Considering another tranny project, 70-71 901 in a 914 Options

[Red-Beard]

The late 901 and the 915 use the same style clutch and it's a 225 clutch, so it's more capable, HP wise.

Internally, the 70-71 901 is the same as the early 914 901. Doing a sideshift conversion on one of these would be relatively easy.

What is the clutch cable setup for the 915 in a 914?

[ClayPerrine]

I have been preaching about this for a while. The clutch is a bastard setup, not hard just a mismash of parts.

You have to use a throwout bearing and clutch disk from a 70-71 911. The disk has the correct splines for a 901 but it is 225 mm in diameter. The throwout bearing is a special piece to match the clutch fork. The rest of the clutch pieces can come from any pull type clutch setup.

You will also need to machine the clutch pivot mount hole in the case. You have to add a steel T shaped insert, pressed in from the INSIDE. This will keep the threads from pulling out of the case when you use a stronger 911 pressure plate. Then you have to get an after market clutch pivot. The stock ones break.

The cable is from a 75 911, and it will bolt in. Use the 914 clutch trunion, and you are set.

[Red-Beard]

Do you have a source for the pivot and the threded insert?

I was actually just planning to buy a 1970/1971 911 901 and do a sideshift conversion. This sounds easier.

Clutch disk is 225. Pressure plate the same or do I need a 911 one as well? What about the flywheel? Will the stock 6 fly wheel work fine?

James

[ClayPerrine]

Using the70-71 911 trans is the way to go. All you have to do is swap in the side shift parts from a 914 trans. That is what I am doing. I already have the transmission. If you use a 914 trans, you have to move the clutch pivot point 14 mm and find the clutch fork from the 70-71 911.

The pivot can be bought from Pelican, or Mid America, or any of the other P-car parts suppliers out there. The insert will have to me made by a machinist,but considering that it's just a piece of stee bar stock turned and tapped, it should be farily cheap. The problem is that unless you use a 2.2 pressure plate, the stress is too much for the threads in the magnesium case of the 901 trans. Putting a steel insert with a large flange on the backside spreads out the load, and provides steel threads for the pivot.

The Flywheel can come from any 911 that uses a pull type clutch, as can the pressure plate. It is a flat flywheel. The 914/6 flywheel is a cup type, and can't be used with this setup.

[bondo]

QUOTE (ClayPerrine @ Jan 10 2005, 06:43 AM)

You will also need to machine the clutch pivot mount hole in the case. You have to add a steel T shaped insert, pressed in from the INSIDE. This will keep the threads from pulling out of the case when you use a stronger 911 pressure plate. Then you have to get an after market clutch pivot. The stock ones break.

For my V8 I'm going to use a 228mm clutch and flywheel from kennedy.. Do I need to worry about any of this clutch pivot stuff, or does it only apply to using 911 parts?

[Red-Beard]

Hmmm. I wonder if a Case Saver would work well...

[Downunderman]

No it doesn't. I have proved it and torn the time cert out of the case. I ended up boring a hole through the centre of the pivot ball and bolting it to the case with an aluminium top hat in the front of the diff housing.

[bondo]

I'm lost.. Could someone explain what the whole pull-type push-type thing is referring to, and why the pivots break?

[ClayPerrine]

The 1969 and older 911 used the same clutch setup as a 914. The pressure plate is the push type... meaning that the throwout bearing presses against the pressure plate fingers to release the clutch. Because of the design, we have what is called a 2 step flywheel, meaning the friction surface the clutch disk contacts is different from the surface that the pressure plate bolts onto. If you don't machine both the disk surface and the mounting shoulder when resurfacing the flywheel, you can cause problems with the clutch functioning correctly Plus, the shoulder limits the size of the clutch disk to 215mm.

In 1970, Porsche reengineered the clutch in the 911. They made a larger 225mm disk to handle more power, and changed the pressure plate to a "pull" type. This means that the throwout bearing is fastened to the clutch fingers, and the clutch fork pulls it away from the flywheel to disengage the clutch. Ths also has the added benefit of more clamping force on the disk. With the exception of the engines with the "dual mass" flywheel, this same basic setup was used up until the 993 was released.

In 1970 and 1971, Porsche used a 901 in the 911 with the pull type clutch. Because the new clutch was stronger than the old push type, the engineers underestimated the requirements for the clutch fork pivot. The factory ones break off. There is an aftermarket one that is stronger and doesn't break. But now the stress is passed to the threads in the transmission case. The only fix for that is to put in a T shaped or tophat insert. This provides steel threads for the pivot, and spreads the pullling load across the inside of the case. a 10mm hole with a 15mm diameter end on it pressed in from the inside of the transmission case will prevent the threads for the clutch pivot from pulling out ever again.


Hope that explanation is what you were looking for.

[bondo]

Exactly what I needed! So if I understand this right, the pivot fails because it was intended to be pushed on, but switching to the pull type pulls on it. Which would mean the aforementioned pivot mod doesn't apply to the KEP clutches because they are push type.. right?

Thanks for the explanation!

[ClayPerrine]

The KEP clutch is an adaptation of the push clutch. You won't have a pivot point failure on it.