No flow/pressure in rear on initial bleed

[johnunit]

Finally got a chance to bleed the brakes on the vic today. Keep in mind literally everything hydraulic but the calipers have been replaced. Lines, master cylinder, rear wheel cylinders, everything. They're all new or off a known good car, but obviously neither is a guarantee.


Anyway, starting from an empty system and bench bled master cylinder, I let it gravity bleed. I got some fluid at the front calipers. I got none at the rears, at all. I closed the bleeders and went for the pressure (pump and hold) bleed, and have nothing at the rears at all after 6-8 cycles of pump and hold. No change in master cylinder level and I don't even feel a puff of air when I hold my finger over the bleeder and open it with the pedal depressed.

My next steps for tomorrow are to quadruple check all my connections and try to pick up a vacuum bleeder to try and suck the fluid out to the rears. I'm somewhat fearing a dead master cylinder though, which would be a real beyotch and expense to fix. I'm guessing I can eliminate the master by pulling the between the master cylinder and the distribution block and then depressing the pedal?


Has anyone had an issue like this before? Any theories? Could it be related to the valve/distribution block thing the lines go through under the master cylinder?

[Brown_Muscle]

I have a theory...Isn't there a check ball in the brake splitter/distribution bock that is supposed to move if you blow out a brake line, and cut off brake fluid to the line that blew? It could be possible this got stuck, this would especially make sense if you gravity bleed it, no pressure there to push the ball over the rear hole. You could try tapping it with a wrench...or take off the rear line going to it, at the block, like you said, and see if fluid comes out, at least this would confirm you are getting brake fluid to it. I would not depress the pedal to do this, as it would suck air back into the master cylinder, it should just flow out naturally.

Just another thing to note from my own experience. When i tried to vacuum bleed the rear brakes on mine, it would not work, IDK if that is related to the same check ball, or another issue (wheel cylinders sucking in air from the seals??)

EDIT: Oh also, does the pedal slowly sink and then bottom out? or is just really spongy and goes lower than normal? If it sink that would be a symptom of an internally leaking master cylinder, but since you have so much air in the system it will be hard to tell..

[johnunit]

I think there was at least some pedal feel coming in after the fronts, but we literally just pumped and then opened the bleeder once on each side on the front to confirm flow.

I was suspecting the dist. block too, so I guess that's my next step.

[slack]

I don't know if it helps but the distribution block under the master in my car only goes to my front lines. Top comes from the forward port on the master to the block. Back goes to driver's side caliper, bottom goes to passenger's side caliper. The line coming down in the foreground is the brake line to the rears that goes under the firewall and back.

Here's a pic:


Edit: I didn't know about the check ball. That definitely didn't happen when my rear wheel cylinder blew out. My whole master emptied out all over my rear drum.

[johnunit]

Weird. That's a different one than the one I had, and the one I installed from another car. Mine absolutely does connect to both MC lines and the 3 (rear + 2 front) lines. Do you have the metal capped master cylinder, or the newer one with the plastic reservoir and screw cap?

[slack]

Ah. That might be why. I have the newer master with the plastic screw cap. Didn't even think of that. Sorry.

[kishy]

If you have this valve with the old master cylinder, this actually has a reset button on the end of it to press when this happens. If that doesn't want to fix it, give it some gentle taps with someone playing with the pedal in combination with the button...

[johnunit]

Sweet. I would not have found that. Will check back in the next hour with results

[Brown_Muscle]

I did not know about that either! Pretty sure the ball gets stuck in the middle and do not operate as designed over time. it did not work when i blew my rear line either, nor did the brake light come on...lol. Good luck let us know if it works.

[slack]

I noticed that the newer one has a rubber "squishy" section in the back of it. I had no idea what it was and couldn't see it from above either. I'm wondering if that's similar to the reset switch of the older model?

Here's a pic of what I'm talking about:

[gadget73]

The rubber thing is the reset button. If nothing happens when you push the end, try tapping it lightly to see if it un-sticks. Its got a shuttle valve in there that stops up the open end of the system if something fails. Its also what is supposed to activate the red BRAKE light.

[johnunit]

Switch was stuck, the one towards the back of the car (near the lines for the front). Swapped for a block with that moving freely. Same issue. Brake pedal depressed, removed line going to rear brakes at dist. block and there is no sign of brake fluid at all at the fitting or in the line.

[johnunit]

Can I hold the rubber thing in while someone pumps to bypass? Seems my issue is as long as there is all air in the rears and some pressure in the front, it'll keep slamming flow to the rears shut. However, that two 25+ year old blocks have not let any fluid at all bypass seems very unlikely.

[jaywish]

Do you have one or two lines exiting your master?

If two, then fab up a short brake line run from the "rear" port which just dumps back into the reservoir. That will show what is being pumped out. Should be very strong flow.

[johnunit]

I THINK I ended up solving it, but I ran out of time to actually confirm by getting fluid to the rear wheel cylinders before the shop closed up for the night.

I pulled the line leading to the right front wheel, and the line to the rear, at the distribution block. This, in combination with holding the little button thing described, allowed fluid to finally spurt out of the distribution block where the rear brake line goes. I was then able to get flow from there again with the line to the right front tightened, but a front bleeder left just barely loose enough to let some fluid out. I could also feel the button/piston on the distribution block move outwards, meaning towards the part of the front lines. holding it back in allowed flow to the rear, confirming that it was the failsafe system restricting fluid to the rear. Leaving the bleeder open meant minimal pressure in the front, so no pressure differential.

Hopefully I can just bleed the rears with one front bleeder open, and then tighten up the rears and work on the fronts. MitchellOnDemand implies that the fronts are less sensitive and less likely to be blocked off because of the proportioning valving related to it being a disc/drum system. Fingers crossed.

Do you have one or two lines exiting your master?

If two, then fab up a short brake line run from the "rear" port which just dumps back into the reservoir. That will show what is being pumped out. Should be very strong flow.

I was sort of doing the same thing but messier, disconnecting the lines at the distribution block from the master cylinder, and confirmed good flow from both lines exiting the master.