Clutch Spline Question

[JPM]

I have a 901 transmission, off a 69 911T, which is mating with a 2.4S engine and I have already installed the later 2 piece flywheel. To match, I have ordered a 72 225mm pressure plate/clutch combination. A similar 225mm plate/clutch is available for 70-71 models which have the 901 tranny, but at a higher price, which is why I chose the 72 version. 72 is the year the 915 transmission began. Is there a difference in clutch spline size between the 901/915 transmissions, if so I should probably get the 70 version. 69T has a 215mm clutch mated to a one piece flywheel.

Thanks,

[66S]

72 and later have a different spline for the type 915 transmission and wont work for 70-71. Also a 69 trans needs a 215 clutch and flywheel because it lacks the provisions for a 225mm clutch.

[Frank Beck]

The engine doesn't care what flywheel/clutch you use.
The transmission cares a lot.

Trans, not the engine determines flywheel and clutch type.

Because of the release fork and pivot you're stuck with using the 215mm flywheel and clutch. If it's a race car we make an alum flywheel that uses a 5.5" single or 2-disc clutch. If its a street car go with a Kennedy pressure plate if you're concerned with clamping pressure.

[JPM]

72 and later have a different spline for the type 915 transmission and wont work for 70-71.

Get it, 915 clutch won't work in 901 trans.

[JPM]

Because of the release fork and pivot you're stuck with using the 215mm flywheel and clutch. If it's a race car we make an alum flywheel that uses a 5.5" single or 2-disc clutch. If its a street car go with a Kennedy pressure plate if you're concerned with clamping pressure.

Thanks but that is not music to my ears, unfortunately. How do the 70-71 avoid interference using the 225mm clutch since they use the same 901 trans ?

[Jon B]

How do the 70-71 avoid interference using the 225mm clutch since they use the same 901 trans ?

It's not an interference issue, it's a clutch compatibility issue.
A 69 transmission is set-up for a push-type clutch, a 70/71 for a pull-type clutch. That's what Frank is referring to by "release fork and pivot".

A 69 transmission is a 901, a 70/71 is not.

Jon B.
Vista, CA

[JPM]

I get it on the push/pull versions of the 901 trans, but what do others do about adapting bigger engines to their early 911's, other than the Kennedy clutch suggested by Frank.

[Jon B]

I get it on the push/pull versions of the 901 trans, but what do others do about adapting bigger engines to their early 911's, other than the Kennedy clutch suggested by Frank.

If the engine has a 6-bolt crankshaft, use an early flywheel and clutch (65-69 or 914/6) with your 69 transmission.
If you want to use a later flywheel and clutch, you need to use a later transmission or re-case yours.

Jon B.
Vista, CA

[JPM]

Okay thanks guys, I guess I'll have to use my early flywheel and clutch. Save some cash too.

[JPM]

Just an update in case this can benefit anyone else. When dealing with earlier transmissions like the 901/911, the problem lies in the weak first gear. Some have solved this by converting to a 4 speed with tall ratios and according to Kennedy, with a V8, get rid of first gear and change the ratios of 4th and 5th to make it a 4 speed.
So you are faced with breaking 1st gear with too much pressure or slipping in 1st with too much power. I have decide to follow Frank Beck's suggestion and take a chance with the Kennedy stage 1 pressure plate which ups the clamping pressure from 180 (stock) to 230 ft.lbs of torque. Thanks all for weighing in on this.