F86 gearbox air problem

My 1969 F86 has a problem with air leaking from rear of the gearbox. This has slowly got worse and the compressor needs about 5 minutes to pump up at start (loses all the air within a few minutes on stopping).

There is a small unit with rear plate at the top left rear of gearbox which has a hole leaking the air. Continuous flow at all times although when park brake is applied it seems to slow. I thought it may have been a safety blowout diaphram but when I block it you can not change gears.

Any ideas?

Lang

Lang, What gearbox do you have???

The original Volvo one??

Or a Roadranger???

I reckon Mammoth would have the answer Lang. A very long time ago I used to have to work on Volvos, my memory, which as you know, is shakey ar best, is that the range change cable goes down to a shutlle valve on the range change cylinder, on the end of the cable is a little who jar with O rings on it, could be that, if not Mammoth will be at Beenliegh but coming and going it would seem.

The box is the original Volvo 8 speed.

Just leaving now for Beenleigh so hope some wiser people than me can throw a bit of light on the subject.

Lang

You can get the air leak to stop by changing the range sometimes . ie leaks in low range change to hi , sooner than later though it will not let you change at all, easy job to change the o rings anyhow, provided it is not the vent line from the clutch servo going to the box (I'm sure this will have long gone.)

Thanks for the info.

Mammoth had a good look at it at the truck show and looks like the O rings on the range change. As you say an easy job and kits are available.

Lang

Lang, I will scan pages from the manual tonight and flick them to you, also exploded diagram of a bigger gearbox from parts book. Might also pay to clean the check valve in the top of the box while you're at it.
Also, if you have never changed the gearbox oil filter might be time for that as well. The filter hides behind a plate fixed by two bolts on the left side.