m1009 brake issue

[remote6]

So I just replace my master cylinder on the M1009 because it was leaking. I bench bleed it and bleed the brakes but my brake light is on on the dash and the brakes are a little spungey. When I bleed the brakes hardley got any fluid out of the back, I bleed the system twice and a lot of pressure from the front. I just did some serching on here and read something about a proportioning valve? I never heard of this does it need to be bleed too? If so what is the process bleed the system then bleed the proportioning valve? Any info is great thanks Joe

 

[Anubis8472]

The proportioning valve reduces pressure to the rear brakes.
Without it your rear end would lock up all the time, as your front brakes have most of the weight and do most of the work.

I'm not familiar with the specific design used in these, though I'm sure it's in the TM's.

Some need to be 'reset', like a fuel cut-off.
That could be your issue.

Also make sure to check your parking brake. If it's not fully disengaged, or the pedal sags it will trip the brake light. (pull up on the parking brake pedal and see if the light turns off)

 

[Heath_h49008]

This might sound strange, but kick the brake pedal. I'm going to guess the proportioning valve has shifted fully and cut off fluid flow to the rear. Sometimes a few good kicks can pop it back to the centered position.

 

[remote6]

By kick do you mean stomp on it, I did read that in another thread I will try that tomorrow also the parking brake does appear to be up but I did not try to hold it up will also try that tomorrow thanks for the feed back!

 

[doghead]

Press it like you would in a panic stop. Not hard(and hold), just a quick stomp.

Might take 3 or 4 times.

 

[remote6]

Thanks, after I do that should I re bleed the brakes?

 

[doghead]

Probably.

 

[Heath_h49008]

If the valve was locked you probably didn't have enough flow to fully purge the rear lines.

Another trick to recenter the valve used to be blowing high pressure air back into the bleeder/line on the cut-off circuit.

Basically, you need some more pressure in the rears to push the valve back. Kicking it normally works. Air pressure if that doesn't.

 

[Barrman]

The "stomp on it" fix is about all there is for the proportioning valve. The -20 manual has a paragraph and picture of a tool that is supposed to be installed on the valve before any brake bleeding is attempted. I have never seen this tool or even heard of one for sale. It is actually more of a bracket that bolts on. It is probably easy to make too.

However, if you bleed real gentle like, it can be done without throwing the plunger over to one side. Colton and I replaced his rear wheel cylinders and shoes over the weekend on his M1009, RED and managed to bleed the system without causing the light to come on. A first for me. All my other square body trucks have had the light on when I was done. A few panic stop like pushes and all is well. You might see the light a time or two a week or so later, but another hard push and it will stay away until you actually have real troubles like it is supposed to tell you about.

 

[remote6]

Thanks everyone, I did do the hard push the other day a couple of times and the light went off. Brakes feel better but I will probably try and bleed the system again.

 

[Barrman]

If the pedal is firm, you don't need to bleed it. A sponge feeling means air. Low pedal but firm that can be pumped up is rear shoe adjustment.

 

[Keith_J]

DOT5 is higher viscosity than glycol based fluids and likes to trap air. I use a power brake bleeder (Motive brand) and have no issues with entrained air using DOT 5. On CUCVs, all it takes is 5 PSI at the bleeder jug to do all 4 wheels. And one quart. Now on a three axle FMV, two quarts and 8-10 PSI.

If you build your own bleeder, a 0-20 psi gauge is a must.