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1952 Mack A-30H brake problem



1) I am new to the forum and I am also a new caretaker of a 1952 A-30H dump truck. I am having an issue with the hydraulic brakes. So I will try to make this short as possible. The truck was running/driving fine without any issues. Brakes were firm and responsive. I noticed that there was not any stop lights. I changed the pressure switch (cold/hot) and this fixed the light problem. I was careful (or I thought I was) to not allow any air into the system when I changed the switch. However no brakes. I thought maybe air in the system so I bled the system(top of hydro-booster and all wheels top and bottom) If I pump the brakes I can build resistance and it will hold and not leak off. If I ease off the pedal slightly and reapply it holds and does not leak off. However if I release the pedal completely and reapply it goes directly to the floor, no resistance, no stop. I checked for a vacuum leak and there does not appear to be any. I am not familiar with the hydro-boost system but I find it hard to believe changing the switch for the lights would result in such a major failure.

2) I would like to locate a service manual for the A-30 if such an animal exists.

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