Air Fails To Build Intermittently; Parking Brake?

gottaluvit · Jul 4, 2015

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?

porkysplace · Jul 4, 2015

Start with rebuilding or replacing the the air dryer ( normal maintainence).

gottaluvit · Jul 4, 2015

Thanks. I just did replace it with an mrap one last week. Had unloader valve stuck and fixed that too.

Ford Mechanic · Jul 4, 2015

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

gottaluvit · Jul 5, 2015

Ford Mechanic said:
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

Excellent plan. Will do that later today. Thank you.

lindsey97 · Jul 5, 2015

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.

gottaluvit · Jul 5, 2015

lindsey97 said:
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.

A new governor sure would be a good idea being they are fairly cheap. Where is this tractor protection valve at?

The HUlk · Jul 5, 2015

gottaluvit said:
A new governor sure would be a good idea being they are fairly cheap. Where is this tractor protection valve at?

The PPV valve is located on the front bottom side of the wet air tank. It looks like an adjustable valve with a round handle on one end.

I just got done solving some air problems, you may want to have a look at this if you haven't seen it:

http://www.steelsoldiers.com/showthread.php?141256-M939-Inconsistent-air-pressure

gottaluvit · Jul 5, 2015

The HUlk said:
The PPV valve is located on the front bottom side of the wet air tank. It looks like an adjustable valve with a round handle on one end.

I just got done solving some air problems, you may want to have a look at this if you haven't seen it:

http://www.steelsoldiers.com/showthread.php?141256-M939-Inconsistent-air-pressure

Thank you. I will study that thread this evening.

gottaluvit · Jul 5, 2015

Couldn't wait to read this as I will after all have some time today to work on the truck. Looks like this is my issue but will know for sure in a few hours. Thanks again.

Jim

lindsey97 · Jul 5, 2015

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 · Jul 5, 2015

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 · Jul 5, 2015

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 · Jul 5, 2015

lindsey97 said:
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 · Jul 5, 2015

lindsey97 said:
View attachment 568482 View 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 · Jul 5, 2015

lindsey97 said:
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 · Jul 5, 2015

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 · Jul 5, 2015

Excellent. Thanks. I will call the big rig dealer in wheeling tomorrow and order one.

juanprado · Jul 5, 2015

OE bendix pr2 pressure protection valve 277147 65psi 1/4 ports or equivalent. NAPA or any HD truck parts

http://epi.hbsna.com/products/dept....4BE3BEBAD17D40131E2C&dept_id=1600&parent_id=0

gottaluvit · Jul 5, 2015

lindsey97 said:
View attachment 568482 View 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.

Air Fails To Build Intermittently; Parking Brake?

Well-known member

Well-known member

Well-known member

Active member

Well-known member

Member

Well-known member

Member

Well-known member

Well-known member

Member

Active member

Member

Well-known member

Well-known member

Well-known member

Active member

Well-known member

Well-known member

Well-known member