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Tractor Parking Valve


farmer52
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When I shutdown I can hear air leaking at the tractor parking valve (yellow knob). If I turn it or quickly push in/pull out it will sometimes stop.

Are these rebuildable or just replace? Does it make a difference which brand (Bendix, Haldex, etc.) I use for a replacement? How do I know what brand is installed now? BTW, the part number is 20QE2167. Thanks for any info.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Ken,the leaking is usually caused by a worn "O" ring behind the valve (not easily replaced,but not impossible) from being pushed/pulled over the years, better to change the whole valve (not a bad job at all) and personally i'd stick with whats there (brandwise) always had good luck with Bendix brake products..............................................Mark

I thought an o-ring is worn and causing the leak. I agree...replace. Is there a way to determine the manufacturer without "looking" at the valve? Is the Mack part number exclusive to a manufacturer? I am in OH this week and will not be able to put an eye on it until next week.

I sent a PM to Barry.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Stopped by Watt's this morning and picked up a new Bendix valve from Barry. I had the wrong part number, correct one is 20QE3219. Tomorrow I will pop the lid off the dash and make sure it is the same valve. Then do some wrenching and change it out.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Stopped by Watt's this morning and picked up a new Bendix valve from Barry. I had the wrong part number, correct one is 20QE3219. Tomorrow I will pop the lid off the dash and make sure it is the same valve. Then do some wrenching and change it out.

Changed out the valve this morning. No leaks at the valve or dash! :twothumbsup:

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Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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  • 2 weeks later...

When I bought my 85 I had to replace two of the three brake valves in the dash just to build enough pressure to load it on the trailer. I think they were like $30 ea from Mack and the new knobs were another $10 ea. Well worth it since they wear over time to just swap em out for $80 and not look at em again for another 27 years.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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The air is still leaking down over a few days. It seems the air leaks down quicker when the trailer lines are disconnected. I bought a TP (tractor protection) valve from Barry. I am going to replace the TPV and see if it helps prevent leakdown.

BTW, does anyone know what the Blue knob/valve does? I never use it, just the Yellow (without trailer) and both Yellow and Red with trailer.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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The yellow valve supplies air to both the the blue valve (tractor park) and red valve (trailer air supply).

This way way when you pull the yellow valve it sets all the brakes tractor and trailer just by pulling the one knob. (system park).

Once you push in the yellow knob then you can either release the tractor brakes with the blue or release (supply air) to the trailer with the red independent of each other.

Ron

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The yellow valve supplies air to both the the blue valve (tractor park) and red valve (trailer air supply).

This way way when you pull the yellow valve it sets all the brakes tractor and trailer just by pulling the one knob. (system park).

Once you push in the yellow knob then you can either release the tractor brakes with the blue or release (supply air) to the trailer with the red independent of each other.

Ron

Ron, thanks for the complete explanation. I knew about the yellow and red but I NEVER touch the BLUE valve even when bobtailing. So that is why I asked its purpose.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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The air is still leaking down over a few days. It seems the air leaks down quicker when the trailer lines are disconnected. I bought a TP (tractor protection) valve from Barry. I am going to replace the TPV and see if it helps prevent leakdown.

BTW, does anyone know what the Blue knob/valve does? I never use it, just the Yellow (without trailer) and both Yellow and Red with trailer.

If the truck holds air for a "few days" I wouldnt be chasing any more air leaks if it was me.

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If the truck holds air for a "few days" I wouldnt be chasing any more air leaks if it was me.

Yes, once I replace the TP valve I am going to stop chasing air leaks (unless I hear air leaking). Since I have a trailer, I usually keep the air lines connected. But when the lines are disconnected, the air leaks down within a matter of hours or overnight.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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As long as the trailer brakes are set ( red valve out) having the lines connected or not won't make a difference, the tractor protection valve is there to keep the truck from losing air pressure if the trailer gets a major leak. You can test the tpv by releasing the trailer brakes (push the red valve in) and remove the trailer emergency line (red line) air will rush out of the gladhand for a minute but at the set pressure the tpv will pop and close the trailer valve so you don't lose all the air in your tractor. If your truck is losing air at a rate less than the DOT standard just let it go unless its really bugging you. I'm surprised you dont use the tractor parking valve (the blue valve) its possible its been bypassed and you could have a leak there.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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As long as the trailer brakes are set ( red valve out) having the lines connected or not won't make a difference, the tractor protection valve is there to keep the truck from losing air pressure if the trailer gets a major leak. You can test the tpv by releasing the trailer brakes (push the red valve in) and remove the trailer emergency line (red line) air will rush out of the gladhand for a minute but at the set pressure the tpv will pop and close the trailer valve so you don't lose all the air in your tractor. If your truck is losing air at a rate less than the DOT standard just let it go unless its really bugging you. I'm surprised you dont use the tractor parking valve (the blue valve) its possible its been bypassed and you could have a leak there.

I think I tried using the blue valve and nothing happened. My guess is it is bypassed. I will take the dash cover off and take a look. I don't hear any air leaking since I replaced the TT valve (yellow knob).

Air definitely leaks down quicker with the trailer lines disconnected.

The test truck were I worked would hold air for weeks, it was a 2008 model.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Mine did great for a few years, my worst leak was air wiper switch. I think it needs a new o-ring again? It is annoying that it won't hold air over night(or even through an afternoon), but not worth chasing. After putting a new leveling valve on the air ride, it stays up for weeks, even if air is down on truck.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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  • 3 weeks later...

I replaced the tractor protection valve and air tank drain valves. While I was in the "mood" I replaced the trailer air lines and gladhands. The air does not leak down overnight like it did peviously. As I posted before, I am done "searching" for air leaks....unless I hear air leaking. On to the next item on my loonnnggg list.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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  • 1 month later...

I know you all some of you think I am being a fanatic about leaking air but....

Yesterday morning when I was getting ready to move the MH to winter storage....

Air pressure gauge showed green needle (secondary tank?) at 60 psi, the red needle (primary tank?) was 0 psi.

Any thoughts (be nice)?

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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primary or (wet tank ) check valve allowing air to excape through the compressor ? do you have a air dryer? pin hole in tank or lines? trans shift knob?internal trans air leak? wiper sw. valve heater controls ? Find neighbor kid with good ears that likes to get dirty and offer him 20 bucks to crawl all over that truck and look for the leak while you drink a beer !!!!!!!!!!!!!!!!!!!

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primary or (wet tank ) check valve allowing air to excape through the compressor ? do you have a air dryer? pin hole in tank or lines? trans shift knob?internal trans air leak? wiper sw. valve heater controls ? Find neighbor kid with good ears that likes to get dirty and offer him 20 bucks to crawl all over that truck and look for the leak while you drink a beer !!!!!!!!!!!!!!!!!!!

No air dryer, no trans shift knob (T2050), no internal trans air leak.

Check valve in the primary tank? Where is it located and can it be replaced?

I know....leave it alone and move on. :unsure:

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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