Can't bleed air out of rear brakes

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dartslantsix

dartslantsix

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I've got an odd issue with my brakes. I can't seem to get all of the air out of the rear brakes. I'm doing the 2 person pump brake method. I thought we had all the air out, so I went to the fronts and they bled like typical. Pedal went half way down, so we checked the rear again and more bubbles. Now it seems like the bubbles never end. No visible leaks. Sometimes when my wife pumps the pedal, a lot of fluid comes out, sometimes very little.

Set up is: Aluminum master cylinder (rebuilt, just installed), SSBC adjustable proportioning valve, late model discs in front, drum brake distribution block, and Ford rear discs (Explorer axle).

I've tried holding the rear calipers up and shaking to make sure they are the highest point, doesn't seem to matter.

I'm wondering if the master I got is bad- that seems to happen to a lot of people.

What do you guys think?
 
I blame the ford parts... ha.

Get the cheapo power bleeder at harbor freight, try it.
 
Is the rubber hose above differential new ? If there is a hose or fitting allowing air to enter, standing pressure will reveal it although bleeding procedure may not.
Years ago we were working on a Pontiac called The Judge ( I forget year model ). Anyway, that car sat with a pressure bleeder hooked up for more than half the work day before a tiny hair line crack in a caliper casting was revealed.
That sounds as if air would go in a lot easier than fluid would come out, but actually air was going both in and out. Only the pressure bleeder eventually pushed fluid out.
 
RedFish said:
Is the rubber hose above differential new ? If there is a hose or fitting allowing air to enter, standing pressure will reveal it although bleeding procedure may not.
Years ago we were working on a Pontiac called The Judge ( I forget year model ). Anyway, that car sat with a pressure bleeder hooked up for more than half the work day before a tiny hair line crack in a caliper casting was revealed.
That sounds as if air would go in a lot easier than fluid would come out, but actually air was going both in and out. Only the pressure bleeder eventually pushed fluid out.
Click to expand...

some one chime in here, but I thot that you didn`t need a porportioning valve w/ discs at both ends! Iv`e got 4 wheel discs on my build, and didn`t use one and my brakes seem fine after bleeding, alltho I haven`t driven it yet due to the build not being done.-----------bob
 
The proportion valve is for controlled braking. The front brakes get first fluid to create a nose down attitude, then the rear brakes should lock up. This is why early antilock brake systems were rear only. The fronts aren't supposed to lock anyway.
Bottom line... without the controlling valve you really don't know what the brakes will do in a panic stop situation.
 
Try using shorter strokes (travel) of the pedal.
Sometimes with long strokes the wheel cylinder will suck air in around the piston cups.
The power bleeders are a great solution because they force fluid the opposite direction causing those cup seals to flare/seal and push the air bubbles up and out to the master cylinder (the direction the air wants to go anyway) :)

The Fords that have the slave built into the throwout bearing are a real SOB to bleed without a power bleeder, because they have a larger hose and the air tends to want to go up the hose instead of down and out the bleeder valve.
 
I had this problem on an explorer that a customer did his own brakes on.he brought it in with the same complaint,Turns out he did his own calipers and mounted them on the wrong sides ,putting the bleeder below the brake hose.this was an '03 with a drum p brake.I don't know what setup you used though
 
Leave your friends alone. Run a tight fitting tube from the bleeder screw to a mason jar half full of brake fluid with the end of the tube submerged. Then pump your brakes a few times. It bleeds the air out and the fluid gets drawn back in. As said. bleed the MC first.
 
I am with Leadfoot, but also add a bit of dielectric grease to the external treads of bleeder screw. They can leak vacuum there. I use my hand and arm on the pedal, easier to tell what is happening at master cylinder. It also saves me from getting in and out of car.
 
did you bench bleed the m/c?
does the new the new p- valve have air in it?

I would start with the m/c-- if bench bled-- then move to the p-valve you installed.

pump your brakes & crack the line loose going to the rear-- see if air is present there.

if not continue to the rear system-- are the bleeders pointing up?

if nothing else fill the m/c & open the bleeder valves on the rears & gravity belled them for an hours-- to see what happens . Lawrence
 
Thanks for the responses, guys.
To answer the questions-
Rear hose is brand new.
Bleeder screws are correctly positioned (made that mistake a couple years ago and won't forget now)
I didn't bench bleed the master, so I'll do that this weekend and report back.
 
Okay... I bench bled the master cylinder and tried bleeding the rear calipers again. Same problem.

So, I started disconnecting things starting at my adjustable prop valve. When pumped, just a gurgle of fluid came out. I continued removing pieces up to the master cylinder port- just a gurgle of fluid comes out when the pedal is pushed. Should be a solid stream- so I just ordered another master cylinder.

Hopefully this will be a good one.

Thanks for everyone's input.
 
Standard hydraulic brakes do not need to be pumped to be bled. Gravity bleeding actually works best. You need to bench bleed the MC as outlined. One of the most important things that hardly anyone ever thinks to do is to bleed the system with master cylinder LEVEL. This is extremely important. Most times the MC is angled upward at the front and will trap air in the end of the cylinder. You need to jack the car up so the MC is level. Then starting from the RR gravity bleed until solid fluid comes out. Proceed to the LR, then RF, then finally LF.
 
RustyRatRod said:
Standard hydraulic brakes do not need to be pumped to be bled. Gravity bleeding actually works best. You need to bench bleed the MC as outlined. One of the most important things that hardly anyone ever thinks to do is to bleed the system with master cylinder LEVEL. This is extremely important. Most times the MC is angled upward at the front and will trap air in the end of the cylinder. You need to jack the car up so the MC is level. Then starting from the RR gravity bleed until solid fluid comes out. Proceed to the LR, then RF, then finally LF.
Click to expand...

Yep, I just crack the bleeder screws and remove the MC caps and let them drip for a bit. At first nothing might come out but give it some time and watch them bleed
 
68cuda408 said:
I had this problem on an explorer that a customer did his own brakes on.he brought it in with the same complaint,Turns out he did his own calipers and mounted them on the wrong sides ,putting the bleeder below the brake hose.this was an '03 with a drum p brake.I don't know what setup you used though
Click to expand...

X2^ did the disk brake conversion on my demon using 79 volare calipers and couldnt get the fronts to bleed. Turned out the bleeders were on the bottom and was creating a cavity of air above them but due to the brake hoses i had to leave them mounted where the bleeder was on the bottom so i just took the calipers loose turned them to where the bleeder was on top then put a 2x4 in the caliper and bleed them that way. Problem solved
 
Mighty vac in the calipers using that rubber cone fitting. Suck em slowly bubble free, then add the bleeder and hose and do it again. Pull a light vacuum and just barely crack bleader, then close again.
 
When you say that you bench bled it; Did you in fact take it off the car, put it in a vise (nose slightely down), use the little fittings and hoses that usually come with the new m/c, and with the hoses submerged in the fluid, and stroking it full length and releasing the piston to allow it to return to the snapring stop?If yes and it wont quit sending bubbles then its probably defective. If you attempt to benchbleed it on the car(nose down) then you have to be sure that the piston is returning to the parked position. If it hangs up or the pushrod is improperly adjusted/seated then the compensating port may not open. In this case it will never bleed and neither will the next one. So;be sure the compensating port is open and working.
 
71DodgeDemon340 said:
X2^ did the disk brake conversion on my demon using 79 volare calipers and couldnt get the fronts to bleed. Turned out the bleeders were on the bottom and was creating a cavity of air above them but due to the brake hoses i had to leave them mounted where the bleeder was on the bottom so i just took the calipers loose turned them to where the bleeder was on top then put a 2x4 in the caliper and bleed them that way. Problem solved
Click to expand...

why didn't you just swap them side to side?most calipers without p-brakes are symmetrical with the exception of the hose locating boss which can easily be removed if needed.
 
RedFish said:
The proportion valve is for controlled braking. The front brakes get first fluid to create a nose down attitude, then the rear brakes should lock up. This is why early antilock brake systems were rear only. The fronts aren't supposed to lock anyway.
Bottom line... without the controlling valve you really don't know what the brakes will do in a panic stop situation.
Click to expand...

Ummm, if I'm reading this correctly, you're fundamentally wrong. You want the fronts to lock, and the rears to never lock.

Rears lock=spin.
 
RustyRatRod said:
Standard hydraulic brakes do not need to be pumped to be bled. Gravity bleeding actually works best. You need to bench bleed the MC as outlined. One of the most important things that hardly anyone ever thinks to do is to bleed the system with master cylinder LEVEL. This is extremely important. Most times the MC is angled upward at the front and will trap air in the end of the cylinder. You need to jack the car up so the MC is level. Then starting from the RR gravity bleed until solid fluid comes out. Proceed to the LR, then RF, then finally LF.
Click to expand...

Yep what he sssssssssssssaid been there done that.
 
As an update to this thread, I returned the master cylinder I was working with and got another. Bled it on the bench and it's working fine now. The first master I got was apparently bad and the front port was not working.

Thanks again.
 
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