Front Axle Not Engaging

[hellpounder]

[1986 M934A1]

I've been trying to engage the front axle, but it doesn't appear to be working. The switch on the dash will flip once I've built up to 90psi, light will come on, but nothing else happens. Switching to low range doesn't do anything either. After investigating, I see where two yellow lines that went to the valve with the actuator have been cut and capped, and there is a third black line that goes from the valve to the back of the transfercase.



Someone told me I could bypass this by capping the line that has constant air pressure and connecting the other two lines from the valve together, then I should be able to just flip the switch on the dash at will, regardless of high or low range. After testing, the middle yellow line held constant pressure, the right yellow line and the left black line did not, so I connected them, built up pressure to 90psi, and still no engagement. I can hear blowoff occuring at the switch when I flip it off, but nothing happens besides the light coming on.

I tested, and the front driveshaft does spin when going in forward and reverse, regardless of if the switch is on or not.

I'm still new to these, I've only had it a couple weeks, and haven't found much more pertinent information besides the clutch possibly being broken. It's supposed again the end of next week, and this is my only winter vehicle at the moment, so I'm trying to be as prepared for that as I can.

Also, what are signs that it is working correctly? Sounds, feelings when I flip the switch, etc.

 

[hellpounder]

After a lot of looking around, I got a hold of Jim Cox at Army 6x6, who walked me through testing. I followed the black line pictured above to the back of the transfer case, and noticed the piston housing, and disassembled it by bending the locking tabs on the bolt heads back with a hammer and flathead, then used a small 1/4 ratchet and an 11mm socket on the 4 bolts. A small amount of oil leaked out, but it was very minor. https://www.steelsoldiers.com/threa...transfer-case-rebuilding-error-solved.149997/ I followed along with this post to ensure it was not installed backwards, and that tyhe copper washers and o-ring for the piston were in good condition. There was only a single copper washer, which looked spent, and the o-ring was fraying on the edges. I spoke with Army 6x6 again and was sent a rebuild kit that consisted of the 2 copper washers [which just stack on top of each other, but I recommend inserting them one at a time] and the o-ring [make sure to lube it with some of the oil that's there, and install it the correct direction so that the air catches the back of it].

After this, I made sure the black line that goes to the back of the transfer case/front axle engagement piston was connected to the yellow line that goes up to the dash switch, and left the middle line that comes off the framerail capped, so that the front axle only engages/disengages when I flip the dash switch, and the linear valve is bypassed.

I borrowed a 15 ton bottle jack, jacked up the front passenger tire and started the truck. The front axle engagement switch on the dash was flipped off, and I was able to freehand spin the tire. Once the truck got to 90 psi, I flipped the switch, it held pressure, and I tried spinning the tire, which was now locked. I repeated this twice, and it behaved consistently.

I did deal with the PPV on the wet tank freezing once it hit below 0, and preventing me from engaging the front axle, which I explain more about here: https://www.steelsoldiers.com/threads/air-lines-frozen.225489/
But, this was as simple as taking a heat gun to it for about 30 seconds, then I heard the clunk of the piston engaging. Drove around for a bit, on and offroad, for a couple days on and off, and it did excellent. I keep a cordless heatgun in the truck for thawing.

I know many people here probably already know about all of this, but hopefully this helps out another noob in the future.