M817 front wheel assist not working

[Darrick23]

Front axle not pulling when stuck. Drive shaft not spinning either.. is there some sort of shutout in the transfercase or is it broke? Thanks!

 

[porkysplace]

It is probably the sprag needing adjusting or the air valve gummed up .
These threads may help.
[h=1]front axle not engaging[/h]
[h=1]How to test if front axle is working[/h]
[h=1]M817 Air Blowing out of Top of Transmission[/h]
[h=1]6x6 only engaging in reverse[/h]
[h=1]Front wheel drive[/h]
[h=1]Frustrating 809-series sprag![/h]

 

[Darrick23]

I read all the threads and info was very good. MY M817 only has 4x4 in reverse. I cleaned and tested poppet valves, unhooked sprag air lines and left on the air supply line and it released air in both directions as it should. hooked sprag lines back up and it only clunks when shipfing in reverse and shoots a little blast of air out when shifting out of reverse. does nothing at all in forwards. No air leaking from anywhere, sprag or poppets relief port. if a sprag seal is bad wouldnt you hear air leaking when in forward?

 

[Floridianson]

It shifts out of reverse sprag when you go in to neutral. People have said you have to shift in to first first but this is incorrect. Yes poppet valve can go bad with O rings or gaskets. I have posted that is if you have a 809 series remove the battery box cover. Then with a real long 1/4 extension and if I remember 7/16 swivel socket tighten all eight of the bolts that hold the poppet valve to the trans. and together. Most of my 809's needed the sprag air cylinder rebuilt. The air would either leak when in reverse or neutral but not both on mine. Yes you could have both preformed packing go bad. If there is not enough air pressure to hold the sprag piston fully engaged then we have a problem. The sprag piston has springs on both sides of the piston cups and it needs full air pressure to keep the sprag shaft fully engaged. Yes there are many threads and I have posted some to on rebuilding the sprag cylinder.
Hope you can find good threads on sprag cylinder rebuild. Will help and say this after removing top four bolts on cylinder cap then pull off the cylinder from the piston. When installing it back we need to install the piston in the cylinder first and then install both together on the shaft.
Also do not bend the four locking tabs back over on four bolts on the cylinder cap till you check that the copper rings are not leaking.