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Educate me on R&P

I need some 'exposure' to R&P configurations.

I have numerous cars and tranny and would like to know:

1. R&P on an '83 SC. (on the car)
2. on a '77 911S. (on the car)
3. 197x 915 magnesium tranny.
3. 86 930 tranny.
4. Factory short-bellhousing 930 aluminum tranny (197x).

Do R&P numbers affect the 'speed/signal' sent to the speedometer?

Is R&P same as 'gearing?' (tall/short)?

(stupid question: R&P cannot be known unless you take the tranny apart, right?)



p.s.,

Can I decipher the 'year of make' based on serial numbers? How?

Old 01-05-2004, 07:52 PM
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From what I've read r&p on stock 915 diffs is 7:31 thru 73, then 8:31 for all later 915's.
Old 01-05-2004, 08:53 PM
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this might help:
Best gearing for 915/3.6
Old 01-05-2004, 08:58 PM
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1. R&P on an '83 SC. (on the car)
8:31

2. on a '77 911S. (on the car)
8:31

3. 197x 915 magnesium tranny.
for sure 1972/73 7:31 not sure after that

3. 86 930 tranny.
unsure

4. Factory short-bellhousing 930 aluminum tranny (197x).
unsure

Do R&P numbers affect the 'speed/signal' sent to the speedometer?
where there is a magnetic pick up, no, where there is a mechanical pick up, yes, but only 7:31 were mechanical I think, so should not effect the system

Is R&P same as 'gearing?' (tall/short)?
Yes and no, R&P effect the final drive, so a tall set of gears that would be good for highway crusing with a 8:31 would not be considered tall with a 7:31, Tall gears for a 7:31 would be too tall for a 8:31

Jim
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Old 01-05-2004, 09:00 PM
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You need both the 'Type Number' and serial numbers off the bottom rib of the 915 to do the decoding. Type Number is always in the form 915/xx ... and the serial number includes the production year in the sequence.

Sometimes, however, one or more digits have been scraped badly or obliterated by road damage.
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Old 01-05-2004, 09:49 PM
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One bit of additional info - I think the 7:31s were used in the 1974 model year 915s also.

Mike
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Old 01-06-2004, 04:19 AM
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Yes, the 7:31 was used in all 1974 models, the 1976 912E, and all ROW Carrera 2.7s thru the last 123 made in late 1975 as 1976 models, as well as the entire small run of Carrera RS 3.0s.

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Old 01-06-2004, 06:34 AM
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