Weird air system issue

[KF6-BusFan]

So I have to assume the issue is inside the drum somewhere?  Any advice on what could be keeping the rod from disengaging? 

Did you get to the bottom of this?  The DD3 air chamber needs air supplied to what they call the "locking port" in order to unlock the brakes. This comes from the inversion valve, which is commanded by your push/pull parking valve.

The locking mechanism inside the air chamber is a sort of ratchet, so sometimes after applying "lock" air to unlock the lock, you have to pulse the main brake application air, to push the rod out briefly and then allow it to retract.

While working on mine, on the bench, I would test by applying air from a compressor/tank to the lock port, and every time the rod would just retract using the internal spring. But when installed, sometimes I have to pulse the brake pedal.

Hope that helps.

[JT4SC]

Did you get to the bottom of this?  The DD3 air chamber needs air supplied to what they call the "locking port" in order to unlock the brakes. This comes from the inversion valve, which is commanded by your push/pull parking valve.

The locking mechanism inside the air chamber is a sort of ratchet, so sometimes after applying "lock" air to unlock the lock, you have to pulse the main brake application air, to push the rod out briefly and then allow it to retract.

While working on mine, on the bench, I would test by applying air from a compressor/tank to the lock port, and every time the rod would just retract using the internal spring. But when installed, sometimes I have to pulse the brake pedal.

Hope that helps.

Hey guys,

Well I've kind of fixed it, the bus is now building air and not stopping at ~100psi, everything is doing what it's supposed to do.  The only issue is I don't know exactly what fixed it. What I do know is I had a bunch of deferred maintenance that all lead to this, and I'm slowly (and expensively) fixing it. 

What I THINK was most likely the cause of the issue was actually the air dryer.  I'm embarrassed to say this but in almost 20 years of owning this coach I have never changed the air dryer cartridge.  Why, you ask, would I be dumb enough not to do this?  Honestly because I didn't know I was supposed to.  I don't come from a bus mechanic/driver/enthusiast background, I bought this bus as a 27 year old kid who had spent exactly 1 night RV'ing prior to buying the coach.  So, to say I've learned a lot about busses over the years would be an understatement, but I just had not yet learned about the air system and maintenance.  When I had the oil changed I would ask them to check the brakes and air system, and they would always say they're good, but I didn't take the time to learn it myself until now. 

So, all that to say I've done a lot of work:

- I've (so far) gone thru 3 axles, brake and air systems (passenger drive axle, driver and passenger front axles), changed seals, brake pads, drum and brake chamber on the passenger drive axle, front hub caps, air bags and shocks, air relay and air pressure regulator on the drive axle, check valve that I think had failed on the rear air tank, deleted the air system on the AC belt tensioner in the engine bay (it had been leaking air - going to eventually get rid of the entire OTR air system and go to a mini split), replaced the governor and unloader valve on the air compressor, and changed the air dryer.

Still need to through the driver side drive axle and both tag axles.  VERY costly and very time consuming, but it needs to be done. 

Thank you all again for all your help, I would have been defeated in the bus game a long time ago if it wasn't for you.