Air/hydraulic brakes

[JAYHAWK 1962]

OK I am sure this has been asked before but.... i know semi trucks/trailers with air brakes have to have air supplied at all times or they for safety reasons go into a braked position and will not move. how about the m35a2 trucks. if we are towing one that does not run, is there something the brakes have to have done to them so the truck will roll ??? thanks in advance
ALSO where would you run air line to truck being towed ? do the gladhands hook from rear of towing truck to rear of towed truck, or somewhere else?? thanks again

 

[jeep-Jeep]

bleed out the air .
military unlike civilian is designed to get out of a war zone rather than dead end for safety reasons upon failure

 

[dittle]

Just take off the hand brake. The idea of the brake system on a deuce is not that much than different a regular car. Difference is on a car you have a vacuum assist (call it vacuum over hydraulics if you like) where on a deuce you have an air assist (air over hydraulics if you like). You will have a little bit of braking ability (if there is nothing else wrong with the brake system) but not nearly as much as with air pressure behind it. Same thing with your car....turn the car off and then see how much stopping force you have versus when there is vacuum helping it.

 

[papabear]

No is the short answer. The brakes do not "lock down" without air.

The air assist for the brakes is just that...assist. You can stop with the air buzzer going crazy and zero air pressure...but it's a scary experience and takes a long time!!!

If you are towing a disabled truck...you should connect the airlines so the brakes of the towed vehicle can be used.

Also...don't try to tow anything bigger than the tow vehicle...even with brakes

 

[dittle]

Well said PB, just got back from towing my neighbor's deuce with my deuce down to where he was going to store it. On the way down on the interstate his deuce started blowing diesel out up by the IP. He didn't look at it along the interstate but its in a safe enviroment now to look at it.

Note on towing.......when turning onto gravel roads from paved roads even at very low speeds you might end up having your heart rate speed up. When we turned today it was on a downhill slope that went to the side as well. I learned how to power slide my deuce at 4mph on gravel....not something that I want to repeat.

 

[Keith_J]

For one more detail on why the M35 has air assisted brakes, look at the brake shoes. They are the same, front and rear. This reduces parts count but also means there is no "servo effect" as is common with all passenger car drum brakes made in the past 50 years. In a servo drum brake, the torque from stopping causes the brake shoes to "cam out", making their contact force greater than that supplied by the hydraulic pressure.

Not so in the M35. Power assist from air pressure is needed. Remember, braking force is proportional to the force causing the friction material to contact the drum.

 

[poppop]

When towing a Duece you can't just hook up the gladhands and have brakes. You have to attach an air line to the airpac. I made a fitting for mine that goes in where the air is supplied when you apply brakes. Only takes a couple minutes to remove one line and install the fitting. There are two types of air pacs and one is easier to do than the other. On a five ton you just attach the gladhands and go. If towing with a tractor truck then the hand valve will apply only the brakes on the towed vehicle if needed.