M1088A1 - All Service Brakes will not release

[jpfever]

Break down:
120 PSI in both front and rear tanks
Air temp - 27 degree F
Engine at operating temp
Park brake released - regular driving.

No leaks in the Air System

The event:
Normal driving conditions - 30 mph, coming up to a Stop sign, apply the brakes to slow vehicle, release the brake pedal to allow vehicle to roll a little further before actually applying the brakes to come to a complete stop.

At the point that I released the brake pedal, I could tell right away that the brakes had not released, the sound you normally hear when you release the brake pedal sounded soft, almost whisper like compared to the norm. I've looked at the TM, to no help at all, any thoughts?

 

[NDT]

Check the simplest thing first, is the vent on the front gladhand covers missing or plugged?

 

[jpfever]

Check the simplest thing first, is the vent on the front gladhand covers missing or plugged?

Forgot to mention:

I did check the front gladhand covers - all clear.

Service brakes did release at somepoint later in the morning, temp was still under 32 degrees.

 

[Suprman]

If its cold out and you have some moisture in the system it can freeze up and cause the same non releasing brakes. Sometimes letting the truck run and really warm up will defrost it.

 

[coachgeo]

time for air system antifreeze

 

[bikeman]

This is why you are supposed to drain the air tanks daily, and then close the valves. If moisture gets into the air lines it can freeze and create issues. The more likely (and dangerous) problem is when it freezes and holds the drums so they don't apply the brakes... suddenly you can't stop. Obviously can cause catastrophic issues.

 

[Suprman]

The air alcohol wont help. You need to upgrade the air dryer and get all the moisture out.

 

[jpfever]

that is what I was thinking.

 

[jpfever]

This is why you are supposed to drain the air tanks daily, and then close the valves. If moisture gets into the air lines it can freeze and create issues. The more likely (and dangerous) problem is when it freezes and holds the drums so they don't apply the brakes... suddenly you can't stop. Obviously can cause catastrophic issues.

The air tanks are drained daily, and the valves closed after the tanks are drained.

 

[Scrounger]

The symptom described sounds like moisture in the air system. To get some of the moisture out as Suprman has posted warming up the system is a place to start. With the truck running open the petcocks on the air tanks to drain them down, then close the valves. Allow them to refill and repeat the process several times. Remove the dummy glad hands from the rear glad hands. Open the emergency valve and purge the rear line. To clear the service side, open the valve, then get in the cab and apply the treadle valve several times. This will clear most of the moisture from the system.

If you don’t know when the dryer was serviced, it is time to do it.

 

[wheelspinner]

The brake shoes have frozen to the brake drums. A couple we’ll placed sledge hammer blows on the shoes will release them. When the truck is in operation they are warm. Any snow or dampness present when parked will then freeze

PS: make sure the wheels are chocked and release the parking brake before whacking them

 

[jpfever]

The brake shoes have frozen to the brake drums. A couple we’ll placed sledge hammer blows on the shoes will release them. When the truck is in operation they are warm. Any snow or dampness present when parked will then freeze

PS: make sure the wheels are chocked and release the parking brake before whacking them

I understand how the shoes can freeze to the drums when dampness is present and the vehicle is sitting. This is not the case: the vehicle was being driven at the time of failure. I agree with Suprman and Scrounger. If I get some time this weekend, I will take Scrounger's suggestion. At the same time, I have an upgraded air dryer that I need to install.

 

[Cgray]

I had same issue. I wasn’t draining tanks daily. I broke all the air lines where accessible and added air line conditioner/anti freeze. I haven’t had an issue since and have driven 300+ miles.

 

[wheelspinner]

I understand how the shoes can freeze to the drums when dampness is present and the vehicle is sitting. This is not the case: the vehicle was being driven at the time of failure. I agree with Suprman and Scrounger. If I get some time this weekend, I will take Scrounger's suggestion. At the same time, I have an upgraded air dryer that I need to install.

I agree now that I have reread your original situation.

 

[simp5782]

Air brake antifreeze will eat everything rubber in the system and dry it out and cause to more failures. You only use it in a real emergency. Even though it has some rubber conditioners in it with the older rubber that most of these trucks have it will put a hole in a diaphragm. I keep a bottle in an emergency like last weekend while loading a skidder in northern NY. I had an inlet elbow on the wet tank that had a small piece of ice in it and caused a no building issue. It froze cause of a slow purge system. Meaning that my air dryer may purge every 40 to 45 minutes when at idle due to no air loss from the tanks. Giving any water in the system a chance to freeze before the next compressor build cycle when it is below 0. For the air brake antifreeze Do not use much of it if you choose to do so.

 

[Awesomeness]

The symptom described sounds like moisture in the air system. To get some of the moisture out as Suprman has posted warming up the system is a place to start. With the truck running open the petcocks on the air tanks to drain them down, then close the valves. Allow them to refill and repeat the process several times. Remove the dummy glad hands from the rear glad hands. Open the emergency valve and purge the rear line. To clear the service side, open the valve, then get in the cab and apply the treadle valve several times. This will clear most of the moisture from the system.

1. When you guys drain the tanks, do you see water come out? I never have, with either the original air dryer or the new one I have installed now - I'm just making sure I'm not supposed to be. When I think of "drain tanks daily" on my shop air compressor, it's because I want to drain the water out of the tank so it doesn't rust out, so it's "drain tanks [of water] daily".

2. Is part of the reason for draining the tanks daily (and immediately after running the truck) to release to release the moist "cloud" of air that the system currently contains, so that it can't condense while sitting/cooling? In this context (and as opposed to question 1), this becomes "drain tanks [of humid air] daily", if so.

3. In your purging process above, when you say "Remove the... rear gladhands. Open the emergency valve and purge the rear line." What emergency valve are you referring to, since you just already instructed to remove the dummy glad hand off the emergency-side valve? I'm just making sure I'm following because your instructions use the word "valve" in several different ways (e.g. glad hand, brake pedal, dash knobs, tank petcocks, etc.).

 

[Cgray]

Air brake antifreeze will eat everything rubber in the system and dry it out and cause to more failures. You only use it in a real emergency. Even though it has some rubber conditioners in it with the older rubber that most of these trucks have it will put a hole in a diaphragm. I keep a bottle in an emergency like last weekend while loading a skidder in northern NY. I had an inlet elbow on the wet tank that had a small piece of ice in it and caused a no building issue. It froze cause of a slow purge system. Meaning that my air dryer may purge every 40 to 45 minutes when at idle due to no air loss from the tanks. Giving any water in the system a chance to freeze before the next compressor build cycle when it is below 0. For the air brake antifreeze Do not use much of it if you choose to do so.

I had had never used before. I have a 2005. Not being form the Midwest I had never experienced an issue such as this. Did a few weeks research and found that alcohol in system was not our friend here. As for the conditioner, I used for emergent reason but also thought for my year it was possibly not a bad choice.

Unfortunately being that I had never done it, I probably used too much of it.

Now that hat I am draining tanks after almost every use, I occasionally see a moisture cloud exit when driving on wet roads.

The one one positive thing I can say is that I have been down in the -20s without issue after the conditioner.

 

[Scrounger]

1. When you guys drain the tanks, do you see water come out? I never have, with either the original air dryer or the new one I have installed now - I'm just making sure I'm not supposed to be. When I think of "drain tanks daily" on my shop air compressor, it's because I want to drain the water out of the tank so it doesn't rust out, so it's "drain tanks [of water] daily".

2. Is part of the reason for draining the tanks daily (and immediately after running the truck) to release to release the moist "cloud" of air that the system currently contains, so that it can't condense while sitting/cooling? In this context (and as opposed to question 1), this becomes "drain tanks [of humid air] daily", if so.

3. In your purging process above, when you say "Remove the... rear gladhands. Open the emergency valve and purge the rear line." What emergency valve are you referring to, since you just already instructed to remove the dummy glad hand off the emergency-side valve? I'm just making sure I'm following because your instructions use the word "valve" in several different ways (e.g. glad hand, brake pedal, dash knobs, tank petcocks, etc.).

1. On a vehicle with a well-functioning air dryer you shouldn’t see any water when draining the air tanks. And just to clarify there are several air tanks in the system. The air comes from the compressor cooling somewhat as it reaches the dryer. The dryer then filters any oil out and condenses the air. One of the reasons that air dryers need servicing is as the filter collects oil and dirt they no longer filter as well. The air then goes to the wet tank. From the wet tank it then goes to the primary and secondary tanks. If everything is working most of the water is caught in the dryer and wet tank. There are several reasons for “drain tanks daily”. Some vehicles don’t have dryers, habit and for vehicles with a dryer, if lots of water comes out of the wet tank you know it is time for dryer servicing.

2. See above.

3. There are air lines running to the rear of the vehicle to operate trailer brakes. The glad hands have dummy covers that keep the dirt out that need to be removed to allow the air to flow freely. The emergency and service lines both have shut off valves at the rear by the glad hands. The emergency line has the same air pressure as the air system. The idea is to open the shut off valve at the rear to purge any moisture from the line. The service line only get air when the treadle valve is depressed, that is the brake peddle for those that didn’t know what it is called. By opening the service valve and depressing the treadle valve that will purge any air from that line. Just remember to close both valves and reinstall the dummy covers to keep the bugs out.

 

[Awesomeness]

3. ... The emergency and service lines both have shut off valves at the rear by the glad hands.

My M1078 does not have any human-operated valves near the rear gladhands (or front ones). Are you talking about some kind of system-operated valve under the truck? Or is that just a feature on M1088, or other tractor-style, vehicles?

 

[Scrounger]

My M1078 does not have any human-operated valves near the rear gladhands (or front ones). Are you talking about some kind of system-operated valve under the truck? Or is that just a feature on M1088, or other tractor-style, vehicles?

My mistake on the FMTV. The air supply valve for the trailer is on the dash. So, it makes them easier to purge. Just push the air valve on the dash, as in supplying a trailer with air, then apply the treadle valve. Pull dash air valve out and your done.

Disclaimer. I have a “little” bit of experience with air brake systems in general, just not a lot of experience with the FMTVs. All of the M44, M39, 800 series and M939 series of vehicles have valves on the rear by the glad hands.