M41 gearbox breather
 

Good evening all,

Can anyone tell me where the gearbox breather is on an M41 box with a J type overdrive unit is please, mine is leaking oil and I want to check the breather before I dive into replacing seals and gaskets? Pictures would help!

Doug.

Hi Doug I seem to remember a copper top somewhere between gearbox and O/D unit if you can see it - have you tried cleaning the oil off and then see where its coming from or if you can post a pic may help
Cheers
Paul

Are you sure that there is a dedicated breather? When I re gasketed my M41, I don't recall anything that looked like the dedicated breather tube that the differential has. I would think that the slightly loose hole that the selector rod pokes through on the back of the transmission to activate the reverse light switch would suffice to control pressure build up in the transmission and OD.

If your reverse light contact is original, give consideration to replacing it while the transmission is out of the car as a bit of preventative maintenance. On the M41, the presence of the OD makes getting at the reverse light contact to replace it a real treat if it fails.

According to the Haynes manual there is a “breather” directly above the base plate where the filter lives on the left hand side off the gearbox but mine doesn’t have anything there! It’s difficult to decide where the oil is coming from I’ll just live with it for now it can be on next winters re-prep list I definitely can’t be bothered to pull the box out again now! I’ve done the reverse light switch in situ it is a bit fiddly isn’t it!

Doug.

I don't recall ever seeing a vent on a M40/41 and 142 Guy is probably correct about it venting thru the shifter rod. However, I'm rebuilding a 1970 1800E 410 gearbox which has a dedicated vent on an electrical switch which I believe is the reverse light switch on the back of the box. It is a small hole with a u-shaped a tube coming out of it.

Ah! Mystery solved. 'Directly above the base plate where the filter lives' indicates that they are referring to the OD unit, not the gear box proper.

If you download the Volvo OD manual and look at the exploded diagram at the end of the manual you will see it marked as part #5. If it exists it should be above the normal oil level and threaded down into the body of the OD, so probably closer to the top of the OD.
https://volvo1800pictures.com/docume...20shooting.pdf

I have a 1971 142. When I re gasketed my M41, I do not recall seeing the breather and my 1971 Volvo service manual does not show it. However, my Haynes 140 service manual (which covers all years) does show it so perhaps the breather got deleted on later versions of the OD.