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air assist working?

porkysplace

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How can I tell if the brake air assist is working? Don't want to replace it if I don't have to.
A little better description of your problem is needed .
Do the brakes work?
Do you push yourself off the seat trying to push the brakes ?
Do the brakes stay on when you push the brake pedal ?
 

exoilfld

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Just got the truck. The mc was dry. Added fluid, but no brakes either with or without air. Have not bled at the wheels yet. Pedal goes to floor with very little resistance.
 

porkysplace

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Just got the truck. The mc was dry. Added fluid, but no brakes either with or without air. Have not bled at the wheels yet. Pedal goes to floor with very little resistance.
You have to bleed the system to even start to try and get them working , bleed the air-pac first then the farthest wheel and work toward the closest wheel last.
 

exoilfld

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I planned on that, but seems there should be some pedal since there is fluid at the wheels. The fluid I bought is dot5 and is a purple color. The fluid at the wheels is just clear so far. I can't beleve how expensive the dot 5 fluid is.
 

porkysplace

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I planned on that, but seems there should be some pedal since there is fluid at the wheels. The fluid I bought is dot5 and is a purple color. The fluid at the wheels is just clear so far. I can't beleve how expensive the dot 5 fluid is.
Until you get the air out of the lines you won't have any pressure on the pedal and if the MC was empty the air is between the old fluid and the new fluid . Figure on a gallon of brake fluid before you get it bled out. Did you build a power bleeder ?
[h=1]Deuce Power Bleeder R4x4 Style[/h]
 

dmetalmiki

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Still wonder how you know if the air assist is working.
What vehicle is this?
But generally, If you have an M series old truck, then, If it is not working you will not stop it.
If it is working, you will be able to stop it, IF the brakes are serviced bled adjusted and functioning properly.
 

porkysplace

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Still wonder how you know if the air assist is working.
The brakes need to be working to tell . Usually when they go bad you either have a hard petal ( no assist ) or they keep applying pressure and the brakes drag or lock . If it is a questionable truck you may be better off pulling all the drums and inspect the wheel cylinders and brake lining as well as wheel bearings . If you don't know the service history and it hasn't been serviced recently this is a must do or you could be pouring a lot of DOT 5 on the ground and still have unsafe brakes.


This will be of some help.
TB-9-2300-426-20.pdf TB-9-2300-426-20 Hydraulic and Air Hydraulic Brakes preventive maintenance.


TB43-0002-87.pdf TB43-0002-87 Brake fluid replacement procedure.


http://www.jatonkam35s.com/DeuceTechnicalManuals/Tm9-1827cBrakesWagnerLockheed1944.pdf
 
Last edited:

sandcobra164

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Piggybacking off what Porkysplace posted, you would do yourself a favor to inspect / service the entire braking system on the truck prior to doing much else with it. This includes removing all the wheels, hub/brake drum assemblies and inspect/adjust/replace any questionable components. A dry Master Cylinder means the brake fluid had to have gone somewhere it shouldn't have gone. Common leaks are at the wheel cylinders and master cylinder, other possible leaks are a bypassing airpack (booster below the master cylinder), rubber hoses and maybe the steel lines. Most M35's have a single circuit braking system which means one failure point resulting in a leak can easily result in no brakes at all. The emergency brake does very little to slow the truck in a panic situation. A small quantity of Air Force Deuces manufactured in the late 1980's had a dual circuit system but ALL brakes need to be operational on a 13,000 pound truck in either case.

Now to briefly answer your original question. Start the truck, let it build air to around 120 psi. Shut the truck off, press and release the brake pedal. If the "air assist" is working, you'll hear a burst of air releasing when you let off of the brake pedal. You normally don't hear it if the truck is running on the Deuces. On the M809 and M39 series 5 tons you can hear the airpack release air with the truck running.
 
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