Need advice on brakes!?!?!?!?

[poolguy]

My 94 f350 brake pedal got lower and lower, so I put it in the shop this morning, and they've been working on it all afternoon!
Installed new pads on front, adjusted rear shoes, bled proportioning valve and 3 wheels. One bleeder broke off so bled the line at the fitting. I have watched the front calipers work, -looks normal- but the pedal still pumps up and then leaks down with nominal pressure on the pedal.
So I bought a re-man. (scary huh?) master cyl. Bled everthing again, and the brakes are the same as before any repairs were made!
I had to drive it home (no room inside the shop) and I really nursed it. I pull fairly heavy equipment with this truck and can't with the brakes like this. I could tell that the mechanic ( a good guy) is scratching his head.
Anybody got any idea what to do?
The truck has abs sensors on the rear end, but I didn't see an abs pump.
Thanks,
Chuck

 

[Diesel Fly]

What you describe - "but the pedal still pumps up and then leaks down with nominal pressure on the pedal." - is usually a master cylinder. Seems weird since you already replaced that. Did you bench bleed the MC before installing it? I'm assuming you already checked all of the obvious stuff (leaks, loose bleeders, etc.) Also, the pedal is not spongy right?

 

[poolguy]

What you describe - "but the pedal still pumps up and then leaks down with nominal pressure on the pedal." - is usually a master cylinder. Seems weird since you already replaced that. Did you bench bleed the MC before installing it? I'm assuming you already checked all of the obvious stuff (leaks, loose bleeders, etc.) Also, the pedal is not spongy right?

Sure did. I can't figure out where the fluid goes when the pedal sinks, but I'm not losing any noticable fluid. There was a brake line with pin holes to begin with, but that was fixed 1st thing.
I'm puzzled.

 

[yARIC008]

I'd say two things... Either the master cylinder you got is bad too, or your booster is going bad. Did they also replace all the flexible brake lines upfront? I hear they go bad on the inside sometimes and let the fluid in there. The lines are cheap and easy to replace. Did they also replace the calipers?

 

[poolguy]

I'd say two things... Either the master cylinder you got is bad too, or your booster is going bad. Did they also replace all the flexible brake lines upfront? I hear they go bad on the inside sometimes and let the fluid in there. The lines are cheap and easy to replace. Did they also replace the calipers?

I couldn't tell you if the booster was checked out or not, but the mechanic owns his own shop and has been in business for over 20 years. I can only assume he checked the booster.
With a re-man master cyl anything is possible. I'm sure the rubber lines were not replaced. Do they balloon or leak? I dont seem to be losing fluid.
Thanks,
Chuck

 

[metrojd]

Air in system

you said bled proportioning valve ?
Are you talking about the Rabs Valve?
I have had the same problem before and it was Air.
I blead and blead and thought it was ok.
But it was the same deal you have.
I wound up bleading the Hell out of it and all is fine.
Problem might be the wheel that the bleader is broke??
Is that a front?? If so I would say thats it,The line is lower that the bleader.
So there is a air pocket above the line.
Good luck
John

 

[84TD]

Do 94's have the vacuum pump? Maybe your vacuum pump is weak or there is a leak between the pump and the booster.

 

[hahn_rossman]

Your symptoms are typical of a failed RABS valve. It's located under the drivers seat. Maybe along the frame rail or somewhere similar. If you unplug it and your problems stop, your diagnosis is complete. Be prepared to be shocked at the price of a new one. Good Luck.

 

[towcat]

Your symptoms are typical of a failed RABS valve. It's located under the drivers seat. Maybe along the frame rail or somewhere similar. If you unplug it and your problems stop, your diagnosis is complete. Be prepared to be shocked at the price of a new one. Good Luck.

+1 on his take.
wanna disconnect the RABS on the frame and see what the pedal feels like?
betcha you're gonna be suprised.

 

[poolguy]

Could this be what I thought was the proportioning valve?

 

[kcw12]

Does a 90 have it?

 

[towcat]

Does a 90 have it?

If you have a electrical connector coming off the pumpkin housing on your axle, you have ABS

 

[poolguy]

The truck is a 94 and definately has rear abs. By the way the truck is back at the shop, and the mechanic now has the info on the rabs valve.
He did'nt know it was there, or how to check it. We'll see what happens next.

 

[icanfixall]

The RABS valve is costly but you can check Ebay for one. I paid $24.00 for a new one for my truck. Also set the emergency brake. If the E peddle sets more than half way down the rear brakes are not adjusted up properly. When the E brakes are set try pushing on the brake peddle again. Did the peddle come up and did it slowly drop down? If no to both questions you need to adjust up the rears. This is a common problem. The master cylinder can't push enough fluid to fill the out of adjustment rears and most times you get a sinking brake peddle trying to fill the rear cylinders AFTER the fronts have done all the stopping. The fronts often will overheat and crack or warp the rotors. They don't last very long either. The rears auto adjusters really don't work like they are designed to.

 

[kcw12]

If you have a electrical connector coming off the pumpkin housing on your axle, you have ABS

no electrical connections, so no abs