Air Leak bypass

[Holt Slaughter]

I recently bought a BMY M923A2, drove it about 30 miles home and had no issues. Parked the unit for a few days and when I cranked it again it would not build air past 60psi. At 60-62psi I can hear air coming from the intake stack. I have verified that the air is coming from the center vent line on the stack, the smaller plastic flex line. If I am correct, this should be the air system for accessories and part of he units vent system. The larger two braded lines should be the front/rear axle and brake vents. Is there a way to bypass the accessory tank and air circuits so I am able to move the unit. Where the unit is currently parked limits my test and trace the air leak. Any help would be great.

 

[silverstate55]

Sounds like the PPV (Pressure Protection Valve), lots of threads on here about it. I’d start by replacing that and then servicing (or swapping) the Air Dryer.

 

[Mullaney]

I recently bought a BMY M923A2, drove it about 30 miles home and had no issues. Parked the unit for a few days and when I cranked it again it would not build air past 60psi. At 60-62psi I can hear air coming from the intake stack. I have verified that the air is coming from the center vent line on the stack, the smaller plastic flex line. If I am correct, this should be the air system for accessories and part of he units vent system. The larger two braded lines should be the front/rear axle and brake vents. Is there a way to bypass the accessory tank and air circuits so I am able to move the unit. Where the unit is currently parked limits my test and trace the air leak. Any help would be great.

.
I definitely agree with silverstate55 . That should be a fairly easy fix too.

If you happen to have an air compressor at your place, you might connect it to the truck one day. Air goes in at the drivers side front glad hand to charge (pressurize) the air system. CHOCK THE WHEELS and limit pressure to 150 psi. With "house air" connected to the truck, you can crawl around under the hood, under the dash, and under the truck listening for any leaks that you might find. A spray bottle of dish soap on every line isn't a bad thing. She will blow bubbles if you locate a leak. The noise (motor) off but the air system charged is a nice way to PD air systems...

 

[Holt Slaughter]

Sounds like the PPV (Pressure Protection Valve), lots of threads on here about it. I’d start by replacing that and then servicing (or swapping) the Air Dryer.

ill look into that. Do you now if i can bypass that whole air circuit so i can build enough pressure to release the brakes? i dont want to bypass something that will cause a engine or driveline failure. is the fuel system on these trucks pressurized tank forward? if it is, does the accessory air circuit supply it? im familiar with RG 31/33 and Husky systems and basing my thoughts on them. Thanks

 

[Holt Slaughter]

.
I definitely agree with silverstate55 . That should be a fairly easy fix too.

If you happen to have an air compressor at your place, you might connect it to the truck one day. Air goes in at the drivers side front glad hand to charge (pressurize) the air system. CHOCK THE WHEELS and limit pressure to 150 psi. With "house air" connected to the truck, you can crawl around under the hood, under the dash, and under the truck listening for any leaks that you might find. A spray bottle of dish soap on every line isn't a bad thing. She will blow bubbles if you locate a leak. The noise (motor) off but the air system charged is a nice way to PD air systems...

Unfourtantly the unit is not near my shop or accessible with a service truck. I did a full air system inspection when the problem fist arose and the only air I could find leaking was through the smaller vent line. if i remove the accessory air circuit from the system, will i be able to move the unit without damaging other systems? thanks

 

[Mullaney]

Unfourtantly the unit is not near my shop or accessible with a service truck. I did a full air system inspection when the problem fist arose and the only air I could find leaking was through the smaller vent line. if i remove the accessory air circuit from the system, will i be able to move the unit without damaging other systems? thanks

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If you are building air - but not enough to move the truck - you could cage the brakes and move it around in your yard. DEFINITELY don't want to get out on the road that way, but in a pinch it would work.

 

[juanprado]

Where are you in La? I am in New Orleans and work in Baton Rouge and have a m923

 

[simp5782]

Does the truck vent air to the intake with the parking brake off and with it on?

It vents air there for separate reasons given the position of the brake.

Under your truck close your shut off valve on the wet tank on the passengers side Under the transfer case. Close each one and see which one let's you hold air versus dumping it. There are just 2.

Rear axles have 6 to 8 cotton jacket lines. Yes there are 2 that are vents but the cross feed air supply lines are also cotton jacket.

Drivers side of the truck. Behind the air box on the inside of the frame there is a block with air fittings going to it. It will have a large 5/8" line going to it. Start by removing each line and see which one has the air coming down the vent this will help narrow it down.

 

[Holt Slaughter]

Thanks to everybody for the suggestions. I just capped off the PPV until i have the time to go through the accessories and find the leak.

 

[98G]

Thanks to everybody for the suggestions. I just capped off the PPV until i have the time to go through the accessories and find the leak.

Note that your air dryer, air governor, horn, wipers, and air shift Tcase are all behind the PPV.

I realize I may be pointing out the obvious. It may not be obvious to everyone.