Gearbox oil leaks

[packers1712]

Just a note on the above, I have been slowly re-commissioning my Amazon and some of that has involved attempting to cure oil leaks, engine and gearbox.
Whilst looking for the gearbox leak I discovered that the casing that houses the reverse light switch wasn't tight so I obviously tightened it and continued to decide which casket the oil was coming from (M41 with O/D), cleaned everything down, went for another road test and upon returning home clambered back underneath to try and find the source only to find virtually no leaks at all (tiniest amount from the prop output lip seal).
I'm thinking that the majority of my leak was being caused by the loose machine screw holding the housing in place, is this possible? Is the thread in the main-case a through hole?
If so just thought it was worth sharing with the forum users.

Doug.

[powen1]

Originally Posted by packers1712

Just a note on the above, I have been slowly re-commissioning my Amazon and some of that has involved attempting to cure oil leaks, engine and gearbox.
Whilst looking for the gearbox leak I discovered that the casing that houses the reverse light switch wasn't tight so I obviously tightened it and continued to decide which casket the oil was coming from (M41 with O/D), cleaned everything down, went for another road test and upon returning home clambered back underneath to try and find the source only to find virtually no leaks at all (tiniest amount from the prop output lip seal).
I'm thinking that the majority of my leak was being caused by the loose machine screw holding the housing in place, is this possible? Is the thread in the main-case a through hole?
If so just thought it was worth sharing with the forum users.

Doug.

Hi Doug, its always good unto go out after fixing a part and seeing its dry ! :-) I don't think the bolts are through, but I thought yours leaked from the side on the Gasket with lose bolts?
I had my M41 gearbox rebuilt re fitted started leaking :-( after investigation found the front cone to be incorrect and return oil drain didn't line up , but that's been sorted and seems ok now.
I also found missing bolts in the bell housing - most annoying from previous owner
Always Something to do !
Cheers Paul

[packers1712]

No the cause of the leak that I shared with you on text, the gasket not being installed correctly, was an engine oil leak and at that point i didn't even know I had a gearbox leak I thought all the oil was from the engine!

Doug.

[jimbo1593]

I have an OD leak from the rev counter drive. The rest is bone dry.

[Derek UK]

Check and tighten ALL of the bolts after you have cleaned all of it down.
Speedo cable not rev counter. A common leak spot. New seals easy to fit.

Don't forget to check the gearbox oil level.

[142 Guy]

I don't recall the retaining screws for the reverse light switch cover being through-the-case. However, the through the case hole that the shifter rail pops through is not exactly a precision fit and allows oil to weep through and eventually out around the cover edge. The gasket between the back of the transmission face and the OD adapter piece extends up into the area around the reverse light switch. The edge of switch cover presses on this gasket to form a nominal seal. If the gasket is old that seal is pretty ineffective. Even after I regasketed my M41 that area around the reverse light switch developed a nice layer of oil / dust pretty quickly.

For jimbo1593, the speedometer drive has two rubber seals on it. 380192 and 191117 for the M41. Replacing those seals should eliminate the oil leak.

[packers1712]

Well my car definitely doesn’t have an extension on the gasket that is between the main case and overdrive to capture the cap that retains the reverse light switch, that cap/casing is just butted up to the back of the main case where the selector rods protrude out! Perhaps the reason why my cars gearbox leaks?

Doug.

[142 Guy]

This is the correct gasket for the back of the transmission.

https://www.cvi-automotive.se/en/art...30m40?q=380800

They are normally part of the M40 / M41 transmission gasket set, not the OD set. As noted, even when new they are not spectacularly effective. If you still have a leak after tightening the cover and want to address the problem, I suggest that after removing the switch cover, try to clean the mating area of oil with a fast evaporating solvent such a acetone and then use a bead of sealant such a hylomar blue on the edge of the switch cover to seal it to the back of the gearbox.

[simonvolvo]

Yes, small amounts of gearbox oil do leave the gearbox casing where the selector rods pass through. But, if you look very carefully (when the aluminium cover has been taken off), you will see a tiny drain hole in the wall of the casing through which this oil is supposed to return to the inside of the casing.

Sometimes the gasket interferes with this return flow or partly dams it up. This aggravates the problem, where the seal between the edge of the cover and the casing is not so good to begin with.

[c1800]

Not at my car now, but there are 2 top bolts that mate the OD to transmission? that require copper sealing washers. When I checked, one had a mangled copper washer and the other one had a split ring lock washer. I replaced both with new copper washers and the somewhat voluminous leak stopped. Sorry I can’t be more specific.