M 35 trailer brake

andyindy

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Rising Sun Indiana
I have put a "jockey handle" from a M275 tractor on my M 35 to control brakes on 20 ton drag. I have the air supply to the valve from under the dash hooked up and believe this is correct, as used original plumbing from donor. I traced the service line from the rear of truck up to air pac. It looked as tho the service line and the T for the brake light switch are tied together. I extended the brake switch forward and added a T fitting to accept the outlet side of trailer valve.Hooked up like this will supply air to service brake outlet, and regular brakes also work correctly, supplying air to service brake trailer connection.
However, when the trailer valve is pulled, with no trailer connected you can hear air flowing to front of truck. I've studied my TM ( THANKS DOC!) air diagram of tractor and see a double check valve installed. Hard to tell where it is actually at on truck. Also see a shuttle valve in diagram. What is purpose of shuttle valve? I think I'm close, but need some help to finish up, not really sure what to do next.Any one have any ideas? THANKS, Andy......
 

gimpyrobb

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Sure wish I could help on this Andy but I have no clue. I'm sure someone that knows will be along soon.
 

m-35tom

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when the brakes are not applied, the service line is vented to the line that goes up the firewall near the air filter. so if you put air into the service line, it will just go out the vent. when you apply the brakes this vent is closed by a valve in the airpack and this vent line cannot be blocked or brakes will not release. i am not sure you can do what you want on m-35 brakes without much more replumbing. sounds like you want manual control of the rear service gladhand. to do so you will have to seperate the rear service line from the airpack and have it go to the hand valve only.
 

gimpyrobb

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Tom, why would the line have to come from the airpack? If he wants to work the trailer brakes seperate from the truck brakes, wouldn't any air line plumbed to the "johnny bar" work, as long as there is a check valve in the system so it doesn't back feed the truck?
 

tm america

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yes you could run the line straight to the gladhand as long as you put a check valve b to prevent it from back feeding to the airpack and you will also need someway of venting the air from the line after the handle is released so the trailer brakes dont stay applied when the trailer valve is released
 

Recovry4x4

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The trolley brake handle should vent in the cab. There are 3 steel lines running to it.
 

andyindy

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Thanks guys, some more ideas to think about. Does any one know the how and why of the shuttle valve on the tractors? I think it is located at the bottom of the pogo stick. I've managed to glean this from the TM. Thanks Andy............
 
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