New truck and a stuck brake! M923

[GeekOnAmission]

Hi guys, I am new to this site as well as the M923 I just bought. On my drive home my chase truck called and told me the rear axle was smoking. Upon inspection I found the right rear wheel's brake was stuck. I couldn't find anything obviously wrong and it seemed to stick after a somewhat hard brake to make a left turn, so I don't think it was like that at the beginning of the trip. I ended up caging the brakes for that wheel and driving her home to deal with it there.

The ABS light is always on, and the air system seems to be working correctly. All of the other wheels seem alright, and the primary and secondary tanks work the range from 90-120 depending on braking frequency. I drained the tanks when I got home and didn't see any water escaping that may have made it past the drier.

Any suggestions on where to start? Any help is appreciated. I am not entirely new to the 121 air systems, but it has been a couple years since I have even been near one, and have never worked on anything military except my M1009, which is pretty basic.

 

[Artisan]

I am no mechanic ...having said that If you install an air hose
fitting so that you can pump air into the system w/o the engine running
you have a way better chance of finding an air line leak.

Additionally have you done a C.O.L.A. test?

You prob have a bad air chamber diaphgram , JUST guessing.

I would volunteer to come over and help you out just to gain more
knowledge myself. My truck is 1200 miles away...I will be getting
another for the SGV HA!

 

[Danl]

Hi guys, I am new to this site as well as the M923 I just bought. On my drive home my chase truck called and told me the rear axle was smoking. Upon inspection I found the right rear wheel's brake was stuck. I couldn't find anything obviously wrong and it seemed to stick after a somewhat hard brake to make a left turn, so I don't think it was like that at the beginning of the trip. I ended up caging the brakes for that wheel and driving her home to deal with it there.

The ABS light is always on, and the air system seems to be working correctly. All of the other wheels seem alright, and the primary and secondary tanks work the range from 90-120 depending on braking frequency. I drained the tanks when I got home and didn't see any water escaping that may have made it past the drier.

Any suggestions on where to start? Any help is appreciated. I am not entirely new to the 121 air systems, but it has been a couple years since I have even been near one, and have never worked on anything military except my M1009, which is pretty basic.

I would Change the break can or rebuild it , the rubber dieofram is leaking by, a new can is cheap money,and quick to install. Than, take and rebuild the old can and you will always have a spear can on hand

 

[Danl]

I would Change the break can or rebuild it , the rubber dieofram is leaking by, a new can is cheap money,and quick to install. Than, take and rebuild the old can and you will always have a spear can on hand

Don't for get to grease the fitting, when was the last time the system saw Grease?

 

[swbradley1]

Before you get carried away and start following advice on replacing stuff how about looking at the TMs and adjust the breaks AFTER inspecting them.

Gimpy and I had the same thing on a 915 recovery and the problem was mis-adjusted brakes and nothing else.

Welcome to the site and enjoy the truck. The ABS is most likely the control box which are available.

 

[waayfast]

OK!! I am not familiar with the 923 series of trucks but do have lots of experience with large commercial trucks.

If (I assume they are) equipped with standard,modern air brakes, then release the park brake (push in knob on the dash).

Have someone listen at the corner in question--if there is air escaping out the aircan itself then you have a bad/leaking diaphram.

IF THE AIRCAN IS BAD-REPLACE IT. DO NOT, I REPEAT DO NOT TRY TO DISASSYMBLE THE AIRCAN TO REBUILD!!!!!!!!!!

THIS WILL KILL YOU!!!! The spring inside is under pressure and if you take the bail off that chamber it will pop out with great force and if you are (usually your FACE) is in the way you will have a VERY bad day.

Hope I have alarmed you ---I MEANT TO.

Jim

 

[drgreg]

There is no knob on the dash. I'd go with post #5, let us know what you find.

 

[GeekOnAmission]

Thanks guys, I'm gonna start simple and work from there. I'll start with the inspection and if we pass it I'll move to checking adjustment. I already listened to the brake during actuation and didn't hear any air or physical movement at the can, so I suspect it's a blocked line or valve somewhere up stream.

I'll report in tonight and let you know what I found. What's a good vendor for the abs box? Anyone know if the DLC is the same 6 or 9 pin Deutsch found on commercial trucks, or is a special scanner going to be needed?

 

[Nonotagain]

Lubricate the BRAKE wedges on all of the wheels with a good high temperature grease and adjust all of the brakes.

Most of these trucks sat for a long time before being sold off. If you had to apply the brakes hard, you may have pushed one of the wedges into a position that was heavily rusted and casued it to stick.

After you lubricate the wedges, If the brake can has a leak in a diaphram, you'll hear it with the engine off if you get someone to press and hold the pedal.

 

[rrrr]

As said before get into the TM's. I spent a huge amount of time in them before I started working on my 932. If you don't know how to cage a brake then you better spend time reading before you do anything. You will hurt yourself ! I replaced all 4 of my rear diaphragms trying to diagnose a problem, turned out two air lines were crossed ! It took me three days of work to finally correct the situation. Good luck and use the search function in the forum; this has been addressed many times. Let us know the outcome.

Enjoy the new toy !

 

[goldneagle]

There is no knob on the dash. I'd go with post #5, let us know what you find.

There is a large push-pull knob on the dash on the right side of the gauges. Push in to release spring breaks for testing. Leave the parking brake on. Go listen for air leaks.

 

[drgreg]

There is a large push-pull knob on the dash on the right side of the gauges. Push in to release spring breaks for testing. Leave the parking brake on. Go listen for air leaks.

"If (I assume they are) equipped with standard,modern air brakes, then release the park brake (push in knob on the dash)." Does yours have the knob described here? Mine doesn't.

 

[Farmallmilitary]

Just last week i had to replace a diaphragm on a service chamber. The service chamber was a piece of cake. I still need to get a new diaphragm on the spring brake side though. What i did was hook up a quick release air coupling where you can pressurize the system from shop air. The easiest place on the system i found where you can directly hook something up is on th passenger side. Its right behind the rear tool box at the "pressure release valve". Doing that it made it alot easier to diagnose the problems.

 

[RobM923]

another break question

I have a brake question (my truck is a M923) and not sure how to post it without starting a new thread (which somebody on this board suggested not to do). My first question is with the knob (Spring Brake Emergency Control), from what I've read this knob needs to be pulled out for driving the truck, thats how I've been using it because when I pull the knob out it turns the light (spring break over ride) off on my dash and the knob reads "PULL FOR NORMAL" and I'm assuming normal is driving.
The problem I am having (I've been pouring over the TM's to try to fix) is the following...When I get in the truck pressure up the brake system and put it in gear, the truck creeps forward if I take my foot off the brake (perfectly normal). The problem is that after I apply the brakes once or twice (just moving the truck around) my rear brakes stay engaged and the truck will no creep forward when my foot is off the brake, I have to vercome by giving it throttle. I have taken the dust covers off all the brakes and noticed that my two rear axles break pads (shoes) don't release off the drum when my foot is off the brake pedal. But, if I let the truck sit for a bit the brake pads release. Any ideas or can anyone direct me to the part of the TM that trouble shoots this problem. I've read where it may be the valves on the drivers side of the truck next to the step. It feels to me like there is a valve not releasing air pressure maybe dirty or stuck. Also, I have an external air source plugged into the truck, dont want to keep running my engine. Any advise will be greatly appreciated.

 

[RobM923]

More info. the brake system is aired up at the moment rear pads (shoes) are off the drums. Also , I noticed that my spring brake "knob" has no affect on the brakes, in or out the brake shoes don't move . Doesn't the Spring Brake Control knob release the air holding the rear brake springs back (compressed)? BTW, sorry, I just notice I've been misspelling brakes! I'm really not that stupid

 

[mudball]

I have a brake question (my truck is a M923) and not sure how to post it without starting a new thread (which somebody on this board suggested not to do). My first question is with the knob (Spring Brake Emergency Control), from what I've read this knob needs to be pulled out for driving the truck, thats how I've been using it because when I pull the knob out it turns the light (spring break over ride) off on my dash and the knob reads "PULL FOR NORMAL" and I'm assuming normal is driving.
The problem I am having (I've been pouring over the TM's to try to fix) is the following...When I get in the truck pressure up the brake system and put it in gear, the truck creeps forward if I take my foot off the brake (perfectly normal). The problem is that after I apply the brakes once or twice (just moving the truck around) my rear brakes stay engaged and the truck will no creep forward when my foot is off the brake, I have to vercome by giving it throttle. I have taken the dust covers off all the brakes and noticed that my two rear axles break pads (shoes) don't release off the drum when my foot is off the brake pedal. But, if I let the truck sit for a bit the brake pads release. Any ideas or can anyone direct me to the part of the TM that trouble shoots this problem. I've read where it may be the valves on the drivers side of the truck next to the step. It feels to me like there is a valve not releasing air pressure maybe dirty or stuck. Also, I have an external air source plugged into the truck, dont want to keep running my engine. Any advise will be greatly appreciated.[/

It sounds like a dump valve,or a vent line plugged. When you apply pressure, upon release of the pedal you should hear a rush of air as the system exhausts. I would assume that each axle has its own valve or both would be sluggish upon release,unless the front axle is way out of adjustment. I will try to look under my 923 to see where the valves are and what style they are.

 

[RobM923]

I hear air blowing out when I release the pedal but not sure if it's enough (don't have another truck for comparison). The brake shoes definately stay up against the drum and dont release, but after the truck sits for about 3-5 minutes the shoes release. Thats what makes me think it's a stuck or stiky air valve somewhere. I took all of the valves apart under the drivers side step, didn't see anything that stood out, they were a little dry but overall clean and seemed operable, I serviced them (cleaned and lubricated o rings0 and re assembled.

 

[Artisan]

If you start the truck and touch nothing letting it
run for maybe 5 minutes what does the primary and secondary
air pressure gauges read in PSI ?

 

[RobM923]

Both tanks pressure up they read somewhere between 110 and 120 psi (never took note exactly how many psi). Yesterday I noticed the spring brakes on the center axle are caged, not sure why. Today I plan on uncaging them and continuing to troubleshoot the brakes. Still havent found why my rear brakes (both axles) won't release when I take my foot off the brake pedal

 

[Artisan]

When you drain your air tanks, the 4 valves on the PS
do you get air out of all 4 ports?

Do you get air, high pressure out of the PS rear gladhand?

Are all gladhands valve or capped?

I am NO PRO by far FWIW. I would like to know what
you find ...