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cameron.arnott's Avatar
 
Join Date: Jun 2006
Location: Adelaide Australia
Posts: 886
911(901) Trans - Simplified diff + other questions

I'm preparing to rebuild my '71 911 trans and have been busy researching here to see what I should do. I'd like some clarification on the parts to order as a couple of the threads on this subject appear to differ slightly.

The parts I believe I need are:

Long bolts - 901.332.902.12 x 2 no 'nipples'
Armature - 911.332.208.00
Roll pin - 900.308.005.00

But I have also seen mentioned:

Hex Screw - 901.332.275.12 Are these also bolts similar to above?

Threaded piece - 911 332.206.1 x 2 Do I need these on a '71 trans?

The whole trans will be apart to change the gear sets so naturally gaskets etc will be changed at the same time.

Can someone please clarify for me?

I'm also thinking about buying another trans which I believe to be a 901/13 from a '69 to get the gears but are the differentials & stub axles interchangeable as well?

Lastly it will have a billet Alumium intermediate plate as soon as I work out which one to buy.

Any other upgrades that I have missed that should be done whilst it is in pieces?

Thanks for your input!

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Old 07-21-2007, 08:31 PM
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Location: Arapahoe County, Colorado, USA
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I have two of these 911/01s apart for photographing and I just found a 901/13 that Im volunteering to rebuild for a local shop.

When you replace the intermediate plate, I recommend you check the pinion depth before and after. You may find you will need to change shims (metal and paper gasket) to get the pinion to remain in the same position. It is important to check pinion position prior to even loosening the nose casting.

One of these 911/01s was a virgin (had never been apart) and the pinion was exactly where the numbers said. The only problem is it was failing - only a little but still not usable.

Of the bearings in the transmission, I would ALWAYS replace the two ball bearings in the intermediate plate. Depending on condition, you might consider replacing all six bearings (a lot of work).


I dont think there is any difficulty updating your simplified differential. You should have the correct threaded pieces. (I think this is an issue with the early [alu case] differential.) You can even just grind off the tits on your stretch bolts (after you post images - please).

A 901/13 is a reasonable source for gears. I suspect you might consider buying an X 5th to replace the Z in the 901/13. Those are readily available and not expensive. You will like AFMSX.

You will notice that a 901/13 is not the same casting as the early 911/01 even though it is pressure cast magnesium. As near as I can tell, there are three distinctly different mag castings. Which 911/01 casting do you have? The key is the location of the transmission number and type number on the bottom rib (70 and early 71) or on a separate boss under the differential (from mid-71).


All of these mag castings suffer from a propensity to crack where the steel bearing carrier is cast in place. The crack never seems to have caused any problem other than a very minor oil leak. I have considered stop-drilling the crack and then adding epoxy. I havent tried this and have no experience. All of my 914-6 race 911/01s have the crack with no problem. Just something to worry about.

OK, on to preparing for your rebuild.

How does your 911/01 shift? Any syncro issues? Even if it shifts great, I suspect you will find damaged 1-R sliding sleeve, 1st engagement dogs, syncro, 2-3 sliding sleeve and related syncro parts.

During these years Porsche changed syncro parts very often. You should post images of what is in the transmissions. There can be a useful selection process of which parts to use. There are new parts you must use and there are some older used parts that perhaps are better. You have Pelican friends who can help.


A critical part of the transmission is the unique 70-71 clutch operation. The type 911 transmission will only survive with a properly operating clutch. This is more important than any detail in the transmission. A Pelican search will yield a lot.


What is your access to the ring & pinion and the other transmission tools? Even if not readily available, email me where they are. Perhaps from the other side of the world we can help make them available. Porsche didnt go to the effort to not have them used - here even almost 40 years later and the other side of the planet.

Best,
Grady
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Old 07-22-2007, 09:18 AM
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Hi Grady

Thank you again for your help. Unfortunately I wont be doing this rebuild myself, although having read many many of your threads in relation to these transmissions I would love to give it a try. Your offer to help with finding tools is very kind and greatly appreciated as well

My car is currently about 2000 miles away where it has been since the last event we entered. As well I am currently living in a property where I dont even have an undercover car park and my friends shed is currently full of his own race car project (Datsun unfortunately!)

The real issue with the trans seems to be second gear either going up from 1st or down from 3rd. Having read a lot of information here I'm also pretty keen to shorten the ratio's a bit from standard, add a billet intermediate plate and de-simplify the diff whilst its all apart.

This board is a wealth of useful information and I'd like to thank all the of the knowledgeable posters and particularly yourself for sharing your intimate knowledge with us all!
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'74 RS 3.0 Replica
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'70 911E Bahia Red SOLD
'71 911 S/T Replica 2.3 Twin plug BEAST SOLD
Old 07-24-2007, 04:08 PM
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I have broken the spider gears (90133290200) in my 1967 902/1 trans. I am looking for a reliable source for replacement parts. Any suggestions would be appreciated.
The car is a 1967 912 converted several years ago by Franz Blam in Georgia to a 1977 2.7. The 912 trans stood up well for over 7 years.
Old 07-30-2007, 05:34 PM
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Pm'd you with a lead.

Good luck

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'74 RS 3.0 Replica
Porsche 968 Clubsport SOLD
'70 911E Bahia Red SOLD
'71 911 S/T Replica 2.3 Twin plug BEAST SOLD
Old 07-30-2007, 11:47 PM
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