Air leak

[NM 1078]

I've been daily driving my M1078 for a few months now with 0 problems. The other day when leaving my shop I heard a slight air leak but only once I had released parking brakes. Got it home still with a slight leak and shut it off. Started it up the next day and it was really blowing some air out of the front. Thought my gladhand bushings had gone bad so I purchased some new ones but to no avail. Then I thought maybe it was the gladhand handles with the vented dummy coupling. Anyways, I guess it's the check valve but my brakes release when I need them to, nothing is seized up and I'm only having air escape past the gladhands when I release the brakes. If it was the check valve wouldn't it be releasing air all the time if the truck is running or only when the brakes are released?

 

[Ronmar]

I've been daily driving my M1078 for a few months now with 0 problems. The other day when leaving my shop I heard a slight air leak but only once I had released parking brakes. Got it home still with a slight leak and shut it off. Started it up the next day and it was really blowing some air out of the front. Thought my gladhand bushings had gone bad so I purchased some new ones but to no avail. Then I thought maybe it was the gladhand handles with the vented dummy coupling. Anyways, I guess it's the check valve but my brakes release when I need them to, nothing is seized up and I'm only having air escape past the gladhands when I release the brakes. If it was the check valve wouldn't it be releasing air all the time if the truck is running or only when the brakes are released?

A 2way checkvalve has 2 inputs and a single output. Whichever input is greater slides the core out of the way and feeds the output.

your issue is the top 2way checkvalve under the drivers floor(behind the grill). When you release the brakes, you APPLY park air to one side of that 2way. The other input of the 2way connects down to that red front gladhand. The center output of the 2way feeds your park brakes. So either your park air control or a towing vehicles trailer air control can release the brakes. The air feed to presurize the air system on your truck from a towing vehicle is Td off that line near the red gladhand thru a checkvalve So a towing vehicle can charge your air system.

what is happening is you are applying park air and it is leaking past the core of the 2way and escaping thru the vented front gladhand. If your gladhand wasn’t vented, that leaking air would pressurize that line like a small air tank, and when you released your park air control in the dash, to set the parking brake, this stored air would flip the core and keep the parking brakes released just as a towing vehicle would with their park and trailer controls on.

this will keep your park brakes from setting until all that stored air leaks away. The giveaway for this is you release the park air to set the brakes, and the park and emer lights don’t come on

i would pull out that 2way and first disassemble it and look for some crap in it. But ods are it is just old and you will need to replace it…


A clogged blue service gladhand works the same way in that the line stores air like a tank if the 2way leaks past. Except in this case, you step on the brakes, the service air applies the brakes and charges that line to the gladhand, and when you release the pedal, that stored air continues to apply the brakes via the 2way, just like a towing vehicle would… untill the air leaks away.

common issue, thats why the gladhands must be vented…

i did a video on deleting those gladhands that explains how they interact and shows you the parts locations… the top 2way is almost easier to access by removing the grill…

 

[coachgeo]

Going by your avatar image... guessing you have an A0 truck with 3116. So it has cab ride air bags. My guess if it is not actually up front at glad hands etc.. is the air lines too the cab air bags..... fittings in that area.... or the air bag itself. Also could be the valve that determines what is "level" for cab air bags.

 

[NM 1078]

A 2way checkvalve has 2 inputs and a single output. Whichever input is greater slides the core out of the way and feeds the output.

your issue is the top 2way checkvalve under the drivers floor(behind the grill). When you release the brakes, you APPLY park air to one side of that 2way. The other input of the 2way connects down to that red front gladhand. The center output of the 2way feeds your park brakes. So either your park air control or a towing vehicles trailer air control can release the brakes. The air feed to presurize the air system on your truck from a towing vehicle is Td off that line near the red gladhand thru a checkvalve So a towing vehicle can charge your air system.

what is happening is you are applying park air and it is leaking past the core of the 2way and escaping thru the vented front gladhand. If your gladhand wasn’t vented, that leaking air would pressurize that line like a small air tank, and when you released your park air control in the dash, to set the parking brake, this stored air would flip the core and keep the parking brakes released just as a towing vehicle would with their park and trailer controls on.

this will keep your park brakes from setting until all that stored air leaks away. The giveaway for this is you release the park air to set the brakes, and the park and emer lights don’t come on

i would pull out that 2way and first disassemble it and look for some crap in it. But ods are it is just old and you will need to replace it…


A clogged blue service gladhand works the same way in that the line stores air like a tank if the 2way leaks past. Except in this case, you step on the brakes, the service air applies the brakes and charges that line to the gladhand, and when you release the pedal, that stored air continues to apply the brakes via the 2way, just like a towing vehicle would… untill the air leaks away.

common issue, thats why the gladhands must be vented…

i did a video on deleting those gladhands that explains how they interact and shows you the parts locations… the top 2way is almost easier to access by removing the grill…

Thanks I'll give that a try and see if I can get it working. If not I'll call the S&S shop and see if they can give me a hand with it. Rather do it myself though.

 

[NM 1078]

Going by your avatar image... guessing you have an A0 truck with 3116. So it has cab ride air bags. My guess if it is not actually up front at glad hands etc.. is the air lines too the cab air bags..... fittings in that area.... or the air bag itself. Also could be the valve that determines what is "level" for cab air bags.

Thanks. It's actually an A1 with the 3126 in it.

 

[Ronmar]

Wait a minute, release which brakes? release park brake or release brake pedal? I think I may have misread your initial post…

i thought you had determined that the air was COMING FROM THE FRONT GLADHANDS…

The vent for the treadle valve(brake pedal actuates treadle valve) is directly above the front glad hands up behind the grill above the radiator. When you apply the pedal it sends pri/sec tank air down the pri/sec service lines To apply the brakes. When you release the pedal it vents the service lines thru that vent to release the brakes. Closer to the brakes are QR valves or relay valves that release the air quicker instead of the air having to flow all the way back thru the treadle valve.

if the supply side of the treadle valve(part opened by the pedal being pressed) is leaking and the pedal is not pressed, this air will leak out that vent in front of the radiator untill you press the pedal…

 

[NM 1078]

Wait a minute, release which brakes? release park brake or release brake pedal? I think I may have misread your initial post…

i thought you had determined that the air was COMING FROM THE FRONT GLADHANDS…

The vent for the treadle valve(brake pedal actuates treadle valve) is directly above the front glad hands up behind the grill above the radiator. When you apply the pedal it sends pri/sec tank air down the pri/sec service lines To apply the brakes. When you release the pedal it vents the service lines thru that vent to release the brakes. Closer to the brakes are QR valves or relay valves that release the air quicker instead of the air having to flow all the way back thru the treadle valve.

if the supply side of the treadle valve(part opened by the pedal being pressed) is leaking and the pedal is not pressed, this air will leak out that vent in front of the radiator untill you press the pedal…

If the truck is idling and I release the yellow supply knob so that the truck isn't in park, I have air escaping the emergency gladhand at the fitting off of the side of the gladhand handle. (The section removed for towing). I originally thought it was the bushing between the gladhand and the handle. Ended up being air escaping past the vent with the small crushed on cap. It doesn't leak when the truck is idling in park, only when the supply air knob is pressed in and your ready to drive.

 

[Ronmar]

If the truck is idling and I release the yellow supply knob so that the truck isn't in park, I have air escaping the emergency gladhand at the fitting off of the side of the gladhand handle. (The section removed for towing). I originally thought it was the bushing between the gladhand and the handle. Ended up being air escaping past the vent with the small crushed on cap. It doesn't leak when the truck is idling in park, only when the supply air knob is pressed in and your ready to drive.

Ok, so my first description was correct. When you push in the park control you send park air thru a 2way(behind drivers grill) and on to the anti-compounding valve that in turn sends air to compress the park springs/release the park brakes. Watch that video I linked to and you will get an idea where the valve is and how to access it. I would pull that 2way apart and clean it first, but they are not horribly expensive…