m1083

[Zeke]

Brake issues. The brakes work great. Just the parking brake is not working. I can pull the valve in the cab and hear air inside the cab as you should. But I don't hear the large release outside the truck. With the parking break applied the truck still rolls. Ideas? Im trying the valve first, looking for the right part numbers to order one.

 

[simp5782]

Are the brakes caged?

 

[Zeke]

Are the brakes caged?

Please elaborate. These are air brakes, wedge style. foot break works great. No parking break working when we pull the knob on the dash.

 

[simp5782]

Please elaborate. These are air brakes, wedge style. foot break works great. No parking break working when we pull the knob on the dash.

If you don't know what caging the brakes means then you shouldn't be touching the air brake system.

Please take it to a shop

 

[Zeke]

If you don't know what caging the brakes means then you shouldn't be touching the air brake system.

Please take it to a shop

Thank you for your concern. However I am just supporting the mechanics from the site. They are having issues with the truck. I am looking for conundrums on my own to try to help diagnose the issue. If I were as experienced as you, I wouldn't need to reference help from the site it seems. God Forbid anyone try to educate themselves from a great resource such as this. Maybe I don't have the security clearance to inquire. As I said in the thread. The brakes work fine from the pedal. If they were caged, the brakes would not work. I am familiar with the function, the terminology slips my mind as I am not a mechanic.

 

[WillWagner]

NO, Simp is trying to tell you that if you do not have the knowledge on how the system works, it is not safe to you or others around you to try and educate yourself and then experiment with things that can kill you or others. It is a good thing to learn how things work, we all start out that way, learning. Tearing into a rear end, trans, engine, electrical systems and putting it all back together are one thing, but brakes, even non air systems, unless you are well versed and have a working knowledge of how the system works, aren't something you should try and tackle alone/without some sort of experienced supervision.

I am moving this to the correct forum. Hopefully someone will see this and you can get together and you can get to know your truck, repair it and safely drive/have fun with it.

This hobby is under a microscope. When something happens, like an accident, the politicians have a field day and want to ban these vehicles from on road use, look what has been happening with HMMWVs and even you type of truck in other states.

 

[simp5782]

Thank you for your concern. However I am just supporting the mechanics from the site. They are having issues with the truck. I am looking for conundrums on my own to try to help diagnose the issue. If I were as experienced as you, I wouldn't need to reference help from the site it seems. God Forbid anyone try to educate themselves from a great resource such as this. Maybe I don't have the security clearance to inquire. As I said in the thread. The brakes work fine from the pedal. If they were caged, the brakes would not work. I am familiar with the function, the terminology slips my mind as I am not a mechanic.

Wedge brakes will still work even caged. The caging only release the springs brakes that are for parking. The inner service brakes still work as designed.

 

[m715mike]

Wedge brakes will still work even caged. The caging only release the springs brakes that are for parking. The inner service brakes still work as designed.

Wes, if I understand correctly, this is a difference between a 939 series 5 Ton and a commercial OTR truck, right?

 

[Zeke]

NO, Simp is trying to tell you that if you do not have the knowledge on how the system works, it is not safe to you or others around you to try and educate yourself and then experiment with things that can kill you or others. It is a good thing to learn how things work, we all start out that way, learning. Tearing into a rear end, trans, engine, electrical systems and putting it all back together are one thing, but brakes, even non air systems, unless you are well versed and have a working knowledge of how the system works, aren't something you should try and tackle alone/without some sort of experienced supervision.

I am moving this to the correct forum. Hopefully someone will see this and you can get together and you can get to know your truck, repair it and safely drive/have fun with it.

This hobby is under a microscope. When something happens, like an accident, the politicians have a field day and want to ban these vehicles from on road use, look what has been happening with HMMWVs and even you type of truck in other states.

I completely understand, I do know how things work. This is a case of semantics. The term, was not what I knew it as. I have been driving trucks for 30 years. I have performed this "caging" many times. The confusing part for me is mostly, I said the brakes work. The parking brake does not. Caging is not something we would miss at this point. They are not "Caged"........ So before we all dive into this truck, that is a bit different from my experience and my crews recent experiences, I am here asking advice. Now, my crew, both have 70 years combined experience as mechanics and one is a veteran military mechanic. There is no concern here. Just looking for advice as to what we can look for with the symptoms we have. Is it not strange to have working brakes but no emergency brake? Same system, same brakes do the work. Is it as simple as changing the dash valve or is there something extra with the M-1083 that you all might know that I do not. I personally looked under the truck, the chambers all have their plugs in the appropriate places. The Caging jack screws are NOT in place.

 

[simp5782]

Wes, if I understand correctly, this is a difference between a 939 series 5 Ton and a commercial OTR truck, right?

Commercial trucks use S cam and some air disc brakes nowadays.

Wedge brakes is 70s technology. Military just stuck with it with its dual redundancies

 

[Zeke]

I completely understand, I do know how things work. This is a case of semantics. The term, was not what I knew it as. I have been driving trucks for 30 years. I have performed this "caging" many times. The confusing part for me is mostly, I said the brakes work. The parking brake does not. Caging is not something we would miss at this point. They are not "Caged"........ So before we all dive into this truck, that is a bit different from my experience and my crews recent experiences, I am here asking advice. Now, my crew, both have 70 years combined experience as mechanics and one is a veteran military mechanic. There is no concern here. Just looking for advice as to what we can look for with the symptoms we have. Is it not strange to have working brakes but no emergency brake? Same system, same brakes do the work. Is it as simple as changing the dash valve or is there something extra with the M-1083 that you all might know that I do not.

Commercial trucks use S cam and some air disc brakes nowadays.

Wedge brakes is 70s technology. Military just stuck with it with its dual redundancies

 

[simp5782]

Spring brakes are used for parking. Service brakes are used for stopping. Once again the brakes will operate fine with the springs caged. Your remark lead me to think you didn't know what caging is. 70 years of commercial repair experience means nothing on most of the military trucks. Including FMTVs and M939 series trucks. They have more air lines and backup redundancies than any commercial truck thinks to have. It can be challenging tracking things down.

Do the parking brakes set with no air in the tanks?

Remove all glandhands and make sure they are not obstructed.

Use shop air to charge the air tanks. Chock the wheels.Remove the dash valve. Remove a delivery port and see if it is blowing by the flapper with the parking brake disengaged.

If yes. Replace the unit.
If no. There is a check valve behind the front bumper the emergency side air line goes to and releases the brakes automatically for towing. This sometimes gets crossed and gets air from the tanks

Check that and report back.

 

[simp5782]

Wes, if I understand correctly, this is a difference between a 939 series 5 Ton and a commercial OTR truck, right?

Big difference. 939s have spring brake overrides and linear valves that serve the same purpose but have other functions as well as making sure the driveline brake it set for safety as well as locking spring brakes.

On a 939 most folks will go cross-eyed and mentally retarded from the amount of air lines and what goes to which and where.

 

[Ronmar]

Quick check, open all the tank drains and drain all the air. Is the park brake set now as no air = spring park brake application.

Are the front glad-hands vented. If not, air from a leaking 2way or supply check-valve will be trapped in the red emer line and be applied to the park brake system the same as a towing vehicle would to release the park brakes on the towed vehicle...

Air trapped behind a capped front blue service glad-hand will cause the service brakes not to release after you step on the pedal.

The rear glad-hands must be capped...

 

[SausageGuy]

I had a problem with my service brakes working but parking brake would not engage till airtank was drained. Found a 12 inch line by rear trailer protection valve that was kinked and trapping air. Moved it and air vented and truck stopped rolling. Replaced line with a longer one routed in circular route.

 

[Zeke]

Spring brakes are used for parking. Service brakes are used for stopping. Once again the brakes will operate fine with the springs caged. Your remark lead me to think you didn't know what caging is. 70 years of commercial repair experience means nothing on most of the military trucks. Including FMTVs and M939 series trucks. They have more air lines and backup redundancies than any commercial truck thinks to have. It can be challenging tracking things down.

Do the parking brakes set with no air in the tanks?

Remove all glandhands and make sure they are not obstructed.

Use shop air to charge the air tanks. Chock the wheels.Remove the dash valve. Remove a delivery port and see if it is blowing by the flapper with the parking brake disengaged.

If yes. Replace the unit.
If no. There is a check valve behind the front bumper the emergency side air line goes to and releases the brakes automatically for towing. This sometimes gets crossed and gets air from the tanks

Check that and report back.

Printed and given to the mechanics. Thank You. We will certainly report back.