901/13 gear question

Green 912 · 03-22-2002, 11:41 AM

Where can I find the gear sets in the early transmissions? I have a 901/13 in the car now (Mag case from an “S” or an “E”) I need to regear it for short track use. I know that 5th is ZA but I need the rest of the letters and I don’t want to pull it and open it up until I know and have the replacement sets.

Early_S_Man · 03-22-2002, 12:41 PM

Fifth gear wasn't ZA -- 29:22 until 1970 in the 911/00 and 911/01 transaxles! Your 901/13 had A, F, M, S, Z gears from the factory.

For gear sets ... check Andial, Stoddard, Powerhaus II, Guard Transmissions, and Pelican's wanted/used page. John Walker said he has some sets, too!

Check the chart John Walker posted in this thread:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=63247

TimT · 03-22-2002, 01:45 PM

a real good gear set for the 901 on a short trak is K-Q-V i think that gives like 125 mph@7200 rpm, besides the aformentioned suppliers of gears you can also get in touch with Gary Fairbanks

there are a few tricks you can use to keep from buying all new gear sets.

I know ZD become K when inverted, and Z becomes N when inverted, ZA falls between K&L. The S gear when inverted becomes a U, but if you use U for fifth that only gives you 110 mph top speed

get the 901 gear chart and play with the numbers, you may only need to buy one gear..

Green 912 · 03-22-2002, 06:40 PM

Thanks for the info! I have 3 units to swap out gear sets from so I hope not to have to buy any. I am just seeing what I have to work with in hand and the 901/13 is the one in the car. Someone else must have been the 901/13 before me as I removed a “ZA” 5th gear and replaced it with a “Y” before I put it in the car in a hurry for a track weekend. I then assumed that “ZA” was the stock 5th. The Y 5th is a little too tall as well. I bet the X will be 5th.

So far I have
A, F (2nd on the main), H, K/L (ZA flip), N (Z flip) M, O, Q, S, U, X, Y, Z, and the too tall ZA. I am running a 1720 CC 912 motor and my self-imposed red line is only 6500 but the valve train is good to 7000. Luckily, I have access to a nice gear-planning program so now that I know what I have in hand I think I will be able to plan and build up a good trans.

Thanks again to all for the help. Kurt

Early_S_Man · 03-22-2002, 06:55 PM

Here are a couple of charts that may help:

APKhaos · 03-22-2002, 07:31 PM

Warren strikes again.
Just when you think the question is imponderable, Warren posts the definitive answer with factory documentation [of course!].

Its guys like Warren that make this car obsession a real pleasure. Cant help but be impressed by the man, and look forward to the chance to buy him a beer or two. One day.....

Green 912 · 03-23-2002, 04:58 AM

OUTSTANDING! Tony K is spot on. My printer is chugging away as I type. Not only clear answers to my question but good info for future questions not asked yet.

Having access to the good folks on this BBS sure takes a lot of the headache out of owning and enjoying an early P car. A bargin at twice the price.

Thanks again.

pjv911 · pjv911's Garage

Whats a 902/05 box ? also a 902/07 ? Any info would be much apprieciated.

Kurt Williams

pjv911 · pjv911's Garage

bump for my last question

Early_S_Man · 05-18-2004, 07:49 PM

All of the '902' transaxles were originally designed for 912 model applications ...

Some were used in 911s, and some, but not all made it into the spec books ...

A search bogged down on me, multiple times, just now ... so try later on "902/05 trans*" ... I posted the ratios a few months back.

Clymer's Porsche 912 Handbook has some 902s listed.

blau911 · 07-10-2004, 02:21 PM

I took my 1967 911 to Europe last month and have been driving it on the Autobahn at fairly high speeds, but holding back from really letting it go in fear of overstreesing the engine.
I have a 67 911 normale with the original 901 gearbox. I rebuilt the engine to stock S spec's and kept the original gearbox which I assume had the same gearsets for the Normale and S models. Can anyone tell me what my max top end speed would be in 5th gear at 7200 rpm's? And can the car be left at this speed for an extended period of time (i.e. 20 minutes to an hour)? I have always heard that the early cars were overengineered and could handle red-line all day long. Being in Germany allows me the opportunity to test the car's top end.
Thanks.

ErVikingo · 07-10-2004, 06:17 PM

Hey Green,

I prepared an Excel spreadsheet with all the gears for 901 boxes which calculates the speeds at different RPM's using stuff I got from several different sources.

Email me if you want it:

ervikingo@hotmail.com

trak ratt · 12-07-2006, 06:08 PM

I like the “Porsche 911 Red Book 1965-1999” by Patrick C. Paternie, MBI publisher. Excellent pocket reference. Chapters grouped by model years, gives all the appropriate engine, trans, chassis number. Engine types, specs, plus year by updates and changes. Under $20.

pjv911 · pjv911's Garage

Quote:

Originally posted by david riley
I like the “Porsche 911 Red Book 1965-1999” by Patrick C. Paternie, MBI publisher. Excellent pocket reference. Chapters grouped by model years, gives all the appropriate engine, trans, chassis number. Engine types, specs, plus year by updates and changes. Under $20.

Excellent book but it does not cover the 912 cars or the 902 transaxle. Everyone on this board should have that book.

Kurt Williams

84toy · 12-07-2006, 09:21 PM

Warren, Great charts!!! Thanks for posting them

By any chance do have similar for the 915? I would love to be able to look at a tranny # and know what was in it....

joetiii · joetiii's Garage

Quote:

Originally posted by ErVikingo
Hey Green,

I prepared an Excel spreadsheet with all the gears for 901 boxes which calculates the speeds at different RPM's using stuff I got from several different sources.

Email me if you want it:

ervikingo@hotmail.com

Juan,

emailed you for the spreadsheet.

My question to all regarding the 7.31 ring&pinion. I read that this gear is a weak link when installed in the 915 gearbox. I assume it is no different than the gearset in a 901. How much crank torque and horsepower can it handle?

Grady Clay · 12-27-2006, 09:32 AM

Joe,

The 7:31 R&P is the only choice for a 901. The only other ratio available is the 6:29 from a ’69 912 and is not strong enough for a 911 (it was a “use once” choice for the 910 hillclimb car). The R&P from 905 Sportomatic are not interchangeable to 901.

Only the 915 has the choice of the 8:31 or 7:31 (this 915 7:31 is not interchangeable with the 901 7:31). The 8:31 is preferable for strength.

Best,
Grady