brake issue... could it be the proportioning valve??

[gildardo01]

so, im working on the brakes on my truck and i just cant get the rear brakes to bleed, the front are great, good pressure and everything... but the back i can barely get a few drops of brake fluid... some one told me it would be the proportioning valve could this really be it? any suggestions?

[howlinwolf]

sounds like it. had the same problem. sometimes the piston sticks. I actually disassembled mine and cleaned it, and it works great now

[gildardo01]

sounds like it. had the same problem. sometimes the piston sticks. I actually disassembled mine and cleaned it, and it works great now

seems like i should start from there, because the only place i can buy one from is online... i know there is a piston like mecanism inside, and there should be about 3 o rings i supposed... did you reuse them?

[gildardo01]

i just took it apart and the piston inside is stuck... decided im going to let it sit for a while in mystery oil until it loosens up hopefully....

[81_Chevy]

another trick is to always bleed the backs first, that way the fronts dont get the piston stuck. same thing happened to me.

[Captkaos]

The backs should always be bled first, and on trucks it should be the rear passenger side...

[Blazin]

Agree on backs first. Should always bleed the one farthest from the master cylinder first, and work you way to the closest one to it.
I have only ever replaced one proportioning valve in all the years I have played with these trucks. That was on Yellow Snow the first week I owned it. Probably could have fixed that one but I had a good used one right handy. Reason that one stopped working is because the previous owner had put ATF in the master cylinder. Had allready replaced that, and both front calipers. Bout a month later had to replace both rear wheel cylinders, and do away with the load proportioning valve too!

[howlinwolf]

i dont think i have a load proportioning valve...  on the rear brake line, was that solid all the way back on stock trucks or two piece?
i ask because when i installed my new lines, the rear one was a two piece.

[Captkaos]

On 1/2T trucks the flex line was one piece, is that what you are asking, on HD trucks of 3/4T up it would have the load sensing valve...

[howlinwolf]

sorry, i should have specified, i meant the hard line from the proportioning valve to the rear hose

[gildardo01]

hey there... so i got it all cleaned up yesterday and the orings were in good shape.. the only thing that was in bad shape was the large seal the goes where the brake fluid exist for the rear breaks.. i replaced it with 2 orings r16 the ones that come in a kit at northern supply store... sealed nicely.... anyways i installed it this morning and it was still the same... just canīt seem to get pressure for the rear lines... i checked the master cylinder and i get very low pressure for the rear brakes.. i tried to bleed the master cylinder but more fluid gets sucked through the bleeding hose than coming out.. i know it shouldnīt be that way... what could be the problem... the master cylinder is fairly new...

fluid is just going back and forth in the hose and nothing is being bleed... why is this.. thanks

[thirsty]

Is this a truck that you regularly drive or is it a project that has been sitting?
Isn't there a reset button on these proportioning valves? Did you check the function of that? If that checks out open the lines at the wheel cylinders and check for good fluid flow. I just did battle with one of my wheel cylinders that had been in storage for a long time. They were new but installed and I packaged them up and stored them. Never gave a thought to moisture. They were junk when I put them back on. Just a thought.

[gildardo01]

Is this a truck that you regularly drive or is it a project that has been sitting?
Isn't there a reset button on these proportioning valves? Did you check the function of that? If that checks out open the lines at the wheel cylinders and check for good fluid flow. I just did battle with one of my wheel cylinders that had been in storage for a long time. They were new but installed and I packaged them up and stored them. Never gave a thought to moisture. They were junk when I put them back on. Just a thought.

no, i wasnīt a where of the reset function of the proportioning valve... but i was thinking why isnīt there enough pressure coming from the master cylinder, i took the master cylinder out and tried to bench bleed it again... well the part where the master cylinder send fluid to front brakes its great, very good pressure... but the other part, it sucks fluid in instead of shooting it out...  then it just goes back and forth... by the way its been a project for some time now.. and it has been sitting... i took the master cylinder apart and its all clean and everything inside...

[howlinwolf]

i would try the master anyway. its 25 bucks at oreillys

[gildardo01]

i would try the master anyway. its 25 bucks at oreillys

yeah i think thats what im going to do this weekend... i was reading about how high the failure rate is on these master cylinders right out of the box... why is this... master cylinders arenīt that complicated inside what makes them fail?