The Stovebolt Site Forums The Parking Lot Big Bolts Air brake woes: single axle 860 w/ 6-71

Happy spring everyone!
Mine is happy except I'm less happy when I'm dealing with my 860's rear spring air brake troubles. Front brakes work fine. The control and delivery lines lead (1) from the in-cab treadle valve(new) and (2) the frame mounted air reservoir to a "relay" valve at the rear axle then connecting via hoses to the pot on each brake. The original valve at the rear was leaking so I installed what I thought would work: a Haldex 103081X modulating emergency relief valve. The problem is my rear brakes will not release whatsoever. This Haldex valve has what looks to be an adjusting screw which I varied to no avail. If I cut air supply to my rear axle I'm good to go but bad to stop. Do I have the wrong valve here or what the heck am I doing wrong? Thoughts anyone? Thank you. Charley.

Not sure what the valve is you put on. Was it a replacement for the relay valve?

Dear Hevyhauler,

Haldex refers to this valve as an "emergency/relay valve". It is, in my words, an air handler ie: one high volume line in, two hi volume lines out. Also has a signal line in. Acts as an emergency valve for low air situations. At this juncture I know little more then this. Thank you for inquiring. Charley.

That valve should be adequate to release the spring brakes, but it will not work with the service brake section of the spring brake pot. The two output lines should be plumbed to the "Park" lines of the spring brake chambers, with direct system pressure plumbed to the input line of the valve. The pilot valve line needs to be plumbed to the in-cab parking brake release valve. Air pressure from the pilot line opens the relay valve and sends full air pressure to the spring brake release. If pressure drops at the relay port, due to pulling the park valve out or loss of system pressure, the spring brakes apply.

You'll need another valve from the foot pedal to modulate pressure to the service brakes for stopping. That system uses a different type of relay valve, not a simple on/off type.
Jerry

Hy stoveboltcharley, If your truck is equipped with spring brakes then you need a valve to control their operation, and a valve or quick release to control your regular service brakes. If you had a functioning spring brake system with a leaking valve why would you replace that valve with a valve that did not match the original valve? Can you tell us the name and or part number of the valve you removed?

Here is a rather simple schematic of a BW air brake system.

https://plus.google.com/10819770718...5163251346&oid=108197707187186692269

The illustration shows a MV3 Valve which was not available until about the 80's. Older trucks used a toggle type valve for the trailer and a push pull button for the spring brakes.


I would not recommend using Haldex because if you don't have the particular number you need, you will probably get the wrong thing. Haldex is aftermarket and most parts people are clueless as to what is what is what. Tractors have used a BW R12 or R14 valve for over 50 years. I order mine from Peterbilt in Minneapolis.
https://www.peterbiltparts.com/brak...0483bxw?gclid=CIPyxcmo8sQCFQwtaQodcTIAJw

The illustration is actually upside down. For the quick release for the spring brakes, all you need in back is a simple quick release valve.

http://www.finditparts.com/products...564&gclid=CJWTpMKp8sQCFQioaQodY0IAdg

Peterbilt is probably cheaper, but their server is very slow tonight.

On the dash the generic name for the valve is PP1. Here I think a Haldex can probably be bought cheaper. http://www.ryderfleetproducts.com/r...uct&gclid=CPP3652t8sQCFdYkgQodjKEAdw

Your truck may very well not have come from the factory with spring brakes. MGM invented them in 1956 or so and they were an option for quite a few years. My 1962 International DCOF 405 came from the factory with MGM spring brakes, but by then International had gotten way ahead of GMC in heavy trucks. Your spring brakes may well have been added later on by someone who didn't really understand what they were doing.

04/18/15 @ 2200.
Thought to come back and check if any mail. There is some and this is good. My sincere thank you to the folks who have responded. With your input I believe that I may be able to pander to my old trucks peculiarities. We shall see. Here is a general question to the masses: What component is the most elusive when endevouring to restore any old truck? Answer: Perseverance. I gotta keep telling myself this. Charley.

There is no part number identifying which valve is it that failed me. I had to take a shot at it. My woes. Thank you just the same for inquiring. Charley.

Hy stoveboltcharley, could you post a picture of the valve which failed, there are a lot of experienced eyes here that could probably identify the valve for you.

Dear Shop Shark,
I would be tickled to post a pic of the old valve, thank you. Possibly someone will find this valve as familiar. Will hold it back when I sell off the contents of the scrap box to the J-Y. Thanks again. Charley.

I just went back and looked at your first post. If you installed a Haldex 103081X modulating valve, you probably don't have the system to support it. The purpose of this particular valve is to divert air from the service chambers and apply the spring brakes if the service brakes fail. I'm sure you don't have a system that sophisticated on a 50 something year old truck. All you need is an R12 relay valve and a quick release for your spring brakes. How did you wind up with a Haldex modulating valve anyway?

If you have a valve with a port on top and a port on each side and an exhaust at the bottom mounted on the back cross member, it is probably a quick release valve.

http://www.finditparts.com/products...564&gclid=CJWTpMKp8sQCFQioaQodY0IAdg

They come in plastic or pot metal. Trying to match them up by looks can be deceiving. Manufacturers are always changing the looks of the valves. You need to by them by what they need to do.

If you have a valve with a small line going to the treadle valve, a big line going to an air tank and a line to the air chambers at the port closest to the slack adjuster that is leaking, you need an R12 Valve. They come in all shapes and sizes, but the function is the same. On this particular one, the small port on top would go to your treadle valve, the larger port on the side to an air tank and two on the bottom to your chambers and two would be plugged.

http://www.amazon.com/Bendix-Style-Vertical-Delivery-102626/dp/B005458HWE

Most of them come with 4 service ports for a tandem rear. With a single axle, you simply plug two of the ports.