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I'm not sure there is a -34 manual for the M939. I haven't found one anywhere or any reference to one. The -24 manual pretty well covers everything and is more in depth than the -24 manuals on other trucks. I tend to think they put all the info in the -24 for this series.

I finally figured out what the problem was. First off all the brakes were bad out of adjustment. The main problem though was a maxi chamber screw up on the drivers side front tandem. This wheel just happened to be the one I jacked up and was having the problem with the spring brake not applying...

They have a "star" nut type adjuster on the plungers that contact the shoe. Kind of like an old pickup hyd brake adjuster. TM says you need a tool but it looks like a flat bladed screwdriver would work. Doesn't look real easy to do through a small hole in the backing plate. I wish they had...

The M939 trucks have two chambers per wheel,not just a double chamber. One chamber is a single and is for the service brakes. The other chamber is a double chamber with spring brakes and is for emergency/parking. I think that is where some people are getting confused about the problem I'm...

Shoes appear to be brand new. The service brakes work fine. I guess the pistons could be stuck. It seems if they were to stick from sitting they would be stuck in the "on" position though. Yes, both chambers are used. On the front of the axle there is a maxi (spring) chamber. On the back...

The maxi chambers are indeed there. All I can figure is somebody adjusted them off so they wouldn't work. By looking in the hole where the caging bolt goes the chamber is applied but the brakes aren't. I've fooled with air brake trucks all my life but I've never worked on wedge type before. I...

I figured they were like all other brake chambers I've been around. All I've seen you have to insert a bolt into the hole in the back and tighten it to cage the brakes. Are you saying these are different? There is no bolt inserted in the back. I'm trying to find the -34 manual to try and get a...

No.

I just picked up my M936 from GL today. Everything works fine except the spring brakes. I can't get them to operate at all. The funny thing is they are in the released position. In other words, with zero air pressure in the truck the spring brakes are still released. Working the parking brake...