LMTV air/brake problems

[Overdrive]

Hope I am not late to the party on the issues described here...

I did the switchover on the park/trailer valves to the single Haldex unit and am interested in your issue with holding down the park valve for it to "stay put." Based on what I think I read, if your truck is venting out of the exhaust port behind the grill in front of the radiator and you are having air leak by the yellow park knob my first guess would be you installed one of the air lines incorrectly on the two valves (park/trailer). That exhaust port is only connected to the brake pedal and the two park/trailer valves so if your getting air out of there on startup something in those two systems is amiss. Mine did almost the same thing when I switched to the new single valve and didn't have one of the air supply lines hooked up properly. At the time it looked like I had a bad valve and would vent out the exhaust port on startup until I pressed in, released the park valve then it would build up to full pressure.

However, with the other issue being the brake pedal valve needing rebuild it would also vent to the same exhaust port... just to make my post a bit worthless

I have a write up on my upgrade to the single valve but it also shows a little crappy diagram of how my two valves were plumbed.


Just a thought for that particular issue.

OD


OD

 

[RAJ LMTV]

Sorry I didn't see you post earlier. Just got back to the forum today, thanks for the reply though. It would be nice if it were just a plumbing issue, I guess somewhere along the line someone could have jacked it up. I replaced both the park valve and the trailer valve and definitely reconnected everything the way I found it.
Where can I find the diagram that shows the correct connections?
Thanks

 

[RAJ LMTV]

Thanks to Overdrive for the diagram and picture of the valves. I definitely do have a configuration problem with my air lines. There was only one line connected between the two valves and from the info from Overdrive it looks like there should be three lines between the two valves. I dont really understand how to read the TM's about how everything should be plumbed. Does anyone else have an actual picture of the 2 valves that would show exactly where the lines should be hooked up between the 2? The one Overdrive posted is helpful but I can't really see exactly where they should go. Thanks

 

[coachgeo]

Looks complicated but I bet with a relaxed eye and a piece of paper drawing it out you can figure it out

 

[mkcoen]

RAJ - glad to see you're making some progress. Get it ready for Mullins in Oct!

 

[RAJ LMTV]

Hoping to to make it there for sure......everything else seems basically ready to go if I can just to get this brake issue taken care of

RAJ - glad to see you're making some progress. Get it ready for Mullins in Oct!

 

[RAJ LMTV]

Problem resolved! Took Overdrive's diagram along with the TM's diagram of the 2 valves and was able to finally sort it all out
That's a lot of air lines and at first look it seems overwhelming. Anyway with a proper configuration it's amazing how well everything functions. Previously I had nothing working with the trailer valve, now it works like it is supposed to and supplies air to the rear glad hand when activated. On a side note, I thought I had a problem with the air assist hydraulic unit as it would only lift the cab about 5" previously. Well that problem has now gone away also with the proper setup. Obviously (now) the unit wasn't getting the proper air flow since the plumbing was messed up but the cab lifts like a champ now. Thanks again to Overdrive for pointing me to the drawing. I took the truck out and made a quick trip around the block since I'm not exactly legal yet. Really the first time I have driven it. Seemed to run perfectly, brakes functioned properly, and got a lot of stares from people in their yards and driveways LOL. Waiting on a few misc parts to arrive then on to registering and getting street legal. Truck's going to be a fun ride.

 

[Oxyacetylene]

Problem resolved! Took Overdrive's diagram along with the TM's diagram of the 2 valves and was able to finally sort it all out
That's a lot of air lines and at first look it seems overwhelming. Anyway with a proper configuration it's amazing how well everything functions. Previously I had nothing working with the trailer valve, now it works like it is supposed to and supplies air to the rear glad hand when activated. On a side note, I thought I had a problem with the air assist hydraulic unit as it would only lift the cab about 5" previously. Well that problem has now gone away also with the proper setup. Obviously (now) the unit wasn't getting the proper air flow since the plumbing was messed up but the cab lifts like a champ now. Thanks again to Overdrive for pointing me to the drawing. I took the truck out and made a quick trip around the block since I'm not exactly legal yet. Really the first time I have driven it. Seemed to run perfectly, brakes functioned properly, and got a lot of stares from people in their yards and driveways LOL. Waiting on a few misc parts to arrive then on to registering and getting street legal. Truck's going to be a fun ride.

That's a good feeling isn't it? I know you are happy to have the truck in running order!

 

[FloridaAKM]

I spent Father's Day changing out the air brake shuttle valves under the Drivers side with new ones as the truck would not build air past 60 psi on the rear brakes & 0 on the front brakes. After knocking off all the mud dabber nests, I found a loose bolt(backed out 1/4") on the injector pump plate that was leaking oil on the heat exchanger under it, tightened it back up. Back to the shuttle valves, they all were trashed on the diaphram side of things, completely blown thru. So after restarting the engine, the compressor would build 90 psi on the rear brakes & 120 on the front brakes.The front brake guage would jump from 0 to pegged 120+ at about the time the rear guage would show 80 psi. The time after starting for the air to build is way too long! After shutting off the truck, there was major leakage @ the rear gladhands & the tractor protection valve. Since I have the rebuild kit from Haldex, that is the next item to rebuild when time permits! Its a work in progress that takes time for me to get done. Getting old is not fun!

 

[mkcoen]

Getting old is not fun!

I enjoyed the journey just not the destination

 

[FloridaAKM]

I thank the Lord every day for letting me have another one on this side of the grass, my brother after me died in 1988 @ 30 from brain cancer.......

 

[mkcoen]

I thank the Lord every day for letting me have another one on this side of the grass, my brother after me died in 1988 @ 30 from brain cancer.......

I'm right there with you. I was diagnosed with MS 13 years ago and thank the Lord every day that I can still walk and drive.

 

[Overdrive]

RAJ LMTV,
Awesome! I am really glad my post helped you figure the valves out.
OD

 

[RAJ LMTV]

Are these new problems with your air brake system or is this a truck you are working on to get it in shape?

I spent Father's Day changing out the air brake shuttle valves under the Drivers side with new ones as the truck would not build air past 60 psi on the rear brakes & 0 on the front brakes. After knocking off all the mud dabber nests, I found a loose bolt(backed out 1/4") on the injector pump plate that was leaking oil on the heat exchanger under it, tightened it back up. Back to the shuttle valves, they all were trashed on the diaphram side of things, completely blown thru. So after restarting the engine, the compressor would build 90 psi on the rear brakes & 120 on the front brakes.The front brake guage would jump from 0 to pegged 120+ at about the time the rear guage would show 80 psi. The time after starting for the air to build is way too long! After shutting off the truck, there was major leakage @ the rear gladhands & the tractor protection valve. Since I have the rebuild kit from Haldex, that is the next item to rebuild when time permits! Its a work in progress that takes time for me to get done. Getting old is not fun!

 

[FloridaAKM]

As I go thru the truck doing PM's, more things are cropping up that have to be fixed. The front shuttle valves wouldn't let air get past them due to the diaphragms being blown out. Now that the shuttle valves are working as designed, the components down the line are showing up as defective. Thanks to the guys here who know what to do, things are getting sorted out slowly. When I get her running, I'll know more about it than if it was a buy it & drive it deal! Anyway, still waiting on the title from GovPlanet!

 

[tennmogger]

Did anyone find the Wabco part number for the M-1078 treadle valve repair kit? I think the whole assembly is [h=3]WABCO 461 315 161 0 , but I want the rebuild kit. I don't find it anywhere on the FMTV forum even though there are many
references to the treadle valve.[/h]
Mine is leaking and I'm a long way from home. Disassembly, cleaning, and reassembly got it working for a short time but it is leaking slightly again. Nothing looks bad but next time I go into it I want to replace parts!!

Thanks!

4613151610

 

[tennmogger]

Haven't found info on a rebuild kit for Wabco 461-315-161-0 treadle valve yet. Several local auto parts places and a big truck repair place don't find reference to any kit. The big-trucks guy speculated the treadle valve is critical enough that a new, certified, valve might be all that is available.

Anyway, I took apart the treadle valve again, cleaned again, and got it working fine. The guts look like new, o-rings pliable, and face seals just fine. I had just found a tiny pile of sand in there and one chunk caught in a face seal. That's what dumped my air.

Here are some notes if you suspect trouble with the treadle valve. First, the vent for it is in the center of the front of the truck, in front of the radiator, and you can reach it if you take off the grill and reach upward. It vents downward. But, reaching it won't help a bit!

Physically tracing the source of the hose to that 'leak' is impossible....can't to it, it's back behind the heater. Just know that that vent comes from the treadle valve. The hose to the vent comes off the treadle valve on it's rear, the side nearest the driver, and nearest to the steering column. The thin-walled vent hose is a press fit, and can be removed by hand. Pull the hose off and now the vent is right there under the steering column where you can hear it. If you heard air escaping up front, you will heard it there at the treadle valve.

This is where the swoosh of air comes from when the brakes are dumped.

A leak through the treadle manifests as air coming out that vent. As air flows there then air will be flowing through the brake controller on the dash. It can sound like the (yellow knobbed) control is leaking.

The leak can be on either of the two circuits, front or rear, and it can make a huge difference on repair effort as to which is leaking. My initial leak was on the rearward section and that is the tough one to work on, but it can be done without removal.

Testing which section is leaking: First, a numbering convention is needed. There are four tubes coming out the left side of the treadle valve. As you look at them from standing beside the drivers floorboard, I called them 1, 2, 3, 4, just as read from top left to lower right.

1 and 2 are input hoses and have truck air on them. If you remove the lower two, 3 and 4, those go to the brakes and have zero pressure if not actuated. If pressure is coming out of either of those hoses (hose side) it's feedback from the brake system, and something leaking elsewhere, not the treadle.

If there's air coming out of the ports 3 or 4 then the treadle valve is leaking. My initial failure was air leaking out of port 3 (caused by the gravel in the face seal). My second failure was leakage coming out of port 4, the other face valve leaking.

If your leak is out number 4 then removal of just the most accessible half of the treadle valve is required. Disconnect the pressure sensor, take out 4 bolts holding the two halves of the treadle valve together, and work it loose. Note o-ring seal.

Take apart this half of the assembly with retainer clip pliers, being ready for strong spring pressure(!!!). Disassemble, clean out junk, lube, and reassemble.

It's a good idea to remove both hoses 1 and 2, build truck air, and let those hoses blow all the crud out of the lines before reattaching everything.

That how I got my brakes going.

 

[Suprman]

There is a check valve behind the passenger side bumper that is part of the brake air release. I have heard of that check valve sticking and causing brake issues.

 

[Overdrive]

Be aware that the Park/Trailer valves also "VENT" out the same port behind the grill, in front of the radiator as the treadle valve.



OD

 

[tennmogger]

Great picture! So THAT's what the vent looks like on top!