Manual gearbox pressurising

[Steve B]

I'm working my way round sorting out all the leaks and need some help with this one. I've just changed the clutch so the gearbox is nice and clean to see where the oil is coming from. I replaced the speedo seal and that's now okay, and I changed the J type rectangular seal at the bottom of the gearbox at the weekend and the oil is still coming from the new gasket. I did use a smear of Hylomar Blue on both faces. I'm reluctant to over tighten the bolts in case of stripping the threads.

I spoke to someone yesterday who said that the gearbox is pressurising and the oil is being forced out of through the weakest point which is this seal. I know there is a vent on the very top of the gearbox. Is there any way of getting to it with the engine and gearbox fitted? Has anyone got any thoughts and solutions please? It's embarrassing parking on drives as we are not talking about small drops here.

[Phil S]

Not to worry...the oil will soon run out....not a lot of help am l!
Phil

[sujitroy]

The OD needs the pressure to operate not the gearbox. I'm working on a rebuilding a manual gearbox with J type OD and i am not aware of any vent. Get a torque wrench and tighten the bolts.
Taken from the following website

http://www.buckeyetriumphs.org/technical/jod/JOD3/JOD3.htm

Sump: Both sides of the sump gasket were coated with Hylomar sealer and the sump cover was then installed. See photos below. The six bolts were tightened to 6 lbf ft (72 lbf in). (I don't know the origin of the rust colored stain on the bottom of the sump cover --- maybe rusty water had laid in it for a while.)

Sujit

[marshman]

Steve, not sure it will be of much help but if you don't already know the exact location of the breather hole it is shown in this technical reprint, next to one of the bolts at the front end of the remote extension. You may be able to access it with a long piece of stiff wire - steel welding rod? - threaded down between the bell housing and bulk head - you may need a good light and some well positioned mirrors to guide you. or if your car has the access plate in the side of the transmission tunnel used to access the inhibitor switch on the BW35 this may get you closer. Mines an auto so can't help beyond those ideas.

http://www.stag.org.uk/technical/page0104.htm

Roger

[flying farmer]

Can't say I have ever had a problem with leaks from this gasket on multiple J type overdrives over the past 30 years.

The fact it was leaking before makes me wonder if there is a problem with the cover, I wonder if it is distorted from a previous gasket replacement?

I have not ever tried reaching the breather hole with the box installed so have no idea if it is possible.

Neil

[Bandit1200]

If the breather at the top of the gearbox is blocked then the heat generated in the gearbox under normal operation will pressurize the box and blow oil out of the weakest joints.
The pressure required, referred to by Sujitroy, is oil pressure and not pressure within the box housing. Two completely different things.
If you follow the suggestion by Marshman to unblock the small breather hole at the top of the gearbox housing you will have done well. Otherwise you will need to drop the box to clear the breather hole.
I know this from personal experience.
Best wishes
Steve

[sujitroy]

Thanks for the correction. I'll check this breather.
Sujit

[Steve B]

I thought I had cleared the top vent when the gearbox was out for the clutch and yes I do know where it is. It was blocked with what looked like the black insulation padding from the gearbox tunnel. Stuff came out but obviously not sufficient. I've just got another gasket but I also have a spare J type O/D in the loft. I'll change the bottom covers over and see what happens on the drive up to the National. Another thought as the top vent is inaccessible in the car, is to modify the filler plug. I'm thinking of drilling and brazing a tube through the plug so I can attach a plastic pipe and take this up higher in the engine bay. Any oil forced out under pressure could be collected here and not left on the ground.

I've changed all my filler and drain plugs to the ones that have a magnet so this type will be easy to modify. Automatic Stags have a filler/ dip stick tube in the engine bay. Thoughts anyone?? At the minute I've got a cat litter tray as one of the friends we are staying with has new block paving they've just had fitted….

[sujitroy]

Here's photo of the breathe in the top gearbox cover. I just ran a pipe cleaner through it and then ran some oil through it from the other side. All clean. Fortunately, my box is sitting on my work bench. Very unlikely you'll get to it with it in the car.
Sujit

[Lingen]

Steve.
A blocked breather will certainly encourage leaks. I had the box off to sort out a clutch problem, so took the opportunity to change all the gaskets and clean the breather, which was blocked. Then I remembered the 'O' rings on the selector shafts, which were a real pain to replace, but I am pretty certain that they were the major cause of the mess under the car.
Mike.