armytruckdiesel

I'll try this again as my original post did not show up from this morning.
On my M812 bridge truck equipped with the 5spd manual trans there is an assy. on the passenger side of the upper part of the trans which makes a hissing noise when the trans is shifted into reverse. The vent tube is constantly blowing air unless the trans is shifted into reverse. I have been told on another post that this is the sprag failing and it needs replaced?
1) How does this air shift work? Any pictures?
2) How hard is this unit to replace- Any tricks from anyones experiences?
3) Where do I look for this part and how much is one typically
I would rather purchase a new assy. if available and know it's fixed for good.
thanks,
Andy

Latrine_Commander

The seal is bad on the valve on the side of the transmission. Air is bypassing ans coming out of the tee that is between the valves.

You can disconnect the incoming line and and block the air.

John

acetomatoco

It is a switch (air) which shifts the sprag from forward to reverse...It can be removed and the leaking diaphragm replaced..If you disconnect it, the sprag will not work in either direction as it requires air to apply in either forward or reverse..You shouldn't hurt anything, you just won't have front axle drive, as I understand it... Shutting off the air is like putting the sprag in neutral...so you can run free wheeling hubs, if you are among the lucky few who have the 5 ton version...

armytruckdiesel

Thanks for the help. I'll clean the assy. and replace the gaskets with new units.
Andy