Won an LMTV M1081 out of Ft. Bragg

[scottmandu]

There is a relay valve attached to the parking brake system that requires the parking brake to be applied for the auxiliary hydraulics to work (cab tile spare tire etc). That valve could be your problem.. Also check the anti-compounding valve and inversion valve for the brakes. All can be replaced with new parts for about $300 bucks.

 

[scottmandu]

Is the treadle rebuildable?

Likely but I've been able to find aftermarket prices for all the brake parts at the local big truck shop. It's a Wabco part..

 

[jjb]

There is a relay valve attached to the parking brake system that requires the parking brake to be applied for the auxiliary hydraulics to work (cab tile spare tire etc). That valve could be your problem.. Also check the anti-compounding valve and inversion valve for the brakes. All can be replaced with new parts for about $300 bucks.

Any idea where the relay valve is?

 

[scottmandu]

Any idea where the relay valve is?

It's behind the air tanks. Just follow the feed line to the aux manifold to the tanks.

 

[jjb]

It's behind the air tanks. Just follow the feed line to the aux manifold to the tanks.

Is it the one with 2 Phillips head screws? Looks like a pressure regulator?

 

[Lmtv772]

The pedal seems fine and the brakes appear fine. Haven't checked them individually yet.

Is the treadle rebuildable?

Yes it is rebuildable and I have a spare kit from when I did mine

 

[jjb]

Yes it is rebuildable and I have a spare kit from when I did mine

Do you have the part number? Not sure I need it yet but good to have the number in case I do

 

[Lmtv772]

Do you have the part number? Not sure I need it yet but good to have the number in case I do

I can provide you with the kit I have

 

[jjb]

I can provide you with the kit I have

Ok, what do you want for it with shipping?

 

[jjb]

I took the inversion valve apart on the rear cross member and it seemed to be working. Next to it is a 2-way check valve. It have a badly kinked air line. When I took it apart it had a cracked diaphram. See attached picture.

Would this cause the parking brake to not function?

View attachment 613020

 

[jjb]

There is a relay valve attached to the parking brake system that requires the parking brake to be applied for the auxiliary hydraulics to work (cab tile spare tire etc). That valve could be your problem.. Also check the anti-compounding valve and inversion valve for the brakes. All can be replaced with new parts for about $300 bucks.

Is the relay valve you are referring to #24 in the first picture? They call that a plug valve in the parts TM but Bendix calls it and inversion valve. I attached a picture I found on ebay of the valve.

 

[jjb]

I just realized that the picture I tried posting of the bad two-way check valve didn't come up for some reason. Here goes again.

 

[Lmtv772]

I just realized that the picture I tried posting of the bad two-way check valve didn't come up for some reason. Here goes again.

View attachment 613229

That looks like one of the 3 membrane valves. I bought new shuttle valves and replaced the membrane valves completely. You can choose between

a diaphragm valve as in the LMTV KN25060
Repair kit for diaphragm valve RN11V
or a shuttle type valve as in the MTV KN25061
the shuttle valves are used in the later FMTV 2004 and up and have a much higher quality

​

 

[jjb]

That looks like one of the 3 membrane valves. I bought new shuttle valves and replaced the membrane valves completely. You can choose between

a diaphragm valve as in the LMTV KN25060
Repair kit for diaphragm valve RN11V
or a shuttle type valve as in the MTV KN25061
the shuttle valves are used in the later FMTV 2004 and up and have a much higher quality

​

From the TMs I have found 4 of them. This one on the rear cross member, one on the back of the air tanks and 2 under the cab. There may be others I haven't found yet.

 

[jjb]

That looks like one of the 3 membrane valves. I bought new shuttle valves and replaced the membrane valves completely. You can choose between

a diaphragm valve as in the LMTV KN25060
Repair kit for diaphragm valve RN11V
or a shuttle type valve as in the MTV KN25061
the shuttle valves are used in the later FMTV 2004 and up and have a much higher quality

​

Any idea if that bad diaphragm could cause the parking brake to not engage?

 

[Lmtv772]

Any idea if that bad diaphragm could cause the parking brake to not engage?

if it leaks enough for the pressure to be ~50lbs I can see it as the park brake valve needs pressure to stay engaged.

 

[Lmtv772]

From the TMs I have found 4 of them. This one on the rear cross member, one on the back of the air tanks and 2 under the cab. There may be others I haven't found yet.

there are 3 under the cab, driver side.

 

[jjb]

if it leaks enough for the pressure to be ~50lbs I can see it as the park brake valve needs pressure to stay engaged.

It releases fine. The parking brakes won't engage.

 

[Suprman]

Do the brakes hold the truck with all the air drained out no air in the system truck off?

 

[jjb]

Do the brakes hold the truck with all the air drained out no air in the system truck off?

Yes, and the service brakes seem to work fine. No major air leaks pressure is good.