no rear brakes

[76fomoco]

I am having a weird issue with my rear brakes. wilwood master and adjustable prop valve. I have fluid coming out of the rears when i bleed them, but i cant stop the rear tires when i apply the brakes. the shoes are adjusted out properly, I have adjusted the brake rod going into the master cyl which slowed but it still doesn't stop the tires. I have been running this setup for 2 years without an issue. no external leaks but when I'm not on the brake pedal i notice a few bubbles coming up in the rear section of the master.

 

[DirtDonk]

How old are the soft hoses in all locations, and the hard lines all along the frame and at the axle?
Could be a rusted-shut hard line or a goobered-up soft hose at the rear frame-to-axle drop.

And though I have not heard of any Wilwood proportioning valves having failed and shut down fluid flow too early, I suppose anything is possible.
You've tried adjusting the valve up and down so far? It's not supposed to reduce overall pressure to the rear brakes, but only supposed to come into play under hard braking to stop the pressure spikes that lock up rear brakes.
But anything in the line could be a potential blockage.

Also, you're sure they're correctly adjusted? How much scraping do you hear? How hard/easy is it to turn the wheels by hand?
How many notches of the parking brake does it take to slow/stop the rears?

Good luck.

Paul

 

[76fomoco]

the hard lines are stainless I did them about 10 years ago, I did the soft lines 2 years ago when I had the engine out for a reseal.

I didnt try the e-brake but will give it a shot this weekend. the shoes were loose before but in an effort to rule stuff out even with the drums being extremely difficult to turn without a tire on it hasnt made any dramatic differences with slowing the tires down.

I did adjust the proportioning valve all the way from most to least with minimal difference in stopping power.

 

[Apogee]

Given the fact that you're noticing air bubbles coming from the rear section of the reservoir (rear brake compensator port), my best guess would be that the seals are leaking a bit. To get air bubbles, it would have to be the external seal on the primary piston, but you would normally also see some fluid leaking at that point, so it's odd that you don't. If the internal seals are leaking or bypassing fluid, it would be internal to the MC and the fluid just returns to the reservoir, but you would notice the pedal sinking over time if you held it firmly for 15-20 seconds. Has the pedal travel or pedal feel changed at all?

Tobin

 

[76fomoco]

The pedal is very soft, it goes to the floor even after we bleed it out

 

[DirtDonk]

How are you driving it if it goes to the floor? What did you do just prior to this starting, or did it come on slowly over time?
If it goes to the floor, are your front brakes still working, as it sounds like you're saying? If so, then as you suspect it's most likely with the rear system only. But it's severe enough as to not let the fronts work to their full potential either.
When the front brakes do work, is the pedal spongy too, or does it just travel too far?

A few things I can think of that will cause the pedal travel:
1. Still too much air in the system (consistent with the bubbles)/
2. A mis-adjusted booster rod at the back of the master cylinder (if you have power assist of some kind?).
3. Too much travel in the brakes themselves at either end. Have to be WAY out of adjustment, but it's possible.

Does pumping the pedal result in any more firmness or higher pedal?
Definitely try putting on the parking brake (if it's not already) and if not already, try the brake pedal again once the parking brakes are applied.
Is this a GM conversion in the front and have you verified that you can still see daylight between the front caliper and the knuckle where it was ground down for clearance?
Sometimes they work fine for awhile, but as the pads wear you get interference that effects braking.

Paul

 

[surfer-b]

1: make sure calipers are on correct side
2: make sure front port on master goes to front and same for rear
3: make sure lines havnt got swapped at prop valve

 

[76fomoco]

1: make sure calipers are on correct side
2: make sure front port on master goes to front and same for rear
3: make sure lines havnt got swapped at prop valve

It’s all set up correctly thank you for the help

 

[Apogee]

The low pedal would seem to indicate air in the system, or a failure of some sort in the master cylinder. You could be leaking fluid around the internal seals on the piston for the rear brakes, which would cause excessive pedal travel and essentially little to no rear brakes since you're not generating pressure in that brake circuit. Fluid will still bleed, albeit probably not with as much pressure as it did before.

You can check the master cylinder by essentially performing a plugged-port bench bleed (on the truck or the bench), where you plug both outlet ports and then stroke the pistons until there's no air in the unit and it hydraulically locks. By disconnecting the brakes from the MC, you isolate the unit so there aren't any other variables in the system. Since your MC has been in use for a couple of years without issue, it should in theory already be bled and hydraulically lock pretty much right away, aside from whatever air you introduce into the outlet ports when installing the inverted flare plug fittings. If there is no air in the MC and the pistons still travel in the bore (slowly or quickly) when apply force to the piston, then the unit is passing fluid internally around the seals which is returning fluid up into the MC, thus little to no pressure in one or both of the brake circuits. While you don't know necessarily which seals internally are leaking, you do know that you need either a new master cylinder or a rebuild kit for the one you have. IIRC, Wilwood doesn't sell rebuild kits anymore and requires that you return the units to them to be rebuilt at Wilwood by their techs.

Tobin