hicrop10 Posted November 5, 2023 Share Posted November 5, 2023 What would you call this.It’s the valve that send the air back to the trailer to release the brakes. It’s located center of cab in the back. Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/ Share on other sites More sharing options...
h67st Posted November 5, 2023 Share Posted November 5, 2023 On the later trucks, it's called the tractor protection valve (Bendix TP-3). Maybe the older trucks it's just called a relay valve? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541446 Share on other sites More sharing options...
Joey Mack Posted November 5, 2023 Share Posted November 5, 2023 are there any numbers cast into it? I have a Sealco book. I can try to get a part number.. It looks like and older version of what we call a QR-1 valve... (quick release) Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541447 Share on other sites More sharing options...
hicrop10 Posted November 5, 2023 Author Share Posted November 5, 2023 h67st,that’s what it known as.Found it on Fleet Pride site local store has 2 will be there Monday morning.Tks 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541450 Share on other sites More sharing options...
Freightrain Posted November 5, 2023 Share Posted November 5, 2023 Tractor protection valve. Uses TP1 on the dash to activate (if I recall correctly). The one on my B was only available as a rebuild. Had a buddy give me one out of his parts supply bin. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541456 Share on other sites More sharing options...
Licensed to kill Posted November 5, 2023 Share Posted November 5, 2023 Are those prone to failure?. When they fail, what goes wrong, IOW what gets replaced during a rebuild?. In wouldn't expect much in there but maybe a spring or two and some sort of valve/plunger that the spring moves. Of course this is just spec as I have no idea how it actually works. Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541463 Share on other sites More sharing options...
Geoff Weeks Posted November 5, 2023 Share Posted November 5, 2023 (edited) HOLD on, what year truck are you working on? Is it pre -121? It could be a TP-1 (not sure, never seen one, as they were out of production long before anything I had). TP-1's and TP-2's are out of production and even rebuilds are NLA as far as I know except for N.O.S. There is a TP that does look similar but is newer and has a double check function built into it. TP-3's and later (post -121) valves all function different than the pre-121 and are not directly compatible. If your supplier went off looks alone, it is very doubtful he will get the right part. It is VERY important to get the right valve TP-1 and -2 have the trip function (air pressure trip to close the valve) in the TP valve itself. The supply side is ALWAYS connected to tractor air at all times. The later TP-3's and up the trip function is in the dash button, and supply air goes through the dash button to the TP, which then opens, anytime it see's air pressure on the supply line. A TP-3 has four connections a TP-1 or 2 has five. There is a later TP that also has five, but has two supply lines, and a double check in it. That valve looks similar to a TP-1,or-2 but functions different. We need to know what you are working on and preferably numbers off the valve to be sure. edit: Whoops, I missed the title (I'm going to blame on the time change!) and see it is post -121! I found some pictures on line that look like it. It is a Midland TP valve. The top connection threw me because Bendix early valves are like that. I didn't see many Midland valves in my work. More info and pictures would help. The above mention of TP-1's got me on the wrong track. PS early (pre -121) are sometimes called "3 line system" and later (post -121) are called "2 line". Edited November 5, 2023 by Geoff Weeks Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541464 Share on other sites More sharing options...
Geoff Weeks Posted November 5, 2023 Share Posted November 5, 2023 1 hour ago, Licensed to kill said: Are those prone to failure?. When they fail, what goes wrong, IOW what gets replaced during a rebuild?. In wouldn't expect much in there but maybe a spring or two and some sort of valve/plunger that the spring moves. Of course this is just spec as I have no idea how it actually works. Most common failure is leaking out the exhaust, either with the valve open or closed, next common failure is leaks to the trailer side with the valve closed. Whether a rebuild kit will solve the problem depends on the state of the casting. Sometimes where the valves seat get worn/corroded and a "kit" will not solve that. Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541466 Share on other sites More sharing options...
hicrop10 Posted November 5, 2023 Author Share Posted November 5, 2023 I am working on a 1979 r model.I believe I need a tp3. Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541471 Share on other sites More sharing options...
Swishy Posted November 5, 2023 Share Posted November 5, 2023 (edited) Midland - Haldex V: https://class8truckparts.com/haldex-midland-tractor-protection-valve-kn34060.html cya Edited November 5, 2023 by Swishy 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73501-79-r-model-trailer-air-valve/#findComment-541477 Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.