M931A2 primary air problem

[Redneck92]

Hi guys I´m back with another problem.

Today I tinkered with my electric a bit since somebody cut and rewired my light switch connector.

Long story short, I told my girlfriend to step on the brake pedal so I could watch the back brake lights. She stepped on it pretty hard and when she released it,
all primary air dumped out and the air warning buzzer came on.

So what could have happened?

When I shut off the primary tank on the wet tank the secondary builds air fine.

Condition as follows ( primary side closed on wet tank, secondary tank full )

- Secondary pressure stayes the same wether I open the parkingbrake or not.
- Secondary pressure stayes the same when I put in the spring brake override.
- Secondary pressure stayes the same wether I use the parking brake or the spring brake override.

When I shut the truck off secondary holds air.
As soon as I open the shutoff valve on the wet tank to the primary side I can hear air in the stack and the horn like sound it makes when you step on the brake till the wet tank is empty.

Where should I start looking for the problem?

Thanks in advance guys

 

[simp5782]

Brake pressure blew a diaphragm right out

 

[Redneck92]

That is not what I wanted to hear....

How ca I identify which diaphragm went out exactly?

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[simp5782]

That is not what I wanted to hear....

How ca I identify which diaphragm went out exactly?

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With the parking brake on does it loose air immediately?

With the parking brake OFF does it loose air immediately?

 

[Redneck92]

It looses air immediately wether the parking Brake is on or off.

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[simp5782]

It looses air immediately wether the parking Brake is on or off.

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At the brake pedal valve on the engine bay side. The very bottom line is the vent for the brake pedal. Remove that line and see if you have air coming from the brake pedal or the line itself.

You will need a 7/8" wrench.

There is no air to the spring brake diaphragms with the parking brake on unless the override on the dash is on.

A stuck treadle valve could be still applying the brakes

 

[Redneck92]

There is no air coming out of that Port nor the line

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[Redneck92]

The App does not send my pictures that I hat taken.... Idk why....

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[simp5782]

On the inside frame rail. behind the air pipe there is a block on the frame where all the vents meet. It's obvious cause a large 5/8" dot line will go from it to the intake pipe

You should have 2 from the rear and one or two to the front you can remove them each from that block and see which one has air venting from it.

 

[Redneck92]

Took a screenshot from one of your Videos.
Red arrow: no air from the line nor the Port.

Yellow arrow: there is little air flowing from the line if I take that line off. If I hold the line shut it will build a little bit of pressure but not much. Neither secondary nor primary gauge will move wether I hold it shut or not when the truck is running.

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[Redneck92]

On the inside frame rail. behind the air pipe there is a block on the frame where all the vents meet. It's obvious cause a large 5/8" dot line will go from it to the intake pipe

You should have 2 from the rear and one or two to the front you can remove them each from that block and see which one has air venting from it.

I'll check that tomorrow and report back.
Thank you for your Quick help with this.

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[Redneck92]

So, the Problem didn't leave me alone....

I went back to the truck and tested some stuff. I gave Shop air to the service gladhand and didn't hear any air leaking.

Then I removed the Shop air. Started the truck up and Opened the shutoff valve to the primary tank. Primary would not buikd air as before.

Then I stomped a few Times Hard on the Brake Pedal and pushed it to the floor and held it there. Suddenly the primary tank started to build pressure.

Both tanks Aired up as usual.

Then I released the Pedal and the pressure stayed the same.

I tested the parking breake, releasing and closing as it should. Then I drove the truck a few meters forward and rearward and used the brake Pedal. Stopped like before the Problem.

I drained the air completly from the truck.

Started it up and it aired up like nothing happened.


Could it be that indeed the treadlevalve was stuck?

Tomorrow I will test again if everything works like it should.

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[Mullaney]

So, the Problem didn't leave me alone....

I went back to the truck and tested some stuff. I gave Shop air to the service gladhand and didn't hear any air leaking.

Then I removed the Shop air. Started the truck up and Opened the shutoff valve to the primary tank. Primary would not buikd air as before.

Then I stomped a few Times Hard on the Brake Pedal and pushed it to the floor and held it there. Suddenly the primary tank started to build pressure.

Both tanks Aired up as usual.

Then I released the Pedal and the pressure stayed the same.

I tested the parking breake, releasing and closing as it should. Then I drove the truck a few meters forward and rearward and used the brake Pedal. Stopped like before the Problem.

I drained the air completly from the truck.

Started it up and it aired up like nothing happened.


Could it be that indeed the treadlevalve was stuck?

Tomorrow I will test again if everything works like it should.

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.
It might be some "crud" that made it out of the tank and into the supply lines. It could be gummy from something nasty in the air tanks or from the air dryer. Might be that the more you use it, the better it gets... It might also be good to add a few drops of Marvel Mystery Oil in the line out of the last tank in the line (under the drivers door to limber up or help soften up whatever gunk may be in your supply lines.

 

[Redneck92]

Didn't think of that. The original Checkvalves were all badly rustet. That stuff needs to go somewhere...

What is the easiest way to air up the truck With shop air?

In the P2P I saw that the rear emergency gladhand goes to the Trailer push valve unter the steering wheel and would then end in the wet tank.

Can I air it up that way? I think of disconnecting some exit lines from the tanks and some supply lines, one after another and blow out crud with the shop compressor?!

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[Mullaney]

Didn't think of that. The original Checkvalves were all badly rustet. That stuff needs to go somewhere...

What is the easiest way to air up the truck With shop air?

In the P2P I saw that the rear emergency gladhand goes to the Trailer push valve unter the steering wheel and would then end in the wet tank.

Can I air it up that way? I think of disconnecting some exit lines from the tanks and some supply lines, one after another and blow out crud with the shop compressor?!

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.
If you want to air up the truck - in search of leaks for example - the drivers front glad hand will "charge" the air system with house air. Regulate your pressure down to below 120# just in case you have your shop compressor set higher than that...

 

[Redneck92]

Okay thank you for the information. I will do that.

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