesn't have enough release action and it grinds, tighten the cable.
-if the clutch has too much release action and the clutch slips, loosen the cable.

A good clutch has a strong, but controllable, grip a few inches from the floor(about 10-25% of total travel). The cable and pedal stop are adjustable,
the fine tuning is up to you. Everything acts independantly.
Nice pics and post BTW.

Early_S_Man · 03-31-2004, 12:13 PM

Sorry about the 'pulley' reference ... must have been thinking about 914 clutch cable routing!

bertj · 03-31-2004, 05:03 PM

Anyone else experience this problem with a 1970/71 clutch?

Please see my earlier post for details.

Thanks,

Zeke · 03-31-2004, 07:01 PM

I'm going to go out on a limb here and apply some 914 901 knowledge in the hopes that something I say will trigger a response from someone who can zoom right in on the problem.

The new disc and pressure plate combined have a much greater thickness than what came out, I assume this, or you wouldn't have replaced the PP, only resurfaced. This puts the angle of the fork different than it was and can have an effect on the leverage and travel. The correction was to move the pivot point of the fork.

On the 914, this was done with a washer under the pivot ball. HTH.

bertj · 04-01-2004, 11:27 AM

Thanks for your post Zeke.

I was thinking about moving the pivot bolt as you said. The flywheel, disk and pressure plate are new and thus there is added thickness. But if everything in my clutch is stock do I need to modify the pivot bolt position? I thought the pivot bolt position needed to be modified only if something was out of spec. Something like the flywheel being too thin.

I am concerned that the T.O. Fork is bent and out of spec. I don't want to spend the money on a new fork if it is okay.

I am wondering if other PO's of the 1970/71 911 had to replace the T.O. Fork as part of their clutch job. My car has 124,000 miles on it, maybe the fork is fatigued??

Early_S_Man · 04-01-2004, 12:57 PM

Bert,

That fork looks pristene to me, so I don't really befieve that is the problem.

And, no, I don't believe any adjustment in the pivot is needed with all new parts!

How long have you been driving a car with Porsche-patented synchronizers ... 356, 914, 912, 911, etc. ??? There is a definite 'pause' needed between gears, perhaps half a second, minimum, IMHO.

My suggestion is to back off the adjustment about 1/2 turn, i.e., 0.5 mm from the 'tight' point, and drive the car a while.

bertj · 04-01-2004, 01:14 PM

Thanks for your posts Warren.

This is my first Porsche, but I've been driving it for 11 years. I don't shift fast in general as I have gotten used to the Porsche syncros. I used to wait half a second between shifts and it worked fine in the beginning. My clutch would shift normally with the normal 25 mm clutch pedal free play as specified by the Haynes manual. Now I have to tighten the cable to 10 mm of free play and this is with new clutch parts.

Something doesn't feel right in my current setup and the only original part left is the T.O. Fork. I agree that the fork looks good, but I wonder if the T.O. Fork could be slightly bent or it would bend under load only.

Another thing I noticed was that the guide tube for the T.O. Bearing had a wear groove ground into it. I wasn't sure what caused this groove, but I replaced the guide tube with everything else. Now I am wondering if the T.O. fork was bent, then the fork would have pull the T.O. bearing to one side of the guide tube. Thus the T.O. bearing would be off center and not allow complete disengagement of the clutch. Does this make sense?

Thanks,

john70t · 04-01-2004, 01:39 PM

Your right, that does sound like an out-of-round/wedge-shaped fork pivot ball or mabye the cable is being pulled from an angle it's not supposed to be.....as if the fork was too long, or the pivot location shifted.
This is a good puzzler. A machine shop could probably magnaflux it, but parts bending under load doesn't sound "porsche". I was thinking mabye one half of the clutch cover fingers were soft and this caused the side-loading(?)

bertj · 04-01-2004, 03:25 PM

Thanks for your posts John.

My pressure plate is only 4000 miles old and the fingers of the diaphram springs did not look bent. I will have to check if one side is soft or distorted.

The pivot ball looks fine without any distortion and it fits inside the T.O. fork without slop.

Have you heard or read of 1970/71 T.O. arms bending or cracking?

Thanks,