Missing Transmission Number on a 915

trconway · 10-29-2007, 12:37 PM

I finally started cleaning my engine/transmssion and in looking for a transmission number I find that the raised ridge where the stamped number is located has been broken/ground down. My first question is does a missing number present any problems in and of itself?

My second question is about the mounting point for a spring:

The small spring in the center of the photo is the one in question. The bottom mounting point is missing on my case.

BTW I copied this photo from the article here on Pelican about replacing the clutch helper spring. Thank you Wayne.

Tom

trconway · 10-30-2007, 04:31 PM

Hey can anyone assist me with this?

Thanks.

Tom

TRE Cup · TRE Cup's Garage

by bottom point, are you referring the the post that is cast on the number base? If that is missing, you can fabricate a bracket , drill thru the rectangular section, and pass thru bolts to secure your bracket. This can be done without disassembly of the trans or welding on it

trconway · 10-30-2007, 05:16 PM

TRE Cup, yes that is what I'm talking about. Sounds like this is not that unusual. I'm glad there is a fix for it.

Thanks.

Tom

Geary · 10-31-2007, 10:09 AM

Regarding the first part of your question: Ground-off serial numbers are usually associated with "hot" transmissions. A staggering percentage of used Porsche transmissions floating around fall in this category. This is why you always want an invoice clearly stating the serial number on any used engine/transmission that you purchase.

In California, the ATF "drops in" on establishments specializing in used high-end parts for the purpose of spot-checks. Unfortunately, it can take a year or more for ATF lists to be updated, so they could come back a year later to confiscate an item. You can imagine the tangled web, especially if the unit has been sold/rebuilt/upgraded. I have heard absolute horror stories ...

trconway · 11-01-2007, 09:21 AM

Yeah that did cross my mind but nothing to do about it now.

Thanks.

Tom

pwd72s · 11-01-2007, 10:26 AM

Quote:

Originally Posted by Geary

Regarding the first part of your question: Ground-off serial numbers are usually associated with "hot" transmissions. A staggering percentage of used Porsche transmissions floating around fall in this category. This is why you always want an invoice clearly stating the serial number on any used engine/transmission that you purchase.

In California, the ATF "drops in" on establishments specializing in used high-end parts for the purpose of spot-checks. Unfortunately, it can take a year or more for ATF lists to be updated, so they could come back a year later to confiscate an item. You can imagine the tangled web, especially if the unit has been sold/rebuilt/upgraded. I have heard absolute horror stories ...

Hope Evren doesn't run into any trouble over this. Some of the numbers on my old car's transmission have been ground off....courtesy of a #!%! too high speed bump @ a Linn County, Oregon park!

Bobboloo · Bobboloo's Garage

Probably the majority of 915's out there don't have their serial numbers anymore. Porsche unwittingly put the serial numbers at the lowest point on the 915 tranny. They've been erased by many a speed bump or driveway. I wouldn't worry about it.

Geary · 11-01-2007, 11:29 AM

Possibly so.... but you can tell. I'm gun shy since being sold two 930 trannies that were obviously of dubious origin, by a well-known used parts peddler. It took me months to get a refund .... and then another shop happily purchased them. In asking around, I got the amazing statistics of loose, undocumented transmissions ....

Grady Clay · 11-01-2007, 01:10 PM

Bobby is right on.

This is one of the few simple issues that Porsche did that doesn’t pass the engineering laugh test. No offence intended as they did so much else well.

Porsche had historically put the transmission serial number and type numbers stamped in the rib just behind and below the differential area. This was reasonably well protected from pavement abuse. I think this was true from the pre-war VW era.

For the ’71 model (and it may be true from late ’70 models, but just pre-July ’71), the later version of the Type 911/01 and variants had a nice boss cast under the differential area for the serial number and type number. This was very well protected from road abuse. This was the last use of the type 901/911 but continued through ’76 with the different) 914. Some ’71 914-6s had the later 911 casting.

Starting with the ’72 915, Porsche forgot everything they learned and put the transmission number, transmission type and LSD designation on the clutch cable support under the differential. This is the LOWEST point on the transmission and 99% of the numbers have been ‘scraped off’ by contact with the pavement. It was such a poor design that the clutch cable support broke off, fixed with a separate part.

No one is laughing now because it is very difficult to determine the actual type number of a 915 without dissemble and impossible to recover the transmission number without very expensive forensic attempts.

The good news is you can tell all the important ‘facts’ only with simple inspection and disassembly of the transmission. Nothing you wouldn’t do in a normal service and repair.

If anyone is concerned about their transmission sequential number (7TypeYearxxxx), LSD indicator number (12) and transmission type number (915/xx), get your CoA from PCNA and make it correct.

Same issues with a 930.

Your local State Police might be convinced to apply their forensic magic. Our ever diligent FBI is too buisy chasing phantom spooks to bother with lowly Porsches (told this first-hand several times recently).

Best,
Grady