dewclaw

I am having a continuous problem with my brakes. I will describe then ask my question.
I noticed that my pedal started going halfway down before the braking would start. I found a leaky rear cylinder which I replaced. Bled the whole system. The pedal problem was till there . I replaced the master cylinder , bled the whole system again , the problem was still there. A local shop looked at it said it was bled properly and told me I had a bad ( new ) master cylinder. I put on another one ( new not rebuilt) . SAme problem . I SUPER bled the system with a vacuum bleeder set up . No help .

I did note that my power steering fluid was a little low, but the steering worked fine. I topped it off and the hydro boost brake system worked a "little" better .

Question , can my hydro boost system have an internal leak , like into or out of the accumulator which would cause the problem I am having ?
I have NO external leaks on the hydro boost or the brake system

HELP ME OUT here ! Im at my witts end .

THanks ,

Dew.

patdaly

You did make sure your rear brake shoes were adjusted out correctly, didn't you?

dewclaw

Yep , I read about that here , I adjusted them up in the rear twice, they are right up to the drum, slight contact .

I may disconnect the brake line from the rear and plug it to see if my problem is in the rear or front .........

patdaly

Ok, next do you have RWAL or 4WAL? If you have front ABS sensors, it is 2 wheel.

I take it you have no issue with the brake or ABS lights coming on when you push the brake pedal?

Another possibility is a flexible brake line being weak and bulging, though they usually blow out pretty quickly after they start. Might be worth it to have someone pushing the pedal while you watch/feel the lines.

dewclaw

I believe that i have RWAL, I dont recall now , if this truck has front sensors... I will look this afternoon( im at work now )
The brake lines all look good. No bulging with brakes depressed.

Heres a weird thing , the brakes are usually fine when its cold, then after about 5-10 minutes it starts happening. When it startes happening , its not everytime , probably 75 % of the time .
And if you give them a pump , the pedal goes right where it needs to be .
THANK YOU for taking interest in this . Bow season starts soon , I need to get the ol girl ready for the mountains.
DEW

dewclaw

Oh and , no brake or ABS light showing up.

dewclaw

PAtdaly , I have RWAL. I hope youre still out there.
MAn there is very little info on this on the internet !
I did find one write up that sure is pointing at what They call the EH valve ( electro hydraulic valve )
It sure makes sense that this is it BUT, there are two components just down stream of the master cyl. They both have an electric plug on them. This 1st one, ight off of the M.C. has one plug . The second one has two electric solnoids. I assume that this is the E.H. valve . This would be a major component in the RWAL. Am I correct ?
Are you still there PAtdaly ?

DEW

patdaly

Yea, sorry I was stumped. I have had the same thing happen on both of my RWAL trucks, and yes, it was that component.
BUT, the big difference was I had almost no braking when it messed up, and my Brake and Antilock lights would both come on. I suppose it could be leaking a minute amount past the seal into the accumulator, but I would not bet on it.

When you have the issue, can you quickly pump it and have the second or third stroke stop at full pedal ht.? If you hold the pedal, does it continue on down slowly?

Gotta say, your description does not match anything I have ever seen or heard of........

BTW, the first unit with the single plug is where your brake light switch is, the unit with the solenoids is the RWAL valve, called by various other names.

dewclaw

Yes , I can pump it up for solid braking . Usually just one or two pumps. If I hold the pedal, it does not continually go down.

I think that I am going to carefully take the RWALvalve apart and clean it thouroughly. Someone here did that with success.......

dewclaw

Ok, well Im narrowing this tihing down. I gently completely dissasembled the RAWL valve, and reassembled/reinstalled, did the super bleed of the rear brakes ( got plenty of air out . Still the same problem. About the only thing left is the proportioning valve and the hydro boost . I am leaning towards some sort of internal leak on the hydroboost (behind the master cyl.)
Could the proportioning valve give me this sort of problem ? I cant imagine why it would. Any opinions here ? Hydroboost ? or ? The power steering works fine...
Any input or thoughts ?

DEW

totalloser

God, your description sounds just like a bad master cylinder. I did read you replaced it already tho. And even then it's unlikely because usually one u-cup seal on the piston goes bad first causing an imbalance that trips the hydraulic balance sensor and makes your brake light come on. The only way I could see it not tripping the sensor would be if both seals were leaking at once which is unlikely in two separate m/c's

I don't *think* the proportioning valve could do this since it can only divert flow from one circuit to the other, thus it shouldn't be able to create any slop or sponginess, though it could transfer it upstream (like air in lines, brake adjustment etc.)

Here's a thought though. Maybe you have a caliper hanging up. If it's hanging up on one of the guide rods, it might shift slightly sideways from pad drag. When you pump the pedal it straightens out and firms up? Sort of a wild guess here.

Junk Man

Did you bench bleed the master before putting it on? I had an 85 Mercedes SD that required bench bleeding. I ran about 3 gallons of fluid through the system & still had spongy brakes. Removing MC & bench bleeding fixed it.

dewclaw

I bench bled both of the new master cyls.

Could be a caliper sticking .

I AM SO NEEDING TO GET THIS THING FIXED THAT i THINK i AM GOING TO BREAK DOWN AND GIVE IT OVER TO A GOODYEAR SHOP IN TOWN. (oops caps)

I have a caliper in the front that has been a tiny bit sticky for years , i will have them change both calipers while they are at it.

I sure hate paying for my stuff to be worked on but , between work and Deer season starting here I need to get this fixed. I will be SURE to let you all know what they find. I suspect that they will just start chaging parts out , I hope they are better than that .

Thanks for all the input
DEW

dewclaw

OK, so I just couldnt stand the thought of shelling out the bucks for someone else to figure this thing out .
This morning I plugged off the rear brake line at the master cyl. just to eliminate the possibility that the problem is in the rear brake circuit. ( RWAL, proportioning valve, improperly bled, etc) Well the pedal goes half way down MUCH less but it still happens. SO, It has to be either the MAster cyle ( I have already put two new ones in ) the front calipers, the hydro boost or the power steering ( which supplies pressure to the hydro boost).
The power steering is fine, it almost cant be the master cylinder.
SO , I ordered a new hydro booster and I picked up new front calipers ( one of them has been sticky for years and one of the bleeders is messed up so I wanted to replace them anyway ) I just need to find the time to install these items.
I recently moved out of my home so my tools are not with me : (
DEW

dewclaw

Ok , so I replaced the hydro boost and the brakes now work perfectly !!! HAppy camper . !!
BUT now the brake lights are on all the time .

Does anyone know how to adjust this switch . I had to use the old push rod ( as suggested by the instructions in the box) which was a lot closer in length that the one that was supplied, but not perfect .
How do I adjust the brake light switch . I will go on an internet search for the answer here first though . This is a GREAT site for answers ! Thanks for the help thusfar !!

DEW