M923a2 parking brake lockup.

[maxtor]

Typo error,,, should read parking brake lockup.

I thought I would start a new thread on my problem, because the other thread involving the same issues was remedied, mine is not. Our M923a2 had been working fine. Now the truck will not move because the brakes are locked on. By depressing the spring brake control release valve, I can move the truck normally forward and in reverse. When I pull out the valve, the brakes lock up and truck will not move.
I have searched the TM's on this issue and did not find anything to solve the problem. I did read about a "Glad Hand" but I have no idea what it looks like. I have done searches and found nothing. There is a some information on google, but it does not seem to apply to our Military vehicles. Maybe this is not related to my problem, but I found that the Secondary air system air vent valve "the second from the top" was not releasing air in any volume. Also the third from the top, "air brake system wet tank valve" was not releasing much volume either, compared to the top and bottom valves. I had to use large amounts of WD40 to free the second and third valve, so they would turn out as far as the other two. Very little pressure in those two valves, especially the second one.
Any ideas on what is going on?
I am a commercial Airplane Pilot, and a retired IT supervisor, but totally clueless on trucks. I am trying to learn, but this is a whole new world.

BTW ,,, the roller by the hand brake moves fine up and down, so that is not our problem like it was on the earlier thread.

 

[porkysplace]

Have you downloaded and saved this to your computer ? M939_P2P.zip
It is searchable search for glad hands.

 

[maxtor]

No I did not have this zip file. Thanks.

 

[5tonman1971]

It sounds like you have a blockage in you air lines. The parking brake will automatically apply if it has no air to it. So what I would do is track down the air lines that go to the parking brake and then let the truck build up to about 30-50 psi and shut it down. Then get back under the truck and start cracking air lines to see if you have air pressure at the brake. If not move up the line till you find where your blockage is.

 

[Artisan]

With all due respect;

I highly recommend you get the TM's and start reading. Additionally you will
learn massive amounts of info if you go to a school like DOOTSON and get
a Class B CDL. You do know you need a Class B w/ Air brake endorsement
to drive that truck legally right? I suspect there is nothing wrong w/ your truck.
I could be wrong but..................you don't know what a gladhand is and
THAT tells me a lot, and frankly it scares me. You have not done any PMCS
have you? What was the results of your COLA test before you drove it
for the first time?


PS, if you are worth anything at all, and you get in a wreck and you do not
have a Class B CDL w/ Air brake license everything you have ever worked
for could be up for grabs in a court of law. It's called negligence. A harsh
word indeed but the law is the law.


In pilot lingo;

Your flying w/o being checked out in that aircraft by a certified instructor.
You can't jump from a PA28161 left seat and into a King Air left seat w/o proper training
or bad things can, and probably will happen. Sure, you might be able to take off
but not knowing what the lever w/ the round wheel looking thing on the end
is for and you fiddle w/ it could be a disaster coming home.

These trucks are tactical vehicles designed for warriors to use in harsh conditions.
They are unforgiving in the wrong hands. Please get proper training my friend.

The info you get on this board could be WRONG. Moi inclusive.

 

[Artisan]

It sounds like you have a blockage in you air lines. The parking brake will automatically apply if it has no air to it. So what I would do is track down the air lines that go to the parking brake and then let the truck build up to about 30-50 psi and shut it down. Then get back under the truck and start cracking air lines to see if you have air pressure at the brake. If not move up the line till you find where your blockage is.

Or someone fiddled w/ the isolation valves... or or or.

 

[maxtor]

With all due respect;

I highly recommend you get the TM's and start reading. Additionally you will
learn massive amounts of info if you go to a school like DOOTSON and get
a Class B CDL. You do know you need a Class B w/ Air brake endorsement
to drive that truck legally right? I suspect there is nothing wrong w/ your truck.
I could be wrong but..................you don't know what a gladhand is and
THAT tells me a lot, and frankly it scares me. You have not done any PMCS
have you? What was the results of your COLA test before you drove it
for the first time?


PS, if you are worth anything at all, and you get in a wreck and you do not
have a Class B CDL w/ Air brake license everything you have ever worked
for could be up for grabs in a court of law. It's called negligence. A harsh
word indeed but the law is the law.


In pilot lingo;

Your flying w/o being checked out in that aircraft by a certified instructor.
You can't jump from a PA28161 left seat and into a King Air left seat w/o proper training
or bad things can, and probably will happen. Sure, you might be able to take off
but not knowing what the lever w/ the round wheel looking thing on the end
is for and you fiddle w/ it could be a disaster coming home.

These trucks are tactical vehicles designed for warriors to use in harsh conditions.
They are unforgiving in the wrong hands. Please get proper training my friend.

The info you get on this board could be WRONG. Moi inclusive.

First of all, I have not driven this truck on the street. I have it on our property. Your sarcasm is not appreciated.
Before you show your ignorance on a another persons situation, I suggest you ask before you write.

If you would have read my posts, you will see I am here for information, and I have searched on the TM's. I am sure that if you were to want to learn to fly or build a computer network, you would be treated more civilly by me.

 

[maxtor]

5tonman1971
Sounds like a good plan. There is information on TM9-2320-272-24-1.pdf page 269-273 on parking brake malfunctions. I will do some trouble shooting tomorrow. Once I locate the cause of the problem I will post it.
Thank you for your help.

 

[Artisan]

My "help", and reply stands firm. Sarcasm, perhaps, incivility, not one ounce.
Please reread the very first line...Good luck.

 

[Floridianson]

I realy don't think you will find a blocked air line but the relay valves for the parking brake are in the side pannel drivers side step. The tank that supplys the air to the parking brake handel is the one under the drivers door. I might start with the compressor line and where it goes first then work along that supply line. The tanks not holding much air has me thinking about the Pressure protection valve but your not haveing any over pressure on the wet tank. Do both air gages show full pressure?

 

[Coffey1]

Yes 120 both gages

 

[Floridianson]

There was the thread where the roller valve on the parking brake handel was not returning down.

 

[Coffey1]

Checked that. The spring brake valve is either not getting air or not letting air through it.

 

[maxtor]

Yes, both gauges show approximately 125 psi. at full pressure.
We are forecast for seven days of rain, which we need desperately here in a drought stricken California, so I probably will not be able to start diagnosing the problem until after the rains stop.
I have about two miles on the truck, since delivery, but before this problem everything except the ctis worked fine. I really don't know if the ctis works or not, but the lights blink, so I will need to check that out later. One of the TM's suggests of resetting the CTIS, which I will do later on.
Right now, the locked brake problem is more important.
Thank you for your input. It gives me a place to start looking.

As Ken said, the next step is to open the three air lines to the spring brake valve, and start up the truck and see if air is getting to that valve. If air is getting to the valve, then possibly have a stuck or bad valve.
Thanks again Ken for all your help.

 

[Floridianson]

I might start at the air line at the parking brake. In the pic the first one closes to the back of cab is supply. The outher two I don't know when they feed as in parking brake up or down.

 

[maxtor]

In the TM's , it looks like line #5 is the air source to the spring brake valve. Your picture is different than what our setup looks like. It is raining now, so it will be awhile before I go out to do some trouble shooting.
Thanks again.

 

[Coffey1]

Max anytime bud. Glad to help. We have been going thru TMs if any TM guru's see something we are not seeing please speak up.

 

[Floridianson]

The one with the brass fitting is my supply line the T is for the air ride seat.

 

[maxtor]

The one with the brass fitting is my supply line the T is for the air ride seat.

I think that line is #5

 

[Floridianson]

Maybe the valve in the roller valve on the brake handel is sticking. I still might start there to see if you have supply in the one line and when you work the roller valve with your hand it should switch from one line to the outher line.