ABS Brakes on a Bobbed M939 series truck

[KaiserM109]

I am considering bobbing my M923A1, so I crawled under it to see what I was going to have to unhook, remove, etc and I spotted the ABS sensor. I am afraid that I can’t just unhook it because the ABS controller will probably think the wheel is locked up and start pulsing the brakes.

I have seen several threads on bobbing a 5 ton, and I believe that all M939 series have probably been upgraded to ABS brakes because of the issue with killing the engine and losing power steering when the driver locks the brakes. Therefore someone out there in SS land must have addressed this problem already. I would like to hear what you think about it, what you know and what you think you know.

Arlyn

 

[M35A2-AZ]

On the ABS, unhook the wires from the unit and pull the 15amp fuse from under the dash on the driver side and you will be fine.

 

[73m819]

Why can't you just use the rear axle that has the rotation sensors, just do away with the middle axle.

 

[KaiserM109]

On the ABS, unhook the wires from the unit and pull the 15amp fuse from under the dash on the driver side and you will be fine.

Bad idea; that disables the ABS completely and M939 series trucks without ABS have a history stalling the engine when the driver locks up the brakes. Then … there is no power steering.

Why can't you just use the rear axle that has the rotation sensors, just do away with the middle axle.

Great idea, thanks. I was assuming that all 6 wheels had ABS, but I looked when I went up to the yard today and only the front and the back have ABS.

Another problem: The chamber, sorry I don’t know all the names, on the wheel where the piston is has a leak. I know about the monster spring inside, so I’m not going to do anything I’m not sure of. But, all my brakes are caged, probably because my truck was towed onto the auction lot. I have Googled the issue and talked to mechanics and I am about to uncage them. Question: if I leave this one caged, can I open it up and if I do, is there anything I can do to fix the leak?

 

[davo727]

Get an air brake mechanic to change the 8 dollar rubber diaphragm in the leaking can and have him check the rest of it over and uncage and put everything back to normal status.

 

[KaiserM109]

Get an air brake mechanic to change the 8 dollar rubber diaphragm in the leaking can and have him check the rest of it over and uncage and put everything back to normal status.

Sounds like good advice, thanks.