spamfree4

No air drier in the system. All tanks have been drained, no excess water in any of them. The wet tank section tends to accumulate oil, but the air builds from a cold start to full pressure within the specification that the Mack service manual from that era indicates as OK. Check valves in each tank seem to work as they should. My first thought was that someone plumbed the air exit to the wrong tank segment and the system was being fed from only one tank. Testing has shown that is not the case, as all 4 tank segments fall to the same pressure when brake applications are made. The system has 2 tanks, with 2 drains per tank. The truck has been seriously neglected by previous owner(s) and the air piping is quite a circus. Reading all the comments, I suspect it might just be normal or have oversized pots, since it stops with minimal brake application when loaded to the top with dirt. Makes for a real fun time when trying to make K turns on a grade... It's off road only at this point. Thanks for all the input.

First thing I did. Front brakes had excessive slack, but after adjustment to minimum, no change. The rears are so tight you can barely see any motion when the brakes are applied. Parking spring brakes work as they should.

I have a 1970 DM685 dump truck which seems to run through it's air much faster than a modern truck. With the engine off and air pressure sitting at 130 PSI I can make 4 full pressure brake applications before the pressure drops to 65 PSI and the air warning turns on. There are 2 tanks in the system and all 4 segments drop to the same pressure, so I know it's using the full reservoir capacity. No leaks in the system, truck stops as it should when the brakes are used, no air leaking when the brakes are fully applied. Pressure builds from 0 to 130 in under 3 minutes when cold started. Total of 6 air chambers, not including the 2 parking / spring brakes. Is this just normal for a truck of this era?