M1009 brake combination valve reset

[Barrman]

I try searching, but didn't find any answers.

I was driving the M1009 to work this morning. The plan was for my students to pull the front rotors, turn them and refresh the bearing grease. Some idiot pulling out of the taco stand caused me to do a crash stop. I missed them, but the brake warning light came on. I got to work with a low pedal and the drivers rear tire had fluid all over it. Once we pulled it apart, we found a popped piston on the wheel cylinder. The piston actually popped out of the cylinder.

The reason for the piston stop not stopping it was there was only 1 screw holding the cylinder on and that side had pulled away from the backing plate enough that it just shot the piston out. Also turns out Soldier A, firefighter B or forest ranger C put on nice new rear brake shoes. They just didn't adjust them. Therefore, the piston had to go way out to stop the truck.

We cleaned the cylinder and all its parts up, put it back together, turned the really warped front rotors and got all that back together. Once we bled the rear. We are getting very little pressure, the brake pedal is low and the light is still on. The combination valve has shut off the rear brakes.

I can't find the reset on it and the manuals just say "replace" when the combination valve is mentioned. Anybody pulled one apart to reset it, know the secret to resetting or if not, a place to buy new ones for less than the prices I am seing on auto store websites?

Thanks.

 

[blitzengine]

Barrman, DO NOT take the combination valve apart, you will end up breaking the needle in the combination valve and there are NO rebuild kits for them. The instructions state to have an assistant push and hold the needle in so that you can bleed the brakes or install a tool onto the combination valve that does that does this for you by holding the needle centered as you bleed the system. The tool that I am reffering to is on the link. http://www.costplustools.com/Kent-Moore-J-39177-COMBINATION-VALVE-BLEEDING-TOOL_p_7215.html Or you can make your own like the one described in the bleeding instructions on TM 9-2320-289-20 pg 7-10.


Hope this helps

 

[Barrman]

I was the tool in the -20 and read about installing it. I didn't because mine had already moved over to no rear brake mode. I pulled the rubber cover off the plunger/nut. The needle wasn't sticking out, I tried pushing it in with my finger and a screw driver, but it wouldn't move any at all.

The pedal really isn't that low with the engine running. Front brakes work great, so I drove it home and actually had good stopping. Rotors that are round make the stopping experience better. Once on my dirt road, I did another crash stop and only the fronts skidded. My Haynes Chevy manual says the same as the military TM's. Remove and replace.

I will go out once it gets below 98 or so and see if I can push the needle in some again. I wonder what would happen if I let the pressure on the fronts go? Would that send it back to the middle?

I have only messed with M35/M715/flat fender stuff super simple or the newer all electronic ABS systems for the last decade or so and am at a memory loss for these systems. Thanks for the help.

 

[NMC_EXP]

Barrman

I had to replace the combination/proportioning valve on my M1009. GM does not stock replacements but an outfit called InLine Tube has them in stock along with a lot of other brake parts for classic vehicles.

The unit visually looks good - machined from brass barstock. Had to swap the original switch for the one that came with the new valve as I recall (?).

Here's a link:

Inline Tube - Preformed Stainless & OEM Brake Line Sets

Regards

Jim

 

[Barrman]

The needle was still stuck in when I checked it last night. I had Colton push the pedal while I tried pushing the needle more. It didn't move.

I had to go to town this morning for some stuff and drove the M1009. Brake light on and a lower than normal pedal. I was hoping one of the auto parts stores would have something we could match up by looks. I made 3 stops and backed into parking spaces at each. While backing up the 3rd time, the pedal seemed to rise while I lightly pushed it. The best way to describe it is with a vacuum boosted car, the engine is off and you push the pedal. Then start the engine, the pedal rises. The 715 with its massive drum brakes feels that way all the time backing up, so I didn't even think about it.

I fired it up to leave and the brake light was out. I pushed the parking brake to make sure the bulb was still good, it was. I rolled forward and jumped on the brakes. High pedal that locked all 4 up. Problem is gone.

I don't know what caused the outwardly appearing to be in the middle combination valve to reset. Backing up, using the truck with everything adjusted, I don't know.

Thought I should post an ending.

Oh, O'reilly's called their tech support and tech support said to call inline tubing.