Differential not locking!
 

When I was leaving a warehouse today, I was going to pull out on the street, but I wasn't moving! Couldn't go forward, or backwards. Checked it out, my rear drive axle was 3 inches off of the ground because of the slope of the exit. So I went to lock the differential, and no dice. The dash computer showed it was locked, but it was not. Any ideas why it might not be locking?

Did you lock the power divider, or the axle? Do one or two of your axles have lockers?

Let me clarify, the interlock, so that both my drives would drive.

You sure it wasn't locked, you know how they work?

You can definitely still have wheels spin with the power divider locked.

Yes I am 100% sure it wasn't locking.

The rear drive axle was completely off the ground, so it had no contact of any kind with the ground, it would just spin. The front drive axle, was firmly on the ground. If it was locked in place, the front drive axle would of caused me to move, looking in the mirror only the rear drive axle was spinning, ontop of that when you flip that switch, you can actually hear it lock in place, there was no sound, I had someone stand next to it while I flipped the switch to hear it, no sound. I know it is air powered, so I am thinking maybe the air line is broken going to it? I don't know.

What I do know, is that if you flip that switch, both drive axles are supposed to turn!

You're absolutely right, was there any air leaks?

So none of the four front drive tires were moving at all?

A trick you could've done is back off the front drive brakes, and release the spring brakes. This forces the torque to go to the front drive tires.

Yeah there was no movement of any kind on the front drive axle. You mean let off the clutch a little with the breaks engaged then release the brakes? I will have to try that next time.

At first I kept putting concrete blocks down under the working drives, which did give me about 6 inches of forward movement, but eventually I lost all my progress when I rolled back to where I was initially :). Luckily they where taring up a part of the lot, and there was a crew there with a forklift. I asked them to push my trailer with the forklift, and that worked, pushed the entire rig forward until the working drive axle was back on terra firma.

That would of been really silly to call for a tow just because of a small slope leaving a warehouse lot!

But as for my original post, I am wondering if it is as simple as a airline, and if it is how hard is it to trace and fix it. Also as far as airleaks go, the funny thing is I do notice an air leak. But not in the rear. It is coming from the passenger side up near the stear somewhere. I checked out the air bag but I can't pin point it. I am pretty sure it isn't the air bag because all the air bags stay inflated at proper level, no one airbag is deflating any faster then the others. Though the air does run out fairly quickly when the truck isn't running. If I have it shut off for a good ten minutes, the air will drain down to about 55 PSI. Though it never drains enough to cause the trailer brakes to pop! Usually when I park I just pop the tractor brakes, and leave the trailer brakes disengaged. Even sitting for 10 hours with the truck not idling, the trailer never pops. The air will get down to about 50 to 55 psi and stay there.

As a matter of fact I am going to do a brake test right now to see if the trailer brakes will pop... Yeah they popped at about 20 psi. Truck is doing some wierd things though, wierd noises and shimmies now that the air is completely gone, I am just guessing it is the air bags settling down.

No I meant disable the front brakes from working at all by backing them off. Then pull OUT the yellow button and leave it out.

This forces the torque to go to the front axle, since the rear is locked via the brakes. Traction control systems do this in a different manner.