lmtv air brake leak

[man]

Hey guys! This is my first time posting. I hope that I'm doing it right.... Anyway, I have an LMTV that has a loud air leak suddenly coming from a relief valve behind the front air tank. It doesn't do it until I release the parking brake. The front brakes then begin to drag and sometimes lock up. What is this valve for? What is it called? And, what could be going on for it to be releasing air? It has a spring loaded diaphragm that appears to be doing what it is supposed to do. But, why is it being "called into action"?? Thanks, Man

 

[coachgeo]

Hey guys! This is my first time posting. I hope that I'm doing it right.... Anyway, I have an LMTV that has a loud air leak suddenly coming from a relief valve behind the front air tank. It doesn't do it until I release the parking brake. The front brakes then begin to drag and sometimes lock up. What is this valve for? What is it called? And, what could be going on for it to be releasing air? It has a spring loaded diaphragm that appears to be doing what it is supposed to do. But, why is it being "called into action"?? Thanks, Man

search this fmtv forum for ( "behind bumper" valve ) use the quotes. this might lead you to a fair list of search results for the many discussions on the valves behind the bumper. This will get you started. Post up questions you still need answers too inside one of those threads that are most appropriate to the subject..... If none fit well enough to sorta be on topic of course then start a new thread.

Glad to have you here. The more the merrier.

 

[tennmogger]

Man, you said "loud air leak suddenly coming from a relief valve behind the front air tank", so I'm curious where "behind the front bumper" came from. I am going to assume you meant behind the air tanks. That device behind the wet air tank is an over pressure valve. Is that it in the really poor photo I took a few minutes ago? Its purpose is to hold back air supply from 'secondary' circuits to insure that primary circuits, like brakes, are supplied first.

That device can leak, as mine has. It should never allow air out to atmosphere, only into the tubing beyond the device.

You can take it apart to be sure the diaphragm is good, and seal the edges of the diaphragm when you put it back together. RTV works, but needs to dry before it will hold pressure.

Is that the device to which you were referring, left center in the photo?

 

[man]

Thank you so much for chiming in! I've been pouring over the forums and the TMs trying to figure this out but I can't find any mention of this valve. Unfortunately, the valve in your pic isn't the one. My leaky valve is right behind the front tank. You have to crawl under the truck and look behind the tank to see it. It probably has a diaphragm much like all the other valves that may need changed but I need to make sure I know what I'm dealing with before I dig into it. Thanks!

 

[man]

When I say "behind the front air tank", I mean towards the center of the truck. I can post a pic tonight when I get off of work. Thanks again.

 

[man]

This is the valve on the front air tank.

 

[Smike740]

Here is a screenshot of the parts TM, looks like a check valve as well as whats being called a plug valve. I have replaced check valves and they are commonly available, never checked into a plug valve but i suspect it is available. Usually can be found at NAPA, truck parts stores and online.

 

[man]

That helps a lot. Thanks!!

 

[Smike740]

Did some more digging, the valve is made by bendix and its called an inversion valve and as you mentioned it is part of the parking brake system. Here is some more info.

 

[man]

Thanks for your time! The diagram shows an o-ring around the main plunger. I'll bet that's the problem. I'll open it this weekend and see if I can figure it out. Thanks again!

 

[coachgeo]

search this fmtv forum for ( "behind bumper" valve ) use the quotes. this might lead you to a fair list of search results for the many discussions on the valves behind the bumper. This will get you started. Post up questions you still need answers too inside one of those threads that are most appropriate to the subject..... If none fit well enough to sorta be on topic of course then start a new thread.

Glad to have you here. The more the merrier.

(eggs hitting and cracking over my head)smack/crack... splat/crack..... gooey flubble dripp... and (embarrassed) "oh".... "behind TANK" "could of swore I read" .. "behind BUMPER"..... "really, I swear" "someone hacked the post and musta changed the words the other night" ...