M931a1 6x6

[Nick1983]

I have a 1986 M931a1 truck and I replaced the modulator cable back in the summer. Did not get to really drive it much after that do to fixing some other things on the truck. Got it out the other day and noticed that when I put it in reverse it starts out okay and then starts jerking when I apply the brakes and will stall out almost instantly if you don't get it back into neutral. I was watching the rear wheels and they were trying to turn while the brake was applied. Does anyone have any idea what could be causing this. Modulator cable it's set per the manual but not saying I did not do something wrong.

 

[M813rc]

I'm not quite clear on what's happening with your truck. Do all the rear wheels turn initially and then lock up, or is one or more staying locked?

If one or more is staying locked at first, these tractors are notorious for sticking the rear brakes to the drums due to moisture if they sit for a while.
When mine do that, I can usually break them loose by putting the truck in gear and gently running the RPMs up in reverse, then doing the same in 1st. A couple of back-and-forths like that usually breaks them loose, each with a bang, and usually not all together. On one of my trucks the right far rear seems to be the stickiest and usually has to get dragged a couple of feet before it breaks loose.
If the back and forth doesn't work, you may have to give the drums a few good whacks with a big hammer.

Cheers

 

[Nick1983]

I'm not quite clear on what's happening with your truck. Do all the rear wheels turn initially and then lock up, or is one or more staying locked?

If one or more is staying locked at first, these tractors are notorious for sticking the rear brakes to the drums due to moisture if they sit for a while.
When mine do that, I can usually break them loose by putting the truck in gear and gently running the RPMs up in reverse, then doing the same in 1st. A couple of back-and-forths like that usually breaks them loose, each with a bang, and usually not all together. On one of my trucks the right far rear seems to be the stickiest and usually has to get dragged a couple of feet before it breaks loose.
If the back and forth doesn't work, you may have to give the drums a few good whacks with a big hammer.

Cheers

It's not the brakes sticking. I can put it in reverse and let off the brakes and it will start pulling itself with little to no throttle on flat ground. At that point if I re apply the brakes and stop the truck it keeps trying to pull itself and then if you don't let off the brakes it will stall out. When driving forward I have issues. This is all in high range as I was told not to operate the truck in reverse in low range do to the chances off destroying the transfer case.