M916: Low Air Pressure

[fuzzytoaster]

Working at getting the new to me m916 operational. Mechanically it is great, 2011 rebuild, but won't build air past 30 psi on the rear tank, front tank gauge is inop. I've been reading the tms and searching SS to prepare for the recovery but I'm at a loss so far. I attempted to air up the system with a compressor but ran out of time for the day to confirm any noticeable change in psi on the gauge. My immediate thought is a bad air governor.

Syptoms:
-30 psi max
-no noticable major leaks (air drier pushing out air at bottom)
-airline valves checked and confirmed closed
-brake pedal works releasing air

I attempted to lubricate the governor with some tool oil and worked the brakes. Psi builds quickly to 30 psi then stops.

 

[NDT]

For sure it's the Bendix AD-2 air dryer. See the M916 Tech Tips page 17 for my post on the problem. There is a $10 kit that fixes the sneeze valve and all is well. When the valve weeps, it keeps the air compressor from building full air. Aftermarket kit is BEPCO 287053

 

[fuzzytoaster]

For sure it's the Bendix AD-2 air dryer. See the M916 Tech Tips page 17 for my post on the problem. There is a $10 kit that fixes the sneeze valve and all is well. When the valve weeps, it keeps the air compressor from building full air.

Thank you for confirming this act of murphy, now I can stop reading the TM's for a moment.

 

[NDT]

Let me know if you can find a kit in BCS. My understanding is that Barrman and I will cross paths here in Hou on Sunday, and I can send a kit back with him. Houston Truck Parts has them here. They are open Sat.

 

[fuzzytoaster]

Let me know if you can find a kit in BCS. My understanding is that Barrman and I will cross paths here in Hou on Sunday, and I can send a kit back with him. Houston Truck Parts has them here. They are open Sat.

I'm making a few calls as we speak. I'll let you know tonight.

 

[doghead]

-no noticable major leaks (air drier pushing out air at bottom)

Here's your problem most likely.

 

[goodguyzy]

It doesn't take much of a leak not to build pressure. I've had a couple of leaks and thought the truck could keep up but it wouldn't.

 

[fuzzytoaster]

To conclude this thread the dryer was the main culprit. Rebuilding the purge valve helped but ultimately the assembly has to be capped off to build enough pressure.