Building the optimal 901 transmission

[MichiganMat]

Im in the process of rebuilding our 901 transmission on our '67 912 project and I've got a few questions:

1.) I've heard the diff needs to be updated to the "simplified" design. True?
2.) I've got 2 different cases at the moment, one with the narrow intermediate plate and one with the widened plate from a 914. Should I build with the later wider case? Is there any advantage to it over the original narrow '67 case?
3.) What else do I need to be aware of concerning the 901?
4.) Where can I get torque specs on the input and output shaft nuts?
5.) How much horsepower can we expect to handle mated to a 901?

Thanks all

[djpateman]

The aluminum case 901 would be stronger than the magnesium 914 case, and original to the car. Output flanges will be correct.
If it is a 914 case, then the diff needs to be flipped, and a new vent location drilled.
What are the serial's from the two cases?
Get Dr Evil's rebuilding DVD.

[Grady Clay]

Originally Posted by MichiganMat

Im in the process of rebuilding our 901 transmission on our '67 912 project and I've got a few questions:

1.) I've heard the diff needs to be updated to the "simplified" design. True?
2.) I've got 2 different cases at the moment, one with the narrow intermediate plate and one with the widened plate from a 914. Should I build with the later wider case? Is there any advantage to it over the original narrow '67 case?
3.) What else do I need to be aware of concerning the 901?
4.) Where can I get torque specs on the input and output shaft nuts?
5.) How much horsepower can we expect to handle mated to a 901?

Thanks all

1.) No. The ‘simplified’ design differential needs to be updated. You can use the parts from the 914 differential.

2.) Yes, use the aluminum case transmission with the ‘narrow’ intermediate plate. That is a good, strong transmission compared to the 914-4.

3.) Don’t use first gear for ‘jackrabbit’ starts.
First is a gear to get the car easily rolling, not to apply lots of power.

4.) Get a photocopy or scan of Section “R” pages R1-R87 with Supplement pages SR1-SR172 of the 911 Workshop Manual, Vol. I.
The Porsche PET CD parts manual has great exploded diagrams.
This will have all the info you will need.
There is a lot here in the Pelican archives. The Search function is your friend.
The DVD is a great addition. I.

5.) I consider a 2.7 or 2.8 to be the limit for a type 901/911 – if you are careful.
Even then, the transmission must be ‘perfect’ and you will need an oil pump-filter-cooler system for extended high-power use.
Some think it acceptable to use a 3.0 or 3.2. I don’t.
This transmission was designed for a 1.6 & 2.0.

Best,
Grady

[RWebb]

#3 is b/c the gear is hung way out there by itself

- best upgrade to a 901 trans. is a typ 911 trans.

- how about a 904 mainshaft (or the upgrade aftermarket part that somebody makes...)

[MichiganMat]

Is it true that ring and pinions are ground to be paired up together? The pinion in my 901 box was badly gouged so I've used the pinion from my 914 box, but Id have to swap rings on the 901 diff and that seems complicated. Can I just continue to use the orig 901 diff with the 914 output shaft?

Thanks all.

[Jon B]

Pinions and ring gears are tested together for noise at various positions, the final adjustment marked and paired at that point. Adjustments vary quite a bit.

Running orphan gears of the same manufacturer together is possible, but not recommended. In your case, the 914/4 pinion was manufactured by Volkswagen, the 901 ring gear by Getrag or Hurth.

Have the 914 ring & pinion set up in your 901 by a Porsche or VW transmission shop in the bay area, or contact Pete Zimmerman in Bakersfield.