M135 Brake question....

[Brad]

Sometimes when pushing the brake peddle it seems like it is hitting something solid and will go no farther?
Usually the brakes are fine and work perfectly, but about a quarter of the time the peddle will start down and then it's just like the linkage was hitting something solid.
But it is not. Everythiing is clear.
I am not familiar with how these air / hydraulic brakes operate. Anyone know what might be goung on???
Thanks,
Brad

 

[YkDave]

the brakes are full hydraulic w/ air assist. they are pretty easy to troubleshoot.

Its hard to say what it is without being there, but my guess would be either a master cylinder issue (which their is a possibility of the piston jamming up), then their is also the possibility of an air pack (air assist) issue which would make the pedal extremely stiff

 

[rosco]

If the brakes are in need of adjustment, the pedal will go all the way, or close to all the way to the floor. Successive pedal strokes will get shorter and shorter/firmer and firmer, until the pedal travels very little, and is very solid!

Don't try to trouble shoot the system, unless it has first been properly adjusted. If you can't make the proper adjustments, then it needs repair! Sounds like the brakes need adjustment. Many of these vehicles continue to operate, in spite of excessive "deferred maintenance".

 

[rosco]

BTW, When adjusting these brakes, I find it beneficial to jack up both ends of the same axle, that will let you rotate each wheel end, during adjustment.

Lee

 

[hippiedude]

There is one more place to look if you feel it is the brackpedal is bindig up ..... here on page 464 of tm-9-8024 figure 240.....E,G,H,J,K ........That joint on my truck was rusted solid .....Had to remove the pedal assembaly ( half to three quarters of houre ) Heat up to free it up ..... two hours max ....... like new now ......... Check it out .... If you can move it by hand your ok ...... if not try there first .......... Tim

 

[hippiedude]

ops no pic .............

 

[hippiedude]

Sorry pic don`t work ........E- brake pedal lower half , G- pullback spring , H-yoke , K-piston pushrod .......... Hope that helps ......... Tim

 

[Mastertech]

actually It sounds like what YKDave said. Its more than likely a problem inside the airPack I had a simular problem After I finished up with the complete Brake system rebuild Including repalcing all Brake hard lines. I bleed the system with a power bleeder at every bleeder on the truck until I had absolutly clear clean fluid with no air, and the brakes worked great except like you said some times you would get a little kick in the pedal and then it would get hard. I still had good brakes just no power assist. so I went thru and just hit each bleeder again with the power bleeder on the system, never got any air out that I could see but after that the brakes work exccellent everytime now. So I contribute it to an air bubble getting caught in control valve inside the AirPack. But ya you might just try bleeding it more.

Byron

 

[YkDave]

yes, god only knows the crap that could be floating around in the brake system on these things, and it doesnt take much to start f'n with the small valves in the system (the old dodge truck RWABS were real bad for this!)

Sometimes pushing a jug of brake fluid through the system is enough to clean it out or at least move the contamination to another less problematic part of the system!

 

[hippiedude]

 

[nattieleather]

Adjust the brakes on the wheels. I found this helped the peddle out a lot. It's so easy to do too. I love adjusting the brakes on my old M211 vrs on my old M35.