901 vs 915 gearbox

dd74 · 09-15-2003, 10:39 PM

I'm thinking of swapping a 901 transmission in place of my 915, and have a few questions for the board.

1) Is this possible?

2) Will the 901 withstand the torque of my 3.0?

3) Is it lighter than a 915?

4) Can the 901 be used with my Sachs Sports clutch?

5) Because I have a 915 with a 7.31 ring and pinion, will the gearing in a 901 be "less sporting" or "more sporting" than what I have now?

Thanks all...

Supergranule · 09-15-2003, 10:42 PM

why are you wanting to do this swap?

dd74 · 09-15-2003, 10:44 PM

Quote:

Originally posted by Supergranule
why are you wanting to do this swap?

Weight savings. And general curiosity. Do you know anything about a swap like this?

Early_S_Man · 09-15-2003, 11:37 PM

dd,

The weight savings would be 20 lbs. It wouldn't be my recommendation to lose the weight that way! Fiberglass rear bumper would be a greater weight savings!

The only practical swap would be the '70 - '71 '911' version ... in order to use your existing flywheel, but the clutch cable routing and throwout bearing operating mechanism is the most diabolical ever devised by man! The clutch disk will have to be for the '71 to fit the VW-size input shaft ... pilot bearing won't match input shaft, so input shaft may have to be sleeved.

Gearing could be very similar to your 915 ... both share the 7:31, ring & pinion. Here are some pertinent charts:

Randy Webb · 09-16-2003, 12:17 PM

The 901 has a better road driving shift pattern and is lighter. You will need to avoid any drag race type starts, and will not enjoy driving in stop&go traffic due to the 1-2 shift. Kennedy and Patrick both make adapters for any 901. At one point in time the 901 changed from Al to Mg (or was it from Mg to Al?) in part of the case. Somebody makes a strengthened part for part of the 901, but I'm not sure which part or who. Also, you will need to modify your carrier as shown on a thread on Early 911S forum.

Yes, you can do it. There are 2 advs. on open roads. And you will need some aftermarket parts.

CamB · CamB's Garage

Look at those "Hillclimb" ratios! That "O" top gear is slightly shorter than an SC's 3rd (allowing for different R&P).

I calculate it would mean about 103mph at 8000rpm...

dd74 · 09-16-2003, 03:14 PM

Cam - which gearbox are you referring to?

CamB · CamB's Garage

901/51 or 901/81

Assuming 8000rpm (anything less would not really be realistic) it looks like this (with a 185/70R15 tyre):

(did I get this right??)

Zeke · 09-16-2003, 05:02 PM

Quote:

Originally posted by Randy Webb
Somebody makes a strengthened part for part of the 901, but I'm not sure which part or who.

I think you are referring to the billet intermediate plate. I'm sure Patrick and Otto's have it amoungst others.

Randy Webb · 09-16-2003, 05:29 PM

"billet intermediate plate

- Yes, that's it -- thx.

gregk1 · 09-17-2003, 06:31 AM

I have a 901/02 LSD in my 66 and I go down the freeway at 70 mph and turning around 4000 rpm with I think 205/60/15 tires

Joe Bob · Joe Bob's Garage

I had a 901 in my 3.0 powered 914/6......The first gear is weak and finally gave up the ghost on continuous burn outs....sure was fun though. Cheaper to rebuild than a 915 but on a tail dragger like the 911, the engine has to come out to get to the box.....

Diferent shift pattern, PITA on the 1st to 2nd upshift. Forget about the 2nd to 1st downshift if moving mre than 5mph.....

Stay with the 915....or go to the G50 if you want a better ****ing box....