Air In Lines Has Me At the End Of My Rope

[Gratefuldiver]

Ive been trying to bleed my rear calipers for a few months now and just cant figure it out or get it done. Everything is new at this point from the MC back. I have single diaphragm 9" booster with a 1" bore tandem Wilwood MC feeding a Baer adjustable proportioning valve which feeds a set of Wilwood D152 calipers in the rear all with SS 3/16" hardline (except short flex over the rear end and to calipers). I get fluid when I bleed but cant get rid of the air and the calipers don't bite down.

To start I bench bled the MC with the closed loop method till I had no air and couldn't push in more then a 1/8" with everything I had. I then pressure bleed the rear line unhooked from the MC and rear calipers to prime it of all the air. At this point I hooked everything up and had working rear brakes but the pedal felt spongy so I let them gravity bleed for a few hours but noticed I was getting a constant stream of small champaign bubbles even after running 500 ml of fluid through. I then decided I try the old two person method but am getting the same results. In fact it actually gotten worse as the calipers would even bit down anymore.



Its the same thing every time, when I first open the bleeder in nice solid fluid, then after about 2-3 sec the air starts. Long open times, short open times all the same. When I gravity its a steady stream of tiny bubbles. Id say Ive pumped over 2-3 liters of fluid through the back and cant get rid of the air and cant find any leaks. Ive even pulled the inner fender to check all the fitting to be sure I don't have any leaks. Ive tapped every inch of the MC, lines and calipers to clear any trapped air, let it gravity bleed all day long as I just kept cycling the fluid back into the MC so it didn't go dry, and did the two person thing to the point no one will answer their phone anymore lol

Anybody got anything? How can I be pulling air and not have a fluid leak? Would adding a few drops of glow from glow sticks and using a backlight help find a tiny leak I cant find otherwise? This isn't rocket science, its bleeding brakes, it shouldn't be this hard

[a67]

I went through this just a few months ago. Four wheel disc and a lousy spongy pedal. Bled the system multiple times via suction, pedal pumping, gravity, then went around and around and the pedal never changed. By plugging the M/C ports I was able to track it down to the rear brakes.

In the end I pressure bled them and finally got a decent pedal. Same as your car, a nearly constant stream of tiny, nearly invisible, air bubbles for quite a while. Pumped 3 gallons or more of brake fluid through before they stopped (re-cycled it).

To pressure bleed I used a garden sprayer and converted it. Used 15 psi from the compressor to power it. The output of the bleeder attached directly to the brake line at the M/C. That is, disconnect the brake line from the M/C (plug the port), and attach the pressure bleeder to the line. Then bled the rear calipers.

The brake line set up is different in this car. The stock combo valve is gutted and the switch port along with the divide between the front & rears is plugged. It is nothing more then a distribution block.

There is an adjustable proportioning valve in the rear line just off the M/C.

My guess is that it was the combo valve that was the issue. Way to easy for air to be trapped in it. The rear brake line comes in the top, with the out line exiting the end. So there is a chamber where air can sit in the top of.

Also, think of this, when gravity bleeding there is no way to really get all the air out (gravity is good for changing fluid in an already bled system). Vacuum bleeding, forget it, the air will expand into larger bubbles and won't move down the line (although good for changing fluid). Pedal bleeding, just takes too much pumping to move a large volume of fluid. Then each time the pedal is lifted it can pull air back toward the M/C.

Pressure bleeding causes the air to compress into smaller bubbles. Which allowed it to move down the line and keep going (no pauses).

Bob

[Gratefuldiver]

Now that you mention it the "out" of the adjustable PV is on the bottom of the valve, so I could see how air could get trapped up there at the top. The way the hard lines are ran it would be hard as hell to move it so the "out" is on top, but I guess I will have to explore that. Maybe I have enough room to just flip it over, placing the "out" at the top. I planed on picking up a gallon of fluid tonight and pressure bleeding through the rear line again just as you mentioned, which is the way I did it before.

Anybody else have anything to add, Id love to hear it


Edit: So the first pic is how I have it now and I can see how air can get trapped in there like that. So I will try to flip it and mount it like the sec pic. Or at least bleed it inverted.

[Rick Dorion]

My most time consuming brake bleed jobs are when I have all new lines. In addition to pressure bleeding I tap the lines with a wrench to dislodge any micro-bubbles. That's my story and I'm sticking to it!

[Gratefuldiver]

I talked to Baer and they said they have never heard of having air trapped because the way the PV is mounted so I left it alone for now. I did pressure bleed about 2 gallons of fluid through the rear and half through the front last night. The brakes are hard when I don't have my vac pump running but feel a little spongy when it is but they do stop the rear wheels with the rear in the air. Im almost afraid to try the two person method once I could never get it before like that. Im going to take it for a drive tonight after work and see what I have. As for leaks I never found one drop of fluid from any fittings so it makes no sence why I cant do the two person method.

If all is well I hope to do the last auto x of the year here in STL. They are using the whole road course at Gateway and it should be a blast assuming I can make it.

[Skip Fix]

My Longacre brake pressure gauges have bleeders in the top as even they can trap air. My Hurst line lok trapped air for ever even tapping bleeding out of both sides of the Wilwood calipers.

[Gratefuldiver]

Finally fixed, seems driving it and rebleeding a few times after I drove it did the trick. That was after I bench bled the MC closed, triple checked the adjuster rod, and pressure bled about 2 gallons of fluid through the rear. I found this chart and thought I add it, pretty much nails it right on the head