Spring Brake Emergency Control

[rneely]

I can find what it is in the TM but don't see a clear explanation of how and when to use it. On my M925 I haven't had any problems and it has always been in the pushed position, bur reading it again today it seems like it should be pulled as the knob says "Pull for Normal". A simple explanation would be helpful

 

[73m819]

There is a separate air supply this controls to RELEASE the spring brakes in case of a emg. (dead engine, ect.), it is in the closed position (out) for normal operation, open (in) when the truck needs to be moved but the engine will not start.

 

[armytruck63]

Somebody needs to RTFM.

Start here: http://www.steelsoldiers.com/upload/939/TM9-2320-272-10.pdf

 

[Rmtaunton]

Easy , we all have a question at times .

 

[Rmtaunton]

And armytruck and 73m818 both give great explanations

 

[quickfarms]

It is also covered in the CDL manual. This is common on buses so you can get the bus off the road for safety. There is enough air in this system for a couple of applications of the brakes.

 

[wreckerman893]

The other day I was moving the M936 around the yard. I took off the emergency brake but the brakes remained locked. I pushed in the button and pulled it back out and the brakes released. Go figure.

 

[hklvette]

I use the override when toggling the parking brake a lot, such as when I'm pulling out trees. Keeps the spring brakes from dumping their air, decreasing load on the air system.

 

[rneely]

I've read the TM and the paragraph on the control knob says "SPRING BRAKE RELEASE CONTROL VALVE – Pushed in to release
spring brakes independently of mechanical parking brake. Control is also used to
release spring brakes in order to test and adjust mechanical brake". So, 73m819, by your explanation I should be driving with it pulled out and only push it in when I have an air loss that affects the brakes?? Still confusing but air normally pushes spring, loss of air requires caging which is a bolt that pushes the spring, right?

 

[quickfarms]

There is more than just the TM.

Read my previous post

 

[wheelspinner]

The piece missing from the understanding is that emergency air systems such as these are equipped with their own air tank, Item (AA) on the foldout air charts. This is an EMERGENCY supply of air, independent from all other air supplies or tanks. In the event of a catastrophic air loss in the system, releasing this air allows release of the spring brakes to move away from the danger (battlefield exposure, rail road crossing, etc). In operation of the vehicle that is the ONLY reason for ever pushing in that button. If you don't understand why and when spring brakes are activated, you will never understand this particular feature.

 

[quickfarms]

The problem is the OP does not understand all of the functions of the air brake system.

The idea behind this valve, and sub system being added to the air brakes, that is not typically found on commercial trucks is to give the driver a way to hopefully get out of the kill box and to relative safety o. The battle field.

The good new is that there are multiple safety features built into the system.

 

[goldneagle]

I've read the TM and the paragraph on the control knob says "SPRING BRAKE RELEASE CONTROL VALVE – Pushed in to release
spring brakes independently of mechanical parking brake. Control is also used to
release spring brakes in order to test and adjust mechanical brake". So, 73m819, by your explanation I should be driving with it pulled out and only push it in when I have an air loss that affects the brakes?? Still confusing but air normally pushes spring, loss of air requires caging which is a bolt that pushes the spring, right?

WRONG! It's the opposite. Spring brakes are engaged if no air present. It's a safety thing. Air is fed to a diaphragm that pulls the springs back and lets the brake release. When caging the brakes you are pulling the springs back and releasing the brakes.
Basicly I think the air brake system is superior to hydraulic. In hydraulic system if you have catastrophic failure you have no brakes. In an air system the brakes would lock up (engage) and keep the truck from moving. I feel much safer in a M939 than a M818 or M35 truck.