Customer states that brakes fade out if you hold them down. Went and looked at it and found it had lost a brake pad and the pistons pushed out. No fluid left in system. Resealed the caliper, put new pads on, and bled system. Still having the same issue. The brakes are air over juice. I have zero air leaks and no fluid leaks anymore. If I step on the pedal it will hold the loader on a hill for about 5 seconds. Without lifting my foot off the pedal the brakes just slowly release like I lifted my foot. If you step back down immediately there are no brakes. If you wait 5 seconds or so they will work again. The system isn’t complicated. Air compressor makes 120 psi. Air is fed into a truck style treadle valve which feeds 2 single chamber brake cans which push the rods on 2 master cylinders sending fluid to the calipers. All I can think is that the master cylinders are leaking by internally but the odds of both of them failing together doesn’t make sense. Anyone run into this?
If the air can's aren't coming back and making the master cylinders let off, its got to be masters, unless there's air in the fluid system yet. Can someone see the cans, or can you tee a gauge into the air side to see that application pressure holds? One air can pancake leaking would make both leak off pressure, and you wouldn't hear it in the cab.
The cans and master cylinders are next to the transmission and not easy to see. I guess I need to put a gauge into the inlet of the cans and make sure I’m holding pressure there. That should tell me if the air side is completely functioning properly.
Have you checked your treadle valves for sticking? Oh wait you said this was a 621B the "B" series doesn't have air over hyd. So this must be a straight 621.
It says 621b on the lift arms and the tag calls it a 621zf. It is air over hydraulic. I took out the brake valve and checked it out. Nothing sticking. Talked to the dealer and he told that if the master cylinder was over extended it would damage the master and it would cause this issue. Originally the machine had spit out a brake pad and the pistons on that caliper pushed out too far and leaked all the fluid out.
How is air pressure
118-119. Builds air from zero fairly quickly and no air leaks that I can hear or see on the gauge
Does the air pressure hold while you apply the brakes? Have you tried suppling shop air to machine and seeing if that helps? I would say that one or both master cylinders are leaking by.
Haven’t tried shop air but the air pressure from the machine holds perfectly which I why I’m becoming convinced that it’s on the hydraulic side
I'm not real familiar with this machine but others that use air over hyd. these systems are master cylinder failure. Bad Bob