M1078A0/ Parking Brake Release

[Lugnuts]

After reading my air line schematics available on Steel Soldiers and after going to YouTube to view RonMars Air Component Video (which by the way is excellent even after the 4th time) I am turn for help for confirmation.
My parking brakes are taking 20 seconds to fully release. I suspect it is the relay valve since the AntiCompound Valve is first to receive air and then to the Relay Valve/ that would mean that the first point of releasing air is at the Relay Valve.
I did replace both Trailer Valve and Parking Brake Valve because the were leaking air at the stems/ Not particularly a fun job because of the close quarters but done.
The symptoms I have is when Parking brake valve is pushed in calling for release of parking brakes all works well if I apply and drive/ When they are pushed to release and then popped off and then attempt to push right back in it is as hard as a rock and can only be pushed back in and set when held. Now when normally the Parking Brake Valve is pulled out to set the Parking Brakes all works well providing you wait 20 seconds. I have popped the valve and run to the back and felt that air is seeping out of the relay and then at the end of 20 seconds it completes exhaust with a sort of swoosh/
Would it be recommended to pull each line going to the chambers and using shop air apply and release to see if maybe I have a chamber hanging up. (Now that I say it that sounds about right) Or is it most commonly the Relay Valve? I didn't have the help to see if one side releases and not the other or if it is an equal release.
All input is appreciated! By the way does anyone have the Relay Valve number or the Military Number on the Parking Brake Relay Valve which I suspect is the same as the Service Valve Relay. OH RonMar where are you???

 

[Ronmar]

The anticompound is the only component that controls air to the park spring chambers.
It is a relay valve, much like the service brake relay right below it on the crossmember.

It differs from the service relay in that it has a 2way check valve built into its input, so can accept two different inputs, park air or secondary service air.

A relay is a remote pressure regulator, that copies whatever pressure is put on its input(top/upper front), by manipulating air from a source port(side ports) out to its outlet ports(lower front).

So when you apply park air to release the brakes, it goes in a top port and the anti-comp matches that pressure on its front ports down to the spring chambers. It takes about 60 PSI to develop enough force in the chambers to compress the springs.

When you pull the park handle, that valve vents air out the port in front of the radiator. That drop in pressure is felt at the anticomp input, and it mimics it by dumping air on the outlet lines thru its vent on the bottom of the anticomp valve, trying to match the inlet port pressure.

What are your dash park and emer lights doing when you push in or pull out the park control? Those lights are driven by a 66 PSI switch located under the drivers floor. Is there any delay in tgem changing state when you work the park control.

The only time you should really see a resistance in the park control is when there is no supply air. When the tanks empty, and supply goes away, a stiff spring in the control automatically pops the handle out to the air off/brakes set position...

 

[Lugnuts]

The anticompound is the only component that controls air to the park spring chambers.
It is a relay valve, much like the service brake relay right below it on the crossmember.

It differs from the service relay in that it has a 2way check valve built into its input, so can accept two different inputs, park air or secondary service air.

A relay is a remote pressure regulator, that copies whatever pressure is put on its input(top/upper front), by manipulating air from a source port(side ports) out to its outlet ports(lower front).

So when you apply park air to release the brakes, it goes in a top port and the anti-comp matches that pressure on its front ports down to the spring chambers. It takes about 60 PSI to develop enough force in the chambers to compress the springs.

When you pull the park handle, that valve vents air out the port in front of the radiator. That drop in pressure is felt at the anticomp input, and it mimics it by dumping air on the outlet lines thru its vent on the bottom of the anticomp valve, trying to match the inlet port pressure.

What are your dash park and emer lights doing when you push in or pull out the park control? Those lights are driven by a 66 PSI switch located under the drivers floor. Is there any delay in tgem changing state when you work the park control.

The only time you should really see a resistance in the park control is when there is no supply air. When the tanks empty, and supply goes away, a stiff spring in the control automatically pops the handle out to the air off/brakes set position...

That's a great explanation, thank you.
So when the Parking Brake Control Valve is pulled up to release pressure, if you hear the front quick release air exhaust and the lights on the dash come back on telling that the brakes are applied then if your parking brakes are slow to release it must be the Parking Brake Relay component not exhausting quickly or a mechanical malfunction?
.

 

[Ronmar]

Well its not the front QR you hear, it is the park valve itself venting the air in the line between the park valve and the anti-compound valve. up behind the center of the grill above the center of the radiator is a vent port thru the floor(in under/forward of the heater). That is where the park valve and the pedal/treadle valve(their vents are tied together) vent their air when you release the park or treadle valves.

The park&emer lights coming on as soon as you release the park valve indicate the pressure coming out of the park 2way check-valve under the drivers floor(where the pressure sw is located) has fallen below 66PSI which is pretty close to where the spring park brakes start to engage. The lights coming on immediately(and the woosh heard from out in front) indicate the valve is venting rapidly.

so either there is a restriction/crimp/kink in the park air line between the pressure switch under the drivers floor and the anti-compound, delaying the pressure release at the anti-compound input, or the anti-compound valve is not rapidly matching the pressure drop on the park air line by releasing the air to the park springs rapidly thru its vent.

like I said above, the anti-compound has a 2way check-valve built into its input. park air or secondary service air are applied to it, so it will release the park brake when you step on the pedal so both spring and service pressures cannot compound and possibly damage the brake assembly/wedges. If that little 2way were stuck it might restrict park air changes being felt by the relay portion of the anti-compound valve.

one of my utube vids shows testing the anti-compound function. By leaving the park brake engaged(dash lights lit) putting the transmission in R, bumping the throttle up a little bit then slowly pressing and releasing the brake pedal. If you can see/feel yours lurching a little when transitioning from park brakes to service brakes and back like in the video when you press and release the pedal, then the relay portion of the anti-compound is OK And that built in 2way in the top or the park airline has a restriction. If there is a delay in transitioning from park to service(no lurch/movement), or service back to park(no park, truck starts rolling) when you press and release the pedal, then the relay portion of that valve may be the issue… just remember that if it is an anti-compound relay issue, and the parks delay when being applied during this test, the truck wont transition back to park and will start to roll when you release the pedal, so have room behind you when you do this test. You could also do it going forward, just select mode and arrow down to 1st gear. 1st or R are the lowest gears with the best mechanical advantage to show the lurch the best during the transition…

 

[Lugnuts]

Well its not the front QR you hear, it is the park valve itself venting the air in the line between the park valve and the anti-compound valve. up behind the center of the grill above the center of the radiator is a vent port thru the floor(in under/forward of the heater). That is where the park valve and the pedal/treadle valve(their vents are tied together) vent their air when you release the park or treadle valves.

The park&emer lights coming on as soon as you release the park valve indicate the pressure coming out of the park 2way check-valve under the drivers floor(where the pressure sw is located) has fallen below 66PSI which is pretty close to where the spring park brakes start to engage. The lights coming on immediately(and the woosh heard from out in front) indicate the valve is venting rapidly.

so either there is a restriction/crimp/kink in the park air line between the pressure switch under the drivers floor and the anti-compound, delaying the pressure release at the anti-compound input, or the anti-compound valve is not rapidly matching the pressure drop on the park air line by releasing the air to the park springs rapidly thru its vent.

like I said above, the anti-compound has a 2way check-valve built into its input. park air or secondary service air are applied to it, so it will release the park brake when you step on the pedal so both spring and service pressures cannot compound and possibly damage the brake assembly/wedges. If that little 2way were stuck it might restrict park air changes being felt by the relay portion of the anti-compound valve.

one of my utube vids shows testing the anti-compound function. By leaving the park brake engaged(dash lights lit) putting the transmission in R, bumping the throttle up a little bit then slowly pressing and releasing the brake pedal. If you can see/feel yours lurching a little when transitioning from park brakes to service brakes and back like in the video when you press and release the pedal, then the relay portion of the anti-compound is OK And that built in 2way in the top or the park airline has a restriction. If there is a delay in transitioning from park to service(no lurch/movement), or service back to park(no park, truck starts rolling) when you press and release the pedal, then the relay portion of that valve may be the issue… just remember that if it is an anti-compound relay issue, and the parks delay when being applied during this test, the truck wont transition back to park and will start to roll when you release the pedal, so have room behind you when you do this test. You could also do it going forward, just select mode and arrow down to 1st gear. 1st or R are the lowest gears with the best mechanical advantage to show the lurch the best during the transition…

That's brilliant way to check that, thank you.
As far as the Relay Valve/ Anti-Compound Valve is there a kit that you can pull the whole valve out and rebuild it or is it a valve that if one side fails you replace the whole valve? The truck is 40 miles from me and I would like to minimize my running.
And by the way that test is applicable to all air brakes with Anti-Compound Valves and I think all trucks have that now.
Salute' Sir

 

[Ronmar]

yea the test should be applicable to any truck with an anti-compound configuration. How the brakes are adjusted might effect the results you see, but it is still a matter of the anti-compound rolling off the park as the service is being applied. Like I mentioned in the start of the video, I couldn’t really feel it in 2nd gear/D with the engine at idle. I think the first time I felt it was by accident. I was using the cold wx warm-up procedure, so had it in D with the idle bumped up to get the torque converter making some load and heat. It kind of startled me when I stepped on the brake pedal and felt the lurch as it transitioned between the park and service brake systems… It took a minute before it registered what had happened and I filed it away as a good way to test the anti-compound function…

These valves are getting kind of old, so it might be better to replace it, if it Is the problem. A disassembly and clean might also get it back in service, but I have not seen a rebuild kit for them. The part number in the manual is a N-50024-B. I just saw one on Ebay europe for 84 euros…

Haldex doesn’t list that part currently. I am thinking the comparable current Haldex production part is KN28043, but there are some minor differences. Both valves use 1/2” NPT supply ports, but our original valves use 3/8NPT delivery ports with 90 degree 3/8 to I think -8JIC adapters where the lines to the brake actuators attach. Ours also use 1/4NPT ports for both the control port inputs.

The KN28043 has 1/2” supply ports AND 1/2” NPT delivery ports. It also has one 3/8” and one 1/4” NPT control port. The documentation for it says it comes with bushings and plugs to match OEM applications, and a couple bushings should be all that is necessary to fit it. the configuration and body casting look identical other than the port sizes, and brake relays all basically work the same way(Using supply, they match delivery to whatever pressure is applied to control). A quick search shows that valve from various suppliers $120-180… Haldex does spec a rebuild kit for these valves, whether it is applicable to our original valves, IDK…

 

[Lugnuts]

yea the test should be applicable to any truck with an anti-compound configuration. How the brakes are adjusted might effect the results you see, but it is still a matter of the anti-compound rolling off the park as the service is being applied. Like I mentioned in the start of the video, I couldn’t really feel it in 2nd gear/D with the engine at idle. I think the first time I felt it was by accident. I was using the cold wx warm-up procedure, so had it in D with the idle bumped up to get the torque converter making some load and heat. It kind of startled me when I stepped on the brake pedal and felt the lurch as it transitioned between the park and service brake systems… It took a minute before it registered what had happened and I filed it away as a good way to test the anti-compound function…

These valves are getting kind of old, so it might be better to replace it, if it Is the problem. A disassembly and clean might also get it back in service, but I have not seen a rebuild kit for them. The part number in the manual is a N-50024-B. I just saw one on Ebay europe for 84 euros…

Haldex doesn’t list that part currently. I am thinking the comparable current Haldex production part is KN28043, but there are some minor differences. Both valves use 1/2” NPT supply ports, but our original valves use 3/8NPT delivery ports with 90 degree 3/8 to I think -8JIC adapters where the lines to the brake actuators attach. Ours also use 1/4NPT ports for both the control port inputs.

The KN28043 has 1/2” supply ports AND 1/2” NPT delivery ports. It also has one 3/8” and one 1/4” NPT control port. The documentation for it says it comes with bushings and plugs to match OEM applications, and a couple bushings should be all that is necessary to fit it. the configuration and body casting look identical other than the port sizes, and brake relays all basically work the same way(Using supply, they match delivery to whatever pressure is applied to control). A quick search shows that valve from various suppliers $120-180… Haldex does spec a rebuild kit for these valves, whether it is applicable to our original valves, IDK…

Well Sir, you get the Attaboy for what it is worth. Thank you for sharing the information, the videos, the knowledge, the time. I'll let you know how this turns out and the door has been opened to diagnostic playing. Lugnuts

 

[Lugnuts]

So I wasn't so quick to get back with you how that all turned out. I apologize.
It turned out to be the Relay Valve. When I removed it from its perch it was quite plugged. They you weigh it out and say I could try cleaning it but the cost isn't that terrible versus the inconvenience of location and it had been in there for 20+ years so..... if I would have been in the woods that would have been a different story.
The valve KN28043 was the only valve to put back in there because I found in my search it is the only one with the Anti-Compound built in the valve. And by the way Ronmar Sir, that anti-compound test is phenomenal. Since then I have tested other vehicles and have found out that they really will go bad and you never know it!!! Thanks all for the assistance you have given me in the past and at the present!!!