1078 LMTV air brakes COMPLETELY inoperative

[Jerds19]

I have a 1997 1078 that has worked flawlessly for 6 or so months since we got it.
This morning while making a 10 mile trip about halfway through the trip pressing the brake pedal failed to do ANYTHING, luckily I did't NEED the brakes and was able to downshift to about 5-10 mph when I pressed the emergency brake on the dash, and it did absolutely nothing, the truck continued to idle at about 2-3 mph regardless of brake pedal position or the emergency brake switch. I was able to shift into neutral and it stopped.
I was able to idle the vehicle off the road and to a safe place. I chocked the wheels, changed my underwear and am now trying to figure out what on Earth could make the brake system fail ENTIRELY.

If this has been covered in another thread, please please please slap me and give me the link so I can apologize and get this truck fixed!
Knowns:
Air pressure in front and rear are 100+ psi. Never dropped down. I opened all 3 purges and drained system entirely, not a drop of moisture came out. (we do this every few days)
With air pressure at zero emergency brake release button will not disengage so it appears to be working correctly.
Starting vehicle with tanks open so it has NO air pressure, put it into gear and it moves like the brakes are not even applied.
Closing tanks and letting pressure build in both tanks to 100+, still will idle around regardless of brake or emergency button.
When I first got vehicle to safe location on side of road the brakes smelled hot, even though they were not doing anything. (outside temperature is about 30 degrees, truck warmed for 15-20 minutes before driving and drove and stopped fine for first 10 minutes, then problem arose out of nowhere).
Pressing and releasing the brake peddle does create the "woosh" sound like normal.
There does now appear to be an air leak in the left rear brake system, this is new. When I charged the system up and turned the truck off and got out of it, I heard the leak, can't identify exactly what component it is leaking from though. Assuming this is related to the problem, possibly coincidence or cause.

If there is a flow chart I would be happy to run down it, I just couldn't find one in the TMs for brake FAILURE, only "increased braking distance" which keeps pointing to rear brakes not engaging.

What could cause the brake system to ENTIRELY fail in every way but still retain full air pressure?

 

[DiverDarrell]

You have big problems!! The air brake system is designed so that when it fails the park brakes are automatically set. Try completely airing down the system and see if this function works. If this doesn’t then it’s a place to start. Then I would check the tractor protection valves, treadle assembly, every airline, every drum assembly, every check valve, air dryer and every part connected to the brake system. I’d have this truck towed home and not attemp field repair until problem is found.

 

[Jerds19]

Thanks, we did air down completely and checked, brakes were non-existant, we aired it back up, brakes were still non-existant.
How do we "check" the valves and assemblies you mentioned?
The only leak is the slow leak by the left rear wheel, it still builds and holds air fine, so even if this leak is a problem it shouldn't take the whole system down, I wouldn't think...

 

[DiverDarrell]

Well you for sure have a major issue on your hands. I’d get into the TM’s and 100% go through your brake system. The park brake cans have a spring in them to activate then there is no air, for some reason your springs are not doing their job. My bet is you have more than one issue that has snowballed into your current situation. You need to take your wheels and drums off to look at the brake assemblies, that may provide more info to this puzzle. Perhaps all your brake pads have broken, or something along that line.

 

[porkysplace]

Since the rear don't engage with the parking control are the rear brakes caged ?

 

[Jerds19]

Negative on caging. Vehicle worked fine for last 6 months, we park it on a hill frequently so we know the emergency brake works properly (and chock the wheels) even sometimes in traffic at lights if I'm going to be there for a while I'll pop the E-brake on and it holds the vehicle quite well, more than once I've forgotten to turn it off and pressed the fuel and it won't budge until I remember to turn it off.

 

[NDT]

Given the temps in Austin are below freezing today, I suspect all of the brake actuators are frozen.

 

[porkysplace]

When was the last time the air dryer was serviced ?

 

[Jerds19]

Given the temps in Austin are below freezing today, I suspect all of the brake actuators are frozen.

It is cold out here, about 20ish degrees, but these things should be good to -40, 20 above should be like t-shirt weather for them shouldn't it?
I do assume that the temperature probably played a role since it is really the only thing that has changed in the last 6 months.

 

[98G]

It is cold out here, about 20ish degrees, but these things should be good to -40, 20 above should be like t-shirt weather for them shouldn't it?
I do assume that the temperature probably played a role since it is really the only thing that has changed in the last 6 months.

Your Original Post Said 30 degrees, and i was completely at a loss for what would cause this .

20 degrees changes the equation completely. They're frozen...

 

[Jerds19]

Your Original Post Said 30 degrees, and i was completely at a loss for what would cause this .

20 degrees changes the equation completely. They're frozen...

I'm rounding a bit here, this morning when it failed it was about 29 degrees according to weather history, currently we're sitting around 24 degrees, cold front is coming in.
I'm still thinking that these things should operate in the cold shouldn't they?

 

[Jerds19]

When was the last time the air dryer was serviced ?

Working on the answer to this.

Thank you and everyone else that is trying to help with this!

 

[bikeman]

I'm rounding a bit here, this morning when it failed it was about 29 degrees according to weather history, currently we're sitting around 24 degrees, cold front is coming in.
I'm still thinking that these things should operate in the cold shouldn't they?

They should, at 100% proper maintenance, but if there's even a small issue, it could be compounded. Absolutely 100% the brakes should be engaged with no air pressure. Since you're saying the parking brake is NOT engaging, then something is preventing that. Either frozen, or stuck due to grime, corrosion, bad fluids/grease, etc... Whatever is preventing the parking brake from engaging is also preventing the entire system from working right.

 

[98G]

Here's my best guess - you've got pockets of moisture throughout the system. It's frozen. This may trap high pressure air in the spring brakes not allowing them to deploy, or it may just block the moving parts from moving.

On the service side, you also have pockets of moisture. This prevents the air pressure from reaching the cans and actuating the brakes.

Or the moving parts may just be frozen in place.

Either way, the solution is to get it warm and working before moving it. Once warm and working, relocated to somewhere you can work on it, purge the air system and rebuild/replace the air dryer.

 

[Jerds19]

New update from the truck:
After the truck sat for a couple of hours the brakes started miraculously working a little bit, meaning flooring the brakes made them stop the vehicle slowly.
After the truck sat for a few more hours now the brakes will hold the vehicle in place and appear to be working properly (limited function test, moving it forward/backward and stopping within a 20-30ft run).

Is it possible that somehow during my 10 minute drive this morning the brakes got stuck partially applied while I was driving 45mph, and it induced a severe case of overheated and faded brakes? Now that they're cooling off things are working normally?
If so is there something that could be identified as a likely cause of brakes stuck partially on? (I didn't feel any drag while driving, so I assume they couldn't have been on more then 5-10% or I would have noticed something wrong).
Just a theory here obviously, I clearly don't know as much about air brakes as many of you do but armed with this new information it makes sense to me.

 

[98G]

Air is slowly making its way past the ice occlusion and/or the occlusion has possibly partially cleared.

 

[porkysplace]

New update from the truck:
After the truck sat for a couple of hours the brakes started miraculously working a little bit, meaning flooring the brakes made them stop the vehicle slowly.
After the truck sat for a few more hours now the brakes will hold the vehicle in place and appear to be working properly (limited function test, moving it forward/backward and stopping within a 20-30ft run).

Is it possible that somehow during my 10 minute drive this morning the brakes got stuck partially applied while I was driving 45mph, and it induced a severe case of overheated and faded brakes? Now that they're cooling off things are working normally?
If so is there something that could be identified as a likely cause of brakes stuck partially on? (I didn't feel any drag while driving, so I assume they couldn't have been on more then 5-10% or I would have noticed something wrong).
Just a theory here obviously, I clearly don't know as much about air brakes as many of you do but armed with this new information it makes sense to me.

As 98G pointed out moisture in the system , that is why I ask a few posts ago about servicing the air dryer. It sounds like you haven't serviced it since you owned the truck and if the moisture is froze it won't come out of the tanks when you drain them . I wouldn't drive the truck until you find the issues and correct them. It's a accident waiting to happen.

 

[Jerds19]

As 98G pointed out moisture in the system , that is why I ask a few posts ago about servicing the air dryer. It sounds like you haven't serviced it since you owned the truck and if the moisture is froze it won't come out of the tanks when you drain them . I wouldn't drive the truck until you find the issues and correct them.

I am completely with you on not driving it until we figure out WHY it happened, so we can make sure it doesn't happen again.
I am not the one that actually services the trucks, I haven't been able to get ahold of the person that did the oil change and services on it so I can't confirm if it was or was not ever touched.

 

[aleigh]

+1 to the wet air meets cold temps idea. And boy that must have been an UCE (underwear change event)...

 

[frank8003]

I didn't get far passed changed underwear
Scary read
...............and this is a truck for our military.