915 gearbox shiftrod seal

[Doc Martin]

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

[Doc Martin]

Here is a picture of my "squeezer" tool, used to compress the mastic seal.

[Daugaard]

The steel surrounding where the shiftrod go in the gearbox are part of the seal, you have to remove this before you put in the new seal. there are only alloy where the seal go in.

[porschyard]

Are you sure you don't have a G 50 trans ? The old seal you show in your picture is for a 1987 or later G 50 series trans,
carrera 3.2, 964, 993

[porschyard]

Heres a pic of the 2 different seals, the one on the left is for a G 50, dimensions are 16x24x7.5
The smaller seal on the right is for 915, dimensions are 15x24x7
Also i would advise to polish that shaft a little better as its looking pretty rough.

[porschyard]

Can you post a pic of the trans, would help ID the trans

[Flat6pac]

The coupler is a 915. The G50 has a very short selector shaft.
Bruce

[Doc Martin]

I have included pictures of the gearbox serial number, and also a couple of pictures of the gearbox (the only ones I have, as I am not at home at the moment to take more). (The old gearbox mounts have been replaced since the pictures were taken.)

The evidence available to me is rather puzzling. As far as I know, I have a 915 gearbox, because -
1. The serial number states "915".
2. The shiftrod coupler is for a 915.
3. The shiftrod diameter is precisely 15mm (measure with vernier calipers).

However, comparing the picture of the G50 seal provided by "porschyard" with the one in my original picture, the seal I removed appears to be that for a G50 (though there was no evidence of the metal spring shown in the picture, and as I explained above, it came out in fragments).
I note that the G50 seal is 16mm I/D and my shiftrod shaft is 15mm (my old seal was seeping oil).
I did wonder whether a G50 shiftrod housing had been fitted to a 915 box, but I doubt this is possible, and the fact remains that I have a 915 coupler and a 15mm shiftrod (I assume that the G50 shiftrod is 16mm diameter, the seal I/D being 16mm).

(Incidentally, the shiftrod does appear to be a bit marked, but I have polished it with fine grade emery paper and there are no burrs. The gearbox is currently set in 1st gear, so it is at its furthest selection position within the gearbox i.e. the part of the rod you see will not engage the seal when fitted).

As it happens, having driven the vehicle, my temporary seal seems to be working just fine with no seepage at all, so the job is not urgent. However, I would certainly like to find an explanation for this puzzle and thus fit the correct seal.

[Doc Martin]

Forgot to mention, the engine number is 6304510 (6 cyl, type 3, 1980, serial 4510).
I have also been told by my local 911 specialist that it is a 915 gearbox.
(If anyone is interested, there are pictures of my vehicle in my "garage" link.)

Thanks,

Martin Birch

[john walker's workshop]

So use a 915 seal. What other choice is there?

[Doc Martin]

Agreed. No other choice. However -
1.
It looks like the seal that came out was for a G50 (comparing my old one with the picture provided by "porschyard").
I suppose it's possible that the previous owner fitted a G50 seal (24mm O/D, 16mm I/D) instead of a 915 seal (24mm O/D, 15mm I/D), which would explain why it was seeping oil (the shiftrod being 15mm in my 915).
2.
I can't get the 915 seal to fit (either by drifting, or using my squeezer gizmo).
Though it's a bit approximate (the shiftrod being in the way), my verniers give the housing I/D as 22.5mm, which is too tight to fit a 24mm seal.
I've cleaned the inside surface of the housing with fine emery paper and there appears to be no residue remaining.

It's all very puzzling, so I'll continue using my gland packing solution for the time being and see how it goes. It's certainly better than it was with the old seal. So far so good!

[porschyard]

Yes definately a 915 with a G50 shift rod seal.
Did you remove the steel flange left over from the G50 seal, it sounds like you are trying to install the new seal into whats left of the old seal.

[Doc Martin]

Thanks. I'll check that out and report back. (Might be a few weeks.)

[MBEngineering]

HI Doc Martin

the selector shaft hole should be 24mm , you will have to check there is no part of the G50 seal left in the end case,

the shaft needs a good clean before fitting, also check the hole for the coupling pin, that it has not damged the shaft, as this will damage the seal when fitting

check the inside of the end case before fitting the seal, as the edge some times will pull the outside of the seal off if fitted dry,

I usualy run a bearing scraper round the start of the hole to get the seal in in one piece, there again I do have the seal fitting tool for the seal when the end case if off to get it in square

the other thing that may need checking, is the shaft bent, I usualy find that the shaft gets bent when the engine/box is not removed carefully, with the shaft getting bent in the through hole in the rear baulkhead of the 911

the gear box should be a 915/62 with it beeing a 1980 engine?box