LMTV Park Brake not working

mark1080 · May 16, 2015

On my LMTV 1099 The park brake doesn't work. Im not sure whats wrong because the regular brakes work just fine. regardless of weather you press to release or pull to apply, the park brake doesn't engage and the vehicle will role. Any thoughts? Also park brakes don't engage with lack of air pressure.

NDT · May 16, 2015

Silly question, your brakes aren't still caged are they?

mark1080 · May 16, 2015

What do you mean by "still caged"?

NDT · May 16, 2015

Often GP, DRMO, or the unit turning in the vehicle will cage the brakes so they can tow it.

Suprman · May 16, 2015

Post pic of brake chamber end.

mark1080 · May 16, 2015

Here are some pics. Caged brakes seems like the most likely thing I am dealing with. How does one go about caging and uncaging brakes?

Suprman · May 16, 2015

Nope not caged. The triangle plug comes out and a bolt would go in.

mark1080 · May 16, 2015

the regular brakes work great and the brake pads seem to still have a lot of life. any other ideas?

PowerstrokeNC · May 16, 2015

mark1080 said:
On my LMTV 1099 The park brake doesn't work. Im not sure whats wrong because the regular brakes work just fine. regardless of weather you press to release or pull to apply, the park brake doesn't engage and the vehicle will role. Any thoughts?

Are the rear brakes perhaps caged? Do you hear air release when you apply park brake?

NDT · May 16, 2015

I'm stumped sorry. This I don't understand: "Also park brakes don't apply with lack of air pressure". What on earth is holding the spring brakes back? Not a caging bolt, we see that. How could ALL 4 rear cans have frozen wedges? That is the only plausible explanation. Have someone actuate the brakes from the cab while you watch to see if the shoes move out to the drum on the rear. If the shoes do not move, you have front brakes only and your rear brakes need to be disassembled and freed up.

1951M1078 · May 17, 2015

Would the "driving rear brakes" still work if the wadge was frozen on the parking brake ? Sorry just a learning question.

Shark Bait · May 17, 2015

Are the release valves on the dash possibly switched? Truck valve switched with trailer valve? Truck should be on bottom and trailer on top. I believe. Lol. Just drove mine yesterday, I'm gettin old. If you drain the air tanks will it stay then?

mark1080 · May 17, 2015

NDT said:
I'm stumped sorry. This I don't understand: "Also park brakes don't apply with lack of air pressure". What on earth is holding the spring brakes back? Not a caging bolt, we see that. How could ALL 4 rear cans have frozen wedges? That is the only plausible explanation. Have someone actuate the brakes from the cab while you watch to see if the shoes move out to the drum on the rear. If the shoes do not move, you have front brakes only and your rear brakes need to be disassembled and freed up.

I have not checked which brake pads move when the brake is actuated. I will have to do that today. That will at least shed some more light on what is happening. Thanks

Suprman · May 17, 2015

With air completely drained from the system if the spring brakes still don't lock down and hold the truck there is something really weird going on. At that point I would bring it to a professional. I don't mess with spring brakes myself.

DSD277 · May 17, 2015

My guesstimate would be someone not familiar with air brakes and caging went in and backed out the adjusters to the shoes as to disable the brakes (rear service AND parking).
Personally, I'd put the caging bolts in, but not tighten them. Then air the system to see if the bolts retract (extend further out of the chamber) with the park system released. This would tell you if the activating rods are moving as they should.

Air brakes are a fail safe system and if anything goes wrong, the truck stops. UNLESS, there in some human intervention, usually not smart. :roll:

73m819 · May 17, 2015

With the truck stopping like it should tells that the wedge brakes are not frozen, if the spring pots are not getting air, the brakes "SHOULD" set, it almost sounds like the spring pots are getting air 100% of the time, it is against ALL odds that the springs broke in all the pots, just a guess, I think the ctis air got plumbed into the spring brake air system some where instead of a axle (look at the rear axle plumbing)., this is about the only way the spring brake pots will stay charged.

DSD277 · May 17, 2015

The park system circuit doesn't apply to the front axle, so truck could be stopping with front brakes only. Also, has the ip tried to release all the air from all the air tanks? That would be the acid test to whether it is a mechanical or air problem. With the system exhausted of all air, the fronts should lock up too, since it takes air for the brakes to release

Also is it a typo of LMTV 1099? did you mean 1079?

Suprman · May 17, 2015

The front brakes are usually only service brakes no springs to clamp down without air

DSD277 · May 17, 2015

Weak brain moment for me there. If they locked, they'd need to be caged too . :doh:

Exhausting all air still good... but I'll stick by my first guessimate. and backed out adjusters :tin hat:

73m819 · May 18, 2015

WHY ???? back off the adjusters, that WILL make things WORSE. if anything TAKE up the adjusters.

LMTV Park Brake not working

New member

Well-known member

New member

Well-known member

Well-known member

New member

Attachments

Well-known member

New member

New member

Well-known member

Well-known member

Active member

New member

Well-known member

Member

Rock = older than dirt , GA. MAFIA , Dirty

Member

Well-known member

Member

Rock = older than dirt , GA. MAFIA , Dirty