M816 Wrecker Brake issues

[CombatJack]

All, the wrecker I bought a while back has never had brakes since I bought it (i have only used it once, and used the hand brake to stop it, since i was not really going anywhere, just pulled out of barn and moved a limb). The guy i got it from said it had "bad brakes". I filled the Master Cylinder this past weekend and bled all of the brakes. They worked GREAT. I can stop it easily, and i see no leaks. BUT..... here is where it gets weird...... Once i start the truck and it warms up, I put it in gear to drive, and the brakes are LOCKED up. I can't move it an inch. No matter what gear. I can push the brake pedal to try to release them, and i can set the brake with the push button on the dash, then release it, etc and you can hear the air releasing, etc as i am doing all o this. Eventually, I will push the brake just right, or hit the push button just right, or just cuss loud enough, and it releases somehow, and I am able to drive around like nothing happened. This had NEVER happened before until I filled the master cylinder and bled the brakes, but it makes no sense how that would affect this issue..... anyone have any ideas as to what I did or what might be happening? I am new-ish to 5 tons and havent opened the manual to troubleshoot yet (this only happened this past weekend).

Thanks in advance if anyone has ideas.

-jack

 

[Floridianson]

Yea if I used the push button brake when I used the crane sometimes I had to hit the brake peddle hard a couple of times to get the push button to release. We push the button only to set not release the brakes if I remember. You did bleed master then air pack then wheels right?