901 Transmission Question

[DUBSMK2]

hi I have a 1973 911 2.4 cis the transmission that came with it is 901[not installed] not the 915 that came with that year. my question is when I order a clutch kit am I buying flywheel pressure plate etc for the transmission or base on engine info.
or is it more it than that
any info will be grateful
Thanks

[Tom C.]

Do your research on this one. The 901 trans has two different clutch config's (901 and 911). To run one in a 73 I would guess you'd need to ensure all clutch components are correct from the pedal to the clutch release arm (yes they are different). Also check to see how your speedo is going to attach and make sure it's correct. If it was mine, I may consider selling the 901 and buying a correct 915 for the motor/car. If you don't get the setup correct, at a minimum, you will have trouble getting a proper clutch adjustment. Which is a PITA considering to fix it you've got to pull the motor again.

[Matt Monson]

Is the transmission that came with the car magnesium or aluminum? Either way, I would concur with Tom and get rid of it and get a 915 instead. In addtion to issues with the clutch/pp there could be issues with the drive flanges to the CV's as well as the shifter linkage.

If you want to consider going over to a 915, drop me a line. I run a Porsche tranny business and would consider your 901/911 transaxle as a core for exchange towards the purchase of one of our rebuilt 915 units. I can also help you with some of the linkage/clutch release items you may be missing. I don't currently have any '73 915's but I have other options that will work.

[RWebb]

The type 901/911 trans. is weaker than a 915 and more liable to break - esp. if you drag race or start off fast.

BUT it has the better, famous road-racing shift pattern, is lighter in wt., and feels better (lighter shifting) than a 915.

It can be a bit of bear to get one to work with the later cars -- the question is: how much effort (or money if you have a good shop nearby) are you willing to put in to get the adv.s above (and realizing the weakness of these rel. to a 915).???

The 1973 915 is not exactly a work of art (tho better than a '72). I have one I could sell if you want it (e.g. to have a "Stock" car). My advice if you get a 915 is to get a later year that still has the R&P for your year (a '74) - this will have a better input shaft seal design, make sure the issues re the guide tube are fixed, and to strengthen and rebuild the whole thing before installing it. That won't be cheap - there are 2 major strength issues (side cover, and internal bearing plate) to fix.

You are going to want to educate yourself on these transmissions. There is a great thread on the 915 with a table of the features for each year.

There is more info on Porsche transmissions on this bbs than in any book.

Good Luck!

[DUBSMK2]

seeing how each transmission have it's own faults some good some bad I do like the dogleg, my setup is stock no racing mods and already having this one what would I need to make it work I'm I buying the kit for transmission or for the engine

thanks

[jpnovak]

Before proceeding with your installation you need to post the tranny type and serial number that is stamped in the bottom rib or a stamping plate below the differential.

the tranny type will be 901/XX or 902/xx or 911/xx in nature. Once this is know it will define what clutch package, throw-out bearing, flywheel, clutch arm are needed.

[DUBSMK2]

numbers on the case are 4/66 901 301 101.or
on bottom 902/1 227935

[Tom C.]

But based on those numbers do you know if this tranny is a 4 speed or 5 speed?

It could be a 4 speed . . . I'll check.

[jpnovak]

A 902/1 is a 5 speed with AFMSX gears. Quite a fun box to have in the car.

This means you will need a 215mm flywheel and an early style (66-69) 215 mm clutch setup. Basically you need the early 6-bolt flywheel and clutch.

You will probably want to check that the output flanges on the tranny will mate with your CV axles. There were some year to year differences in flange diameter and mounting bolt patterns. If it was previously installed in the car this may not be an issue.

[Grady Clay]

The 4/66 is the date the main housing was cast, not the build date. This is consistent with a late ’66 or early ’67 911 or 912 (they went into both).

The 901.301.101. 0R is the casting number; not the part number or transmission number.

The Type 902/1 is a 5-speed geared AFMSX with a 7:31 R&P. It has a non-reinforced input shaft and a non-simplified differential (it has aluminum plugs in the centers of the axle flanges). This had a ‘push-type’ 215 mm clutch.

The transmission number 227935 doesn’t come up in my files. There is a series from 220001 to 221721. Could the digit you read as “7” possibly be a “1”?


I will add to the above recommendations to use a type 915 transmission. It will be year appropriate and much simpler. That said, there are 915s and there are 915s – lots of choices. If you choose this route, learn all the positive and negative features of all the different years (12 years total, 915/00 to 915/73 or such) and build yourself the best combination.

Matt, what would be the best combination?

Best,
Grady

[Tom C.]

The 902/1 is a five speed with slightly lower gears AFMSX (actually pretty nice stack of gears).

[Tom C.]

You guys are too quick for me

[RWebb]

I suspwct there will be trouble with the CV / drive flanges. IIRC, I had similar trouble with an early trans. mid-60's on my'73.5

If they don't mate then it is NOT worth the expense and trouble of machining adapters. Ins tead, you will want to get a later 901 box, or a type 911 (used in the 1970-71 MY cars, or go to a 915.

Don't forget the clutch cable and actuation for whatever you do.

I spent years on this stuff and haven't quite given up on a 911 box yet...

[EarlyPorsche]

You might not like the 5th gear on the highway in the 901 box. I am not terribly happy with mine but you could always install a higher top gear.

[Zeke]

Originally Posted by EarlyPorsche

You might not like the 5th gear on the highway in the 901 box. I am not terribly happy with mine

True dat, but you both could always sell those boxes to me. The weakness told here is mainly in 1st gear. Combine that with the 7:31, this is not a tranny for 250 HP. Who has 250 HP?? Only they have to be that worried.

[Matt Monson]

Originally Posted by Grady Clay

Matt, what would be the best combination?

Best,
Grady

The "best" combination (in such matters best is often an opinion and not a fact. ) would be a 915/43, as Rwebb suggests using. That will be a 7:31 with the removeable input shaft guide. The downside of that tranny these days is the cost. 7:31 R/P's have gotten pretty pricey for ones that are still good. There's lots of guys pushing junk as good and selling 7:31's that should be taken out of service because they are "rare". When shopping for one, be very very careful and if the price seems too good to be true, it probably is. So, if going with a 7:31 box, expect to pay or expect it to howl.

The cost effective solution is one of the 75-76 mag case boxes like a 915/44 with an 8:31 r/p. They still have the mechanical speedo drive and still have the course spline output flanges that one would be using on an early car like this. If you go any later you'll need to be mixing and matching parts onto a box (including changing the differential out, which requires resetting the ring and pinion set up) which starts to add up quickly.

Beyond that, you can ultimately make ANY 915 work but that may or may not be cost effective. Some of it depends on what you are willing to live with. You can probably find something like an aluminum 915/63 from an SC as a good used takeout for $800-1000 with known mileage from a reputible seller. Then buy a set of 930 output flanges for it (probably another $300-500) and you are in business. You won't have a working speedo, but your car will be on the road. It really depends on where this car is being taken with respect to use and long term plans for it and overall budget to "invest" in the car.

[DUBSMK2]

thanks for all the info i will be going with the 915