MACKTRUCKS4 Posted July 2, 2015 Share Posted July 2, 2015 My 1964 B-model has roto-chambers that work the parking brake on the rear axle only. These are not maxi brakes. When i build air pressure and release the parking brake (single valve on the dash) the brakes release just fine but when I push down on the brake pedal hard, it pops the valve out. If I hold down on the foot valve, I don't hear any air leaking anywhere and I try to push the parking brake in, there is no air at the valve and it won't release. I let up on the foot valve and it works. I changed the foot valve but no luck. It looks like the dash valve is new so I'm thinking someone else tried that but no help. I'm thinking a check valve or maybe another valve somewhere is hanging up. Any thoughts? Quote Live every day like it's your last, because one of these days, it will be. Link to comment https://www.bigmacktrucks.com/topic/40747-parking-brake-issue/ Share on other sites More sharing options...
MACKTRUCKS4 Posted July 17, 2015 Author Share Posted July 17, 2015 Ok, now that I stumped the best of you's, I think I found the problem but I for the life of me , can't figure out why. On the dash valve there was 4 lines running into the valve. Supply, delivery, a line running to a dash valve that activates the tractor protection valve and the exhaust. Someone had a line running from the exhaust to the upper half of the foot valve, so when you pushed down on the foot valve, it would pop the valve out. The problem I have is the lines is a copper line just like the rest of the lines and it looks like it belongs there. Does anyone have any idea where this line should go? The exhaust line I get, just run it outside the cab to exhaust outside. But why was it hooked up to the foot valve? Remember this truck has roto-chambers and not maxi's.Now I know why no one had this happen to them. Someone connected the lines wrong. Quote Live every day like it's your last, because one of these days, it will be. Link to comment https://www.bigmacktrucks.com/topic/40747-parking-brake-issue/#findComment-296870 Share on other sites More sharing options...
fxfymn Posted July 19, 2015 Share Posted July 19, 2015 If all else fails you can contact the Mack museum for a shop drawing of the valve that should include what lines connect to what valve. Quote Money, sex, and fire; everybody thinks everyone else is getting more than they are! Link to comment https://www.bigmacktrucks.com/topic/40747-parking-brake-issue/#findComment-297122 Share on other sites More sharing options...
leversole Posted July 21, 2015 Share Posted July 21, 2015 I think there is a airline drawing in the vault on this site...I have the same setup as you, my valve has only three lines... Quote Link to comment https://www.bigmacktrucks.com/topic/40747-parking-brake-issue/#findComment-297298 Share on other sites More sharing options...
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