No brake fluid coming to the rear

[rickseeman]

I don't know brakes so I'm going to have to beg for help. This 70 Road Runner hasn't been on the road in many years. We put on a new master cylinder and tried to bleed the brakes. I think the fronts bleed fine but there is no brake fluid going to the rear brakes. We replaced the rear wheel cylinders. I think the power brake booster is out because the brakes feel the same with the motor running or off but that I don't think that's our problem. I'm thinking maybe one of the brass blocks underneath the master cylinder. (Whatever those do.) What do you think the point of failure would be? Surely someone besides me has had this problem trying to wake one up. Thank you.

 

[WileE]

Brass block = proportioning valve. It regulates the rear hydraulic pressure. Could be stuck.

 

[493 Mike]

My money is on the rear brake hose (body to axle). They tend to collapse/plug up with age. Crack open either line into the "Y" under the vent on the axle housing to check for flow. If none, break open the steel line fitting leading to the hose. Still no fluid, go right to the distribution block under the master cylinder.
Mike

 

[LowBikeMike]

Did you bench bleed the master cylinder? Have you checked for fluid before the rubber hose at the rear axle?

 

[rickseeman]

I think it has 2 brass blocks. Is one more susceptible than the other?

 

[rickseeman]

Did you bench bleed the master cylinder? Have you checked for fluid before the rubber hose at the rear axle?

The first time I didn't. That didn't work. So, then yes. But have not checked the rubber hose. That sounds like a good plan.

 

[dadsbee]

If it has the Hayes single piston, wide opening caliper, and the dual valve blocks + the differential valve further down the rail you need to get the fronts bleed and out tight and then have someone really stomp on the brake pedal and bleed them old school. You'll never suck it through...

 

[rickseeman]

Yes, it has the single floating caliper. All that stuff sure looks complicated to me.

 

[dadsbee]

You said you had the two "brass blocks" under the master. Just clarifying if this is what you have, as I show above, with the distribution block, metering valve and then the pressure differential valve further back on the drivers frame rail??? If so, get someone in the car pumping the pedal old school, like my Wife did for me. Hold to the floor and crack a bleeder, tighten bleeder and release... repeat as many times as it takes.. You also need the rear shoes out tight against the drum to do it right.

 

[rickseeman]

The pedal basically doesn't move. There is about 3/8"-1/2" of free play and then almost no movement with pressure.

 

[Rishi]

Make sure you're opening the zirk-nipple fitting at the rear drum enough to flow. The fitting from which the brakes are bled. Cracking it loose may not be enough. In fact, maybe scrub the surrounding area with a toothbrush, and completely remove the fitting and clean it, to confirm there isn't a clump of something behind it causing blockage.

 

[R413]

Make sure you're opening the zirk-nipple fitting at the rear drum enough to flow. The fitting from which the brakes are bled. Cracking it loose may not be enough. In fact, maybe scrub the surrounding area with a toothbrush, and completely remove the fitting and clean it, to confirm there isn't a clump of something behind it causing blockage.

The technical name is "bleeder screw".
Yes remove the bleeder screw amd make sure it is not plugged.

 

[rickseeman]

I will try that but I did have both of them backed off pretty good. But I'll try anything.