Transmission number scraped off?

blue72s · 04-19-2011, 12:41 PM

I looked under an early 911 today and tried to look for its gearbox serial number (mag 915) but apparently it has been scraped off, so I'm wondering whether that's common (due to kerbing or gravel?) or unusual?

How many scraped off gearbox numbers have you seen?

Peter Zimmermann · 04-19-2011, 01:13 PM

I think about 3-5% of transmissions that I've had on my stand have been damaged to the point where the number, or the type "915/xx" is not legible.

trconway · 04-20-2011, 07:05 AM

I have this same issue with my 915. What visible cues can I look for to get more information about my 915?

Thanks.

Tom

Peter Zimmermann · 04-20-2011, 07:35 AM

Tom; For magnesium case units... If your trans has a cable-drive speedo it will be a 1972-75 unit. If your clutch cable connects, at the trans, in a straight line, it's a 1972-74 unit; the '75 has a peculiar right angle turn a few inches from its end.

If you have an electronic speedo, and a straight clutch cable, that's the easy one - it's a '76 unit. If you have a hook-type end on your clutch cable, and a complex looking spring arrangement where it connects, you have an early '77. Beginning in mid-year '77 transmission housings were made from aluminum and were built with the same clutch cable set up (used at the beginning of '77) through 1986.

All '76 and later units have an electronic speedo connection, all '75 and earlier units use a mechanical speedo drive.

If the bell housing is visible, differences exist with the throw out bearing guide tubes in the different models.

trconway · 04-20-2011, 08:04 AM

I got the 3.0 l engine and trans from a donor car. Along with the trans number the spring attachment post was gone. Assuming I had the correct trans/engine combination, a hole was drilled for the spring to attach to.

Tim K · 04-20-2011, 09:25 AM

Wow Peter. That's a great breakdown.

Thanks,

Tim K

blue72s · 04-20-2011, 10:12 AM

3-5% is rare. But what are the main causes of the numbers getting scraped off?

The previous owner of the car I looked at lived in a mountainous countryside and the drive up to his house was very rocky and muddy - no tarmac, so I guess that's what caused it.

Peter Zimmermann · 04-20-2011, 12:05 PM

Quote:

Originally Posted by blue72s

3-5% is rare. But what are the main causes of the numbers getting scraped off?

The previous owner of the car I looked at lived in a mountainous countryside and the drive up to his house was very rocky and muddy - no tarmac, so I guess that's what caused it.

I don't always see the cars that I do transmissions for, but I have a hunch that the combination of ride height (Euro or lower) and a steep or angled entry to a driveway can certainly contribute. Of course, this is just a guess; I've never scraped the bottom of my own car, and it's set at Euro height.