Air brake issues - please help!!!

[Entropy455]

I picked up a 1965 Miller 12-ton tilt-bed trailer, and I need help troubleshooting the air brakes.

Here’s a picture of my truck: http://i1192.photobucket.com/albums/aa337/Entropy428/IMG_0898.jpg


Here’s a picture of the trailer: http://i1192.photobucket.com/albums/aa337/Entropy428/IMG_3608_zps762c0e35.jpg


The brakes are air-over-hydraulic. In the following picture you can see: http://i1192.photobucket.com/albums/aa337/Entropy428/IMG_3616_zps62a842e2.jpg, the air-chamber and the master cylinder - but that’s it. There is no air tank, or air control valve on this trailer – both the blue service air hose and the red emergency air hose connect directly to the air-chamber (shown here) http://i1192.photobucket.com/albums/aa337/Entropy428/IMG_3614_zpsee61eea8.jpg


With the gland-hands normally connected to my M923, the trailer brakes lockup hard, and will not release. I did some basic troubleshooting, and here’s what I found. With both air hoses disconnected, the trailer wheels turn freely. When the red emergency hose is pressurized, the trailer brakes engage fully. The blue service hose seems to have no effect when pressurized.


Are my trailer brakes installed correctly? Is my M923 capable of properly controlling this brake setup? Am I doing something wrong?


Please help???

 

[Derrickl112]

Did you try switching the air lines?

 

[Entropy455]

I just went out and took another look at the air-chamber (shown here) http://i1192.photobucket.com/albums/...psee61eea8.jpg It appears that the red hose is threaded into the service port, and the blue hose is threaded into the emergency port. They are are crossed! Judging by the dirt, they've been crossed for a while.

Could it be this easy? If I swap the hoses, will the brakes function as designed?

I'm assuming that I'll need to adjust spring-preload on the air-chamber's threaded rod, to adjust the breaking intensity so that the trailer is dialed in with my 5-ton's air system???

 

[quickfarms]

I have never seen a system like this. Usually the red, emergency, line pressurizes the system and releases the spring brakes. The blue, service, line sends a small amount of air to the relay valve that opens up to let air flow from the tank or emergency line into the brakes.

That threaded rod in the air can appears to be a caging bolt used to manually release the spring brakes

 

[doghead]

The air chamber in the picture is caged.

We prefer you to attach photos, rather than link them.

 

[hemichallenger]

Can you post a picture of the brake assembly. Most air over hydraulic will have a shoe adjustment. I could not access your photos. Did the brakes work with the lines swapped. They should work on your 923. Some old systems do not have tanks and relay valves.

 

[Entropy455]

Ok, files are directly attached. The trailer brakes are not spring brakes. They are air-over- hydraulic. The trailer has no air tank, air valve, or any other air components - just the air-chamber shown (picture from above, and below). The air chamber is connected directly to a hydraulic master cylinder via mechanical shaft. From there, it is a standard hydraulic drum brake setup all the way - with traditional hydraulic brake lines.

Is it just me, or does this seem like a hillbilly setup???

 

[Derrickl112]

I can not speak for the rest of your trailer's brake system, but that is definitely an air springbrake chamber shown in your pictures.

http://www.google.com/search?safe=o...rce=og&sa=N&tab=wi&ei=_m2ZUfrSGsXe4APHzYCQDg#

There is a spring inside the chamber to engage the brakes when there is no air pressure in the lines. The bolt on the end is used to unlock the brakes so the trailer can move without having to connect the air lines. How is that chamber used on your trailer? I have no idea....

 

[Entropy455]

Here's another round of pictures. The master cylinder is more clear. You can also see where the service hose is connected to the emergency port on the air-chamber.

I'm trying to figure out how this system "should" work. It appears to be a differential system. Where the emergency air is always under pressure, trying to actuate the master cylinder. The service air is normally under pressure, preventing the hydraulic cylinder from actuating. When the M923 brakes engage, the service line pressure drops, and the emergency air overtakes the mechanism, and engages the trailer brakes.

If the trailer ever breaks loose from the truck, there's no brakes. I believe this was legal in the 1960s when this trailer was built. . . .


Am I close????

 

[hemichallenger]

The spring brake can is caged so you have no parking brake. The service line should go to the line that leads to closest fitting inlet on your can that connects to the brakes. It should work with only the service line hooked up. If you want the spring brakes to work apply air to the red side. That should be the one colsest to the end of the can by the caging bolt. Then take a 3/4 wrench and loosen the bolt and turn it a 1/2 turn and it should come out. You do not need a air tank or any valves to make this system work.

 

[doghead]

It appears that that is a dual chamber 30/30 brake chamber. And perhaps they are simply only using the service brake side. That would explain the cage bolt.

Did you try crossing the lines?


In the last picture, the rim clamps look like angle iron. Are they correct parts?

 

[hemichallenger]

This is a commen system where emergency air is always on to release the brakes. When you apply service air it applys the brakes. The emergency air releases the spring brake that is your parking brake. You are right is is now not legel to not have a brake that does not come on if the trailer should disconect.

 

[tobyS]

If you google air over hydraulic brakes, I think you will see two systems, of which you have the kind with no break away brakes. You may need to have a tank and valve for making it modern.

 

[Entropy455]

I'm a little confused. Please forgive my lack on knowledge on is subject, but what does it mean when you say that the spring brake is caged?

Note that my trailer rolls freely when completely disconnected from air. There is no default spring engagement of the brakes when air is lost. The air chamber must only depress the hydraulic cylinder to actuate the brakes. There's no other mechanical connection to the drums, other than the hydraulic lines. In troubleshooting, I hooked up my shop air compressor to the red hose, and it directly actuates the master cylinder (engages the brakes). When I hook up air pressure to the blue hose, nothing happens whatsoever.

This system seems counterintuitive to me. When I connected the red hose with the red connection on my M923, and the blue with the blue connection, the trailer brakes locked up completely - regardless of whether or not I was pressing the M923's brake.

It was my understanding that the red connection on my truck is always under full system pressure. And the blue connection is modulated - in that it's under high pressure while driving, and the pressure is metered down proportionally when hitting the brakes. If this is correct, then what I can't figure out is how in the world this could work with my darn trailer?

 

[Derrickl112]

The spring does not engage because the bolt on the back of the chamber is holding it back. Removing that bolt should engage the brakes without the use of air.

 

[Entropy455]

I have not attempted to cross the lines yet. The truck is already put away for the evening. I will attempt it tomorrow.


It seems crazy to me that the prior owner would hook the red to blue, and blue to red - for decades of trailer use - in lieu of simply swapping hoses for proper color coding.


Do I need to retrofit this trailer with breakaway brakes? Or am I grandfathered into the law with the old style brakes?


Also - the blue connection on my M923 - is this line normally pressurized, where air pressure drops to engage the brakes? Or do I have it backwards - where the pressure is normally low, and increases to engage the brakes???

As of now, the brakes do not work when connected to my M923. . . .

 

[hemichallenger]

The bolt in the middle of your brake can is a caging bolt. There is a diaphram, plate and a spring in the back half of the can. The cagging bolt goes into the plate and when it is tightened it makes the spring compress so you have no spring or parking brake. Your air lines are reversed somewere and that is why when you put air to the red the brakes come on. You have no parking brake because the spring is caged with the bolt that you need to remove with the 3/4 wrench. You do not need any tanks or valves to make this system work. It would respond faster if you added a tank and relay valve but it is not nessary. This is a very simple system. The good news is your brakes are working and I would switch the lines and take the cagging bolt out. They may have had to move it with a truck that was not air brake or you may find that the can leaks and that is why it was cagged.

 

[Derrickl112]

This might help...
Skip to 5:30
http://www.youtube.com/watch?v=3mrUMTP4thI

 

[hemichallenger]

This might help...
Skip to 5:30
http://www.youtube.com/watch?v=3mrUMTP4thI

Thats a air brake system

 

[Derrickl112]

Thats a air brake system

Correct, but, his trailer uses an air spring brake chamber and he has no idea how the chamber operates.