Spring brake overide

[diverman555]

I am confused here.
I have a M923A1, when I pull out the button on the dash for the spring brake, it sets the brakes and the truck will not move. When I start the truck and after the air builds up to pressure, I push in the button to start driving. When I push in the button the spring brake override light comes on and a very quite buzzing starts coming from the failsafe warning control module.
Question 1. Why does the spring brake override light come on when I push the button in to release the brakes and drive the truck.
Question 2. Why does the buzzer start sounding when I push the button in to release the brakes.

Question 3. Could the spring brake pressure switch in the dash behind the switch be bad, or could the wires be reversed?

Does not seem right that the red light on the dash stay on the entire time I am driving.

Read the TM's and it does not state what the correct way is.
Should the light go off when I push the button in?

 

[91W350]

When the air pressure is up, the truck should roll with the over ride button out. If the pressjre is low, the spring brakes should lock up the tires.

All of ours have a light on when the over ride is shoved in.

 

[Derrickl112]

I think the button has "push to override, pull for normal" printed on it.

 

[jwaller]

you should never push the spring brake override. it's an OVERRIDE. thats why a light comes on, telling you that you are doing something wrong.

leave it out and wait for the air pressure to build up completely and then you can drive it.

Read the -10 on how to operate your truck before you do something really dumb and hurt somebody.

 

[diverman555]

people.

 

[diverman555]

How to answer questions

I wrote in the question that I had read the TM's including -10 but a question can't be asked on here without being the person asking put down. So I will just delete the question.
Glen and Derick thank you for your helpful info.
Another good book is how to win friends and influence people. Explains how to treat people.

 

[WillWagner]

Isn't this covered in a CDL book? You should read that too.

 

[porkysplace]

I wrote in the question that I had read the TM's including -10 but a question can't be asked on here without being the person asking put down. So I will just delete the question.
Glen and Derick thank you for your helpful info.
Another good book is how to win friends and influence people. Explains how to treat people.

So I will just delete the question. This is why you can no longer delete threads , you don't like the answers so you take your toys and go home. I guess this wasn't covered in this book ; How to win friends and influence people.

 

[nf6x]

Neither slamming the OP nor editing out the original question is very good behavior in my opinion. Come on, guys, we can do better than that.

Since I didn't see the original question, I'm going to guess what it might have been about and try to make a constructive response.

I may be mistaken, but I believe that the sole purpose of the spring brake override is to release the spring brakes independently of the mechanical driveline brake so that the operator can adjust the mechanical brake. Otherwise, you wouldn't be able to tell whether the mechanical brake is holding the truck. I think that the override should only be pushed in while adjusting the mechanical brake, and otherwise the parking brakes should only be operated with the parking brake lever. The warning light tells you if the control accidentally got bumped... but only if the master switch is turned on! It is easy to bump the override when working in the cab, and if the truck still has air pressure, then just the driveline brake will be holding the truck. My truck still has enough pressure to make that override do stuff after a week of sitting. Here's another good reason to use wheel chocks, even on a truck with perfectly good brakes.

You can also test the spring brakes independently of the mechanical brake by lowering the parking brake handle and pushing the arm of the valve behind it up. Again, that's just a testing technique, not something to do during regular operation.

Since the military decided to have both a regular air brake system and a backup mechanical driveline brake, all controlled by the mechanical lever rather than traditional air brake controls, then added an override for testing that looks like a traditional air brake control but is not used like one, it's easy to get confused by the M939 series parking brakes at first. They are a bit weird compared to what you would find in other trucks.

 

[quickfarms]

The spring brake over ride is a feature designed to let you move the vehicle off of the road and get it out of the way.

There is only enough air in this system to perform a couple of low speed stops.

It is not found on modern trucks but may still be found on busses.

It is mentioned in the CA CDL hand book

 

[EMD567]

The override is for the time when the enemy is closing in, and you don't have time to build up air pressure. I belive some would call it the "OH CHIT" button, as in LETS GET THE **** OUTTA HERE NOW.

 

[Speddmon]

porky is correct, that is why the delete button was removed. I understand that some people were frustrated by the question, and maybe they phrased their response a bit harshly, but it's time for everybody to grow up a bit. There is no need for the attitudes. I realize that people don't want to have untrained or unknowing people driving large trucks down the road without a complete understanding of them. It's a valid concern. But on the same token, questions are how we all learn. Have enough dignity to admit you don't know everything and take some constructive criticism and move on.

Others, try to remember that you DON'T know everything and you NEVER will!!!! Try to remember that when you answer a question.

I am going to restore the question so others in the future can benefit from it, and this thread will be locked.