1970 911T Clutch "disconnected"

[kennyt]

Hi there
I had a problem last week where I was stranded with a suspected broken clutch cable on a 1970 911T with the infamous 901 push clutch setup.

I have only recently started driving the car after a long (14 year ) project to get it on the road and the motor was last reinstalled by a Porsche specialist (after a rebuild which excluded a new clutch assembly ) about 4 years ago . The thrust bearing (TO) was a bit noisy when pressure was applied to the pedal , but other than that , the clutch seemed to be operating well with a relatively light operation although I had a lot of play on the gear shift which I just recently fixed with some new bushes. (another mini project )

On inspection I found the cable was fine but the T.O. Fork had no tension from the TO bearing / clutch
I was able to move the T.O. Fork around (normally feels like it is attached to the TO ) and so thought something must have broke - so as good a time as any to replace the TO bearing and clutch and fix whatever was broken.

It was dropped off at the workshop and the guys were surprised that the engine came out with the clutch and pressure plate and TO bearing all still attached to the engine without having to release the TO bearing tension etc. as is normally necessary with the push type clutch.

The TO bearing still looks fine mechanically - the "ears" are still in tact and there is no sign of anything broken. ? (I am replacing it with a new one )
So my question are :
1 how does the TO Fork stay attached to the TO bearing ?
2 if the TO Fork uses the "ears" on the TO bearing to stay attached what stops the TO bearing from turning and "decoupling from the TO Fork ?
3 In pictures of the TO fork I have seen, some have a notch or small hook on the ends of the fork (like you see with a VW beetle) but then there are some with no notches like mine - has this part been improved - (and why ?)
4 Should I replace it or do I just stick it all back together as per the manual ?

Also - does anyone have a link on this forum which indicates what to check for BEFORE reinstalling the motor and clutch ? I have read about the fork travel and washer thicknesses for the TO fork etc - I have the Haynes manual but it is a bit cryptic (probably my problem - not the book )

[kennyt]

A quick correction - " 1970 Porsche moved to a 225mm pull-type design, in which the pressure plate is pulled away from the flywheel in order to release pressure on the disc. " - this is what I have - looking at the tech article on the forum.

[kennyt]

I found another article relating to "We have broken 20 or so throwout bearing arm spring plates that go under the throwout bearing arm pivot ball and maintain pressure on the throwout bearing arm."

I found this pic and I think the spring labelled #2 is missing / broken - this would make more sense to me - will check with the workshop

[kennyt]

Well - I checked this morning and it is not the spring ?

Anyone know how the fork attaches to the TO bearing an the possible reason it got disconnected ?

And how do we go about reinstalling the engine so that it does not reoccur ?

[Trackrash]

So, you are saying that the release arm pivot is still intact? Amazing. AHIK.

At any rate. The throwout bearing is installed by placing it through the release arm and then ROTATING it 90 degrees after the trans is bolted to the motor. This will in essence lock it in place.

Are you saying that the repair shop/ "mechanic" did not know this or even consult the manual?

OK, so the question is how did the TO bearing come loose from the release arm?
Good question. I can only imagine that the clutch cable broke or was VERY loose allowing enough slack for the TO bearing to be able to move back and be able to rotate.

[Trackrash]

[kennyt]

Thanks for the reply Gordon - still a mystery
The repair shop removed the engine without removing the tranny by simply unbolting it and sliding it back - they were expecting the TO to prevent it from coming out but it seems it had turned the 90 deg - I assume we will have to drop the tranny and reassemble by mating the engine and tranny before reinstalling it in the car based on the stuff I have read so far regarding the 2 holes at the top of the bell housing where you gain access to the TO bearing to turn it into place -
I have the Haynes manual but it only shows the pre "70 and post '72 and was hoping I could find some specifics on what to check once the new clutch and TO beraing are installed
I have read about having 25mm of travel on the TO fork - and this needs to be adjusted by the thickness of the washer on the TO fork pivot - 5mm or 6mm depending on the thickness/wear of the pressure plate ?
I have searched the forum and there have been some references to previous posts regarding correct assembly / installation / adjustment of the new clutch but have not found anything which outlines it step by step

For now ( based on what I have read in a couple of threads ) my plan is is follows :
Remove the tranny - so we can mate the engine and tranny before installation
Attach the new clutch assembly to the motor - with center tool in place
Attach the TO bearing to the pressure plate
Turn the TO bearing 90 deg of the TO fork
Mate the tranny and engine
Turn the TO bearing through the rear holes 90 deg into the TO fork

This is where it gets a bit foggy
Check the TO Fork travel is 25 mm (is this the full throw from engaged to disengaged ???)
If not - change washer on TO fork pivot - 5mm to 6mm depending on amount of additional travel ???
Then install tranny and motor into the car
Attach clutch cable and adjust clutch cable - I found an article on this procedure

Cheers

[gamin]

1970 Porsche factory workshop manual. Section 1, page one, paragraph 1. Engine and transaxle are removed AS A UNIT. They are separated once removed from the car. Had a Porsche dealer
leave the trans in the car. They complained about difficulty removing engine from trans in the car.
They had to replace the rear engine tin they ruined. Idiots. Your shop should make you whole for no charge.
When in doubt, read the instructions.

[kennyt]

Thanks Gary -
But I only have the Haynes manual - hence my cry for help on this awesome forum - I am always amazed at the help and experience of the members -
any chance you can relay the instructions from your workshop manual ?

[Trackrash]

As far as your plans go, I have a couple of suggestions.

If the TO bearing is off the pressure plate, check its fit on the release arm. Make sure it locks in place when turned the 90 deg.

Also make sure everything is up to spec. Check the pressure plate and its fingers where the TO bearing mounts is good and the clutch disk itself is good.

The washers under the pivot usually don't need to be adjusted. You can check if they are good by removing the pivot and checking the wear pattern on the pivot. If the wear pattern is even you are good. You want the release arm to not be cocked one way or another which would put stress on the pivot.

While in there check the pivot for wear. If you have one of the brass coated ones and it is not worn KEEP IT. The replacements are only steel and DONT LAST. AHIK.

The TO bearing must be attached to the PP when the PP is removed.

Once you have everything together and have turned the TO bearing to lock it in place, you may want to use a small wood block or shim to keep the release arm from moving and allowing the TO bearing to come off before you have the cable installed.

You can check the operation of the clutch before you install the engine/trans in the car by prying the release arm and watching through the holes in the top of the housing.

Good luck.

[kennyt]

OK - so this is where we are now
The guys removed the tranny - and installed new TO bearing and new clutch plate - not much wear on the old one but I decided that if it is apart we may as well replace it.
Attached TO to fork as directed (through the rear holes and all looked good - re installed motor and tranny and did cable adjustment - then on first attempt the TO bearing "disconnected" so we must have another problem
All the images I have been able to find of the TO fork have raised "hooks" on the TO bearing end but the one on my car is just flat - see images above ?
Could this be the problem ?
Mine is the first image

[kennyt]

Well it's not the wrong TO fork or washer or spring (just bought a new spring#4 and the Washer #3 looks correct from a parts search and there is no visible wear on the TO fork and it fits snugly over the new TO bearing

[kennyt]

[Trackrash]

This is my old setup. When my TO bearing is placed on the release arm, it won't turn.

[kennyt]

Mine also fits snug onto the TO bearing when removed from the gearbox

So we tried re-attaching the tranny to the motor with the original porsche #3 washer and #4 spring and the TO goes into the release arm very easily - we did it by sliding the pressure plate and clutch plate onto the tranny spogot shaft first (then mated the engine and tranny ) - and then slowly tightened up the pressure plate onto the flywheel through the starter motor hole

Once all was torqued up there is about 3mm play/gap between the TO release arm and the #4 spring (without any the clutch cable attached ) ?

This doesn't seem right as there also does not seem to be enough space / throw for the TO release arm to disengage the clutch ?

We are going to try thinner washers (instead of the porsche #3 washer ) to get rid of this play/gap - the clutch plate is 10mm thick so maybe this is why the relative position of the TO is closer to the tranny - hence the need for a shorter (thinner washers ) and shorter pivot ?
The Porsche washer is 6mm thick so we are going to try 2 x 1,5mm washers

My question I guess is - without the cable attached should the TO release arm should there be any play once everything is tourqued up ?

[Trackrash]

FWIW, I just measured an almost new disk and mine is 8mm thick.

IIRC, it's been a while since I retired my 901, but with my trans installed on the engine, I could not disengage the release arm from the TO bearing, unless I used a prybar on to release arm. Otherwise there was enough tension to prevent it from coming loose, even without the cable attached.

Is your TO bearing contacting at the arrow in this picture? If so, you may have to adjust the washers to prevent it. Otherwise it could lead to your problem. That's my guess anyway.

[kennyt]

Thanks Gordon for all your help

Looks like reducing the washer thickness to 4mm did the trick

No wonder they moved away from this setup

Cheers Kenny

[Tom Elder]

Old thread but I am having a similar issue, new thicker friction disc, there is not enough tension between the throw out bearing and the clutch fork. I have reduce the 6mm washer to 5mm, slightly better but may have to reduce further. I will pull the tranny off again but I would also like to check the thickness of the nubs on the end of the fork. Any body have one in good shape, can you check the dimension for me. Thank in advanced
Cheers

[tk32]

I have a fork in very good condition (possibly new-old-stock) kicking around the garage and will dig it out. Looks like yours has been welded and repaired at some point?

The problem is my calipers and the fork are in different locations, dang tools spread all over the place right now with various projects. I can get that dimension to you in a few days if no one else gets back to you sooner

[stownsen914]

It's possible your clutch fork is slightly bent and someone tried to accommodate that by welding the nubs. Geometry is important of course. What is the thickness of this disk? Is it non-stock / thicker?