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Air Fails To Build Intermittently; Parking Brake?

gottaluvit

Well-known member
So I had the truck out for a 20 mile or so test drive yesterday. This is the longest drive I had taken with the truck to date. It started raining and I ran the wipers but after a few miles they just stopped. Looked at the gauges and they were around 50 psi. I pulled over and set the parking brake and noticed the pressure started building but failed to do so with the brake not set. After it aired up, I continued my way home to see it hold pretty good. So I went on past home to keep trying to figure out what may be the issue and the same happened twice more. Got it back home and drained the tanks.

So today I fire it up and all seemed normal. Went a couple miles and same thing started again. Messed with the parking brake air lever and could see it start building pressure as soon as I would pull up on the lever. I go down the road and it does it again (a couple times) but sometimes the parking brake lever has no effect. After getting it home with 40 psi (too close for comfort), I shut it off and drained the tanks. Then fired it back up and it built up normally to 122 psi.

Searches came close on here but nobody mentioned it working normally after draining tanks and making it start from empty tanks. Is there some check valve sticking?
 

Ford Mechanic

Active member
1,805
6
38
Location
Edenton, NC
With full pressure shut the engine down and then disengage the p-brake. Then check for any leaks under the truck. Like the cans or relay valves, expecially the circuit that don't have air pressure until the p-brake is disengaged
 

lindsey97

Member
738
16
18
Location
wynnewood, oklahoma
Chock the wheels first before performing the above mentioned task. A new air governor and checking your tractor protection valve for rust and being stopped up won't hurt either.
 

The HUlk

Member
469
7
18
Location
Cincy, OH

gottaluvit

Well-known member

lindsey97

Member
738
16
18
Location
wynnewood, oklahoma
I removed my tractor protection valve and threw it away. Cannot advise you to do the same for safety and liability reasons. Simple solution though. When the truck is acting up, and not making pressure, is it on the primary gauge and the secondary, or just the primary.

When the truck is acting up, do the windshield wipers work and have air pressure? If the wipers won't work, and the 2 air gauges read different pressures, it may very well be the tractor protection valve having rust/trash in it and not opening correctly to allow the secondary side of the air system to pressure up.
 

Ford Mechanic

Active member
1,805
6
38
Location
Edenton, NC
I had a ppv stick on my way back from the Denton rally, the symptoms were I lost all my secondary air functions. I.e. wipers, horn and CTIS. Air pressure was still correct and building correctly. It was raining at the time and my wipers just quit suddenly.
 

lindsey97

Member
738
16
18
Location
wynnewood, oklahoma
m923_ppv 002.jpgm923_ppv 001.jpg

M923 ppv located on right air tank on the end of it. my truck was functioning perfectly, then one day started making too much air, then not enough in the secondary side. I replaced the air dryer cartridge, then the air governor, and that helped, but still couldn't get the secondary to build air at the same rate as the primary. I also took apart the unloader and cleaned everything in it. Had a lot of carbon in the unloader.

The ppv only costs $25 and I would check it out for rust. It gave me fits, and I own a wheel loader with air brakes and 2 class 8 dump trucks with air brakes. As you can see, my ppv no longer resides on the truck.
 

gottaluvit

Well-known member
I removed my tractor protection valve and threw it away. Cannot advise you to do the same for safety and liability reasons. Simple solution though. When the truck is acting up, and not making pressure, is it on the primary gauge and the secondary, or just the primary.

When the truck is acting up, do the windshield wipers work and have air pressure? If the wipers won't work, and the 2 air gauges read different pressures, it may very well be the tractor protection valve having rust/trash in it and not opening correctly to allow the secondary side of the air system to pressure up.
The wipers did fail and I am having different pressures on the guages, when it is acting up. I wont bypass the valve but give it a good cleaning and run it and order a new one since they're so cheap. Any suggestions on sources?
 

gottaluvit

Well-known member
View attachment 568482View attachment 568483

M923 ppv located on right air tank on the end of it. my truck was functioning perfectly, then one day started making too much air, then not enough in the secondary side. I replaced the air dryer cartridge, then the air governor, and that helped, but still couldn't get the secondary to build air at the same rate as the primary. I also took apart the unloader and cleaned everything in it. Had a lot of carbon in the unloader.

The ppv only costs $25 and I would check it out for rust. It gave me fits, and I own a wheel loader with air brakes and 2 class 8 dump trucks with air brakes. As you can see, my ppv no longer resides on the truck.
Thanks for the pics. Now I know what I am looking for as well as where.
 

gottaluvit

Well-known member
I removed my tractor protection valve and threw it away. Cannot advise you to do the same for safety and liability reasons. Simple solution though. When the truck is acting up, and not making pressure, is it on the primary gauge and the secondary, or just the primary.

When the truck is acting up, do the windshield wipers work and have air pressure? If the wipers won't work, and the 2 air gauges read different pressures, it may very well be the tractor protection valve having rust/trash in it and not opening correctly to allow the secondary side of the air system to pressure up.
Mainly primary, but secondary follows suit about 40-50 psi behind.
 

Ford Mechanic

Active member
1,805
6
38
Location
Edenton, NC
I got mine from the local big truck parts store, Dixie Auto. I got the number from here on SS can't remember where. Maybe in the parts sticky at the top of this section.
 

gottaluvit

Well-known member
View attachment 568482View attachment 568483

M923 ppv located on right air tank on the end of it. my truck was functioning perfectly, then one day started making too much air, then not enough in the secondary side. I replaced the air dryer cartridge, then the air governor, and that helped, but still couldn't get the secondary to build air at the same rate as the primary. I also took apart the unloader and cleaned everything in it. Had a lot of carbon in the unloader.

The ppv only costs $25 and I would check it out for rust. It gave me fits, and I own a wheel loader with air brakes and 2 class 8 dump trucks with air brakes. As you can see, my ppv no longer resides on the truck.
Well, I just crawled under the truck and that valve is nowhere to be found. So is it supposed to be on the front of the wet tank? I actually looked at every air tank to be sure and cannot find a valve that looks near that anywhere.
 
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