I am replacing the shiftrod seal in a 915 gearbox (no. 915/6? 730 4799, not sure what the "/6?" is about, but I think I understand the rest of the number). The engine is a 1980 3.0 SC installed in a VW T2 camper, but the gearshift is very precise nonetheless. The old seal was seeping oil, and on inspection it appeared to be non-standard, as the attached picture shows.
This was confirmed when I removed it with some oil-seal picks - there was no solid metal body or "spring" within the seal, and it fragmented so had to be removed in bits. I then cleaned the inner surface of the housing with fine emery paper. I also noticed that, unlike other gearboxes I have seen on the web, there is a 3mm flange on the outer surface of the housing (see above picture - the black gizmo in the foreground is my home-made coupling boot, before removal).
I obtained a 915 replacement seal from Design911 in the UK (picture attached), on which were the following dimension marks in mm: 24 (O/D), 15 (I/D), 7 (thickness).
I attempted to hammer the seal into the housing with a "drift", but the line was bad, and I was working under the vehicle (jacked-up on axle stands), so this proved unsuccessful. In fact, the seal was very slack on the shiftrod and easily slid down by hand until it reached the housing. I then decided to take advantage of the flange and made a squeezer tool to slowly wind the seal into the seat (it was a steel plate, with four "claws" made from M6 studding to grip behind the flange). However, this also failed because the flange was not robust enough and started to distort, with the seal refusing to even begin to enter the housing.
Though the seal was definitely for a 915 box, I checked the dimensions with a vernier caliper and found that the shiftrod is 15mm, which is the same diamter as the seal I/D, which surprised me (though this explained why it hardly gripped the rod at all). I also found that the I/D of the housing is about 22.5mm (I say "about" because it is difficult to be precise with the rod in place), and this seemed much too tight for a 24mm seal with a metal sub-structure. So the "correct" seal for my gearbox is too slack on the rod and too tight in the housing!
I am now pondering what to do next. In fact, I have used a temporary marine solution and have packed the housing with some non-setting fibrous mastic, made tight with my "squeezer" tool, and this seems to be completely leak-free when the bus is driven. (It uses the same principle as a propeller shaft gland in a boat.) So at least I will be able to drive the bus to my local Porsche expert. Indeed, I suspect that my temporary fix might prove permanent!
Nonetheless, I would appreciate any comments and advice on my problem, as it seems to be non-standard, and yet the gearbox is definitely a 915.
Thanks.
Doc Martin
Preston
UK.
mjbirch@uclan.ac.uk
