Early ring gear question

[mike95125]

Howdy,

I have a question about the numbers on the side of the ring gears on the 65-69 transmissions. There are two numbers on them correlating to some measurement, and the match number set. Example; 0.15 1234 -0.04

I am not sure how to interpret this, anyone able to enlighten me? 1970 and on, I got no issues as they changed things to make it easier.

[Jon B]

Originally Posted by mike95125

I have a question about the numbers on the side of the ring gears on the 65-69 transmissions.
There are two numbers on them correlating to some measurement, and the match number set. Example; 0.15 1234 -0.04
I am not sure how to interpret this, anyone able to enlighten me? 1970 and on, I got no issues as they changed things to make it easier.

For your examples:

0.15 (0,15) is the recommended ring gear backlash in millimeters.
-0.04 (-0,04) is the deviation from T-value in millimeters.

T-value is the blueprint dimension from the pinion axis to the back of the ring gear.
It was noted on the ring gear when tested by the manufacturer, but has no real use to the builder of a Porsche transmission after 1956.
It did have a use when Porsche & Volkswagen transmission housings were split lengthwise, and that dimension could be measured.

[Jon B]

Here is a reference to the pinion and ring gear numbers in the Porsche 911 Workshop Manual.
Volume I, page R42.

[mike95125]

We are really lucky to have such a wealth of knowledge as yourself and folks like Grady Clay. Thanks for answering my question. That was what I was interpreting the markings as, but could not find, in my library, the definite answer.
Thanks, man!

[Jon B]

Here is a better illustration of the T-value, or dimension, from an old Volkswagen manual.

T = blueprint value, pinion axis to back of ring gear.
t = deviation from blueprint value, determined in testing.

The 40,00mm "konstant" noted does not apply to a Porsche 911 ring & pinion.