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Malcolm Clarke

Gearbox breather hole

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About to try and attempt to trace the cause gearbox oil leaks. Question: Should there definately be a breather hole in the gearbox top cover. Seem to  remember reading somewhere that a breather was not necessarily included if the box was mated to an A type overdrive (which has a breather on the casing)

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Hi Malcolm,

you may well have to make your own hole. It is just to relieve pressure caused by heating.

1/8" will do it - fit a small split pin to ehlp keep the hole open.

Forward left hand corner is popular

The two arrows in the pic show the original breather to the left and the added hole to the right

However there is a very good chance it will still leak

Roger

P1050269b.jpg

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In the original gearbox design there is a hole about 1mm diameter located in the front of the selector cover. It's easily blocked and I can see why Roger drilled a larger hole and fitted a split pin.

Where does your gearbox leak? Overpressure due to poor venting can cause a leak but often it's something else- generally seals.

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9 minutes ago, Mike C said:

Where does your gearbox leak? Overpressure due to poor venting can cause a leak but often it's something else- generally seals.

At this stage not 100% sure, but suspect the usual selector seals.

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Hi Malcolm,

the selector seals are a serious pain in the posterior.

Some people have had success fitting Q seals - these have a cross section like a four leaf lcover and yhus have two contact areas on ID and OD.

Annoyingly mine still leaked.

I fixed my leak by accessing the area above the rods and putting a plastic tie strap around each rod. This caused the oil to drip off before it could escape out the back.

Marco (Z320) did a proper engineering solution and fitted tiny lip seals. This required a fair bit on ingenuity.

Try a search for the topics

 

Roger 

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10 minutes ago, RogerH said:

Some people have had success fitting Q seals - these have a cross section like a four leaf lcover and yhus have two contact areas on ID and OD.

Annoyingly mine still leaked.

Hi Roger,

Yes I've read your previous thread on the Q seals. And would be probably go down that route as a matter of course.

I know you say it still leaked, but did they help?

I havent got the top off yet, still at the chalk powder tracing stage.

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Even though I have a gearbox  dip stick - My gearbox still 'breathes' through the selector shafts.

 

Peter W

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Hi Malcolm,

      essentially the Q seals did not work for me. It took some time to migrate down the rods before leaking again. This gave the feeling that they were working.

I still have them fitted. The tie wrpas in the top cavity are certainly working - but the cavity will be filling with oil.

At some stage I shall do the same mod as Marco.

It is amazing that the oil can move along apprx 4" of rod and then drip outside.

On a positive note the oil running along the rod keeps the rod/ali casting from wearing out.

 

Roger

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I have managed to stop the leak on the rods.

The o rings that are supplied are too small for the recess that they fit into, if the ring moves it will actually pump oil out. The ring needs to be either a better section to fill the recess properly, I have fitted the quad seals with nylon backup washes to stop the seals moving, this has seemed to have worked. Mentioned in a previous thread.

I also found that the front seal on the input shaft can leak, this has been because the bearing has a circlip that can turn in use, it has to be positioned so the slot co insides with the return hole in the casting, or the circlip will block the oils return to the box. Of course there is no mention of the importance of this in the manual.

John

IMG_2275_LI (2).jpg

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