More gear box number and type questions

At the risk of turning into one of those new members who only seem to ask questions about one subject, I have another question about my gear box number. I have every reason to believe it and the motor are original to the car, the engine number and model number fall into the right range, but the gear box number has been ground off over time. I'd like to confirm from PCNA that they are indeed the originals, but evidently now you pretty much have to give them the numbers and they confirm it.

The box is out of the car, and the techs at Steinel's here in Ohio are pretty comfortable thinking that the almost illegible gearbox number's last digits are 8064. This is reasonable considering the serial number range and it being a 1973.5 911T with a fairly late (estimated) build date. But the first few digits are unreadable.

So my question is, does the casting number on the box give any clues to the model number? Tech Specifications lead me to believe it's either a 915/02 or 03. The difference is "shaved" versus ground gears, which I don't understand. The casting number on the gear box is 915301102 OR.

Thanks in advance to all for your answers.

Bill S.

Hi Bill the case casting number wont help you as it is what is inside the case that is important.
However I think you have the important numbers already and maybe can bluff your way through with Porsche
those last 4 numbers (8064) are the unique serial number of the box

there are 7 numbers on a 73 915 box the first is 7 (for a 6 cylinder car) that is a given
the second is a transmission type I take it that it is a manual not a sporto so that cuts it down
as a 73 T is is most likely a 3 (5 speed 915/02) but you would know if it is a 2 (4 speed)

the third number is easy - the model year - in your case a 3 so that is a given and really there is only one number to guess and knowing whether it is a 4 or 5 speed or sporto cuts down the odds

So If you have a 5 speed i would guess and say it was 7338064

I have a lot of records of these and from my records I would be guessing that your car would be up in the 911 310 2400 range to have a gearbox with a serial number 8064 Is it around there ? If so it would be a good bet to sumnit that number

Hugh, your knowledge and guess is nothing short of astonishing!

The chassis number is 911 310 2388!!!!!

That's good enough for me. I'll be sending my info and money off to PCNA next week.

Thanks again and best wishes, Bill

Oh and btw it is indeed a 5 speed.

Bill S

for reference 9113102385 has engine 6134461 and transmission 7338063

Shaving is the most widely used method of finishing gear teeth used in automotive gearboxes. It provides the best cost/performance ratio due to the production rate of a shaving machine being much higher than that of a grinding one. The main limit of the shaving process is the difficulty of precisely controlling deformations caused by heat treatment, an operation that is performed after shaving. In cases where this method cannot ensure a finished gear of sufficient quality, different processes are used, like grinding after heat treatment. Ground gears often have advantages in terms of noise control. So transmissions with shaved gears were a lower cost alternative.

Thanks Dave. My engine is 6134454. Looks like that car-yours?-rolled out the same day.

I'm very pleased, very likely original it seems. And an original Ohio car with all original panels as well except for the trunk lid!

Hugh may not appreciate that, basking comfortably in Melbourne, but I bet you do, as a fellow resident of this wintry, salty end of North America.

Thanks again to both of you for your valuable and helpful responses.

Bill S

No, not mine, but in my database. See my edit of my post for info on the shaved gears.

As a side note about gears, shaved and ground.

Dave, thank you for the edit on shaving. I've now obtained my own copy of the Technical Specifications book as opposed to looking over someone's shoulder at their copy, and the gear box section prominently references "shaved" and "ground" gears for the various transmission models. I have a lathe and mill and have cut one simple set of gears, a procedure which takes a fairly significant amount of math and time on a mill. I was familiar with the concept of grinding gears, and I assumed "shaving"
was a process of manufacturing them on a specific type of machine in an industrial setting, using something like a Gleason gear generating machine, which I have read about but am not familiar with. Your explanation was extremely helpful and descriptive, and saved me from asking my next question, which was of course on the shaving process!
Regards, Bill

And thanks to Gled for his picture, which shows the finer finished ground gear with its radial reflections on the right.
Bill S