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.

 

[Runner 68]

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...
View attachment 1767233View attachment 1767235View attachment 1767236View attachment 1767237

Never get tired of that first pic of your wife photo bombing Dad. At least I assume so. Daughter perhaps?

 

[dadsbee]

Never get tired of that first pic of your wife photo bombing Dad. At least I assume so. Daughter perhaps?

Wife pumping the brakes...

 

[Runner 68]

Wife pumping the brakes...

She looks too happy to be doing that task.
Bleeding brakes with the spouse has caused more than one divorce.

 

[moparedtn]

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

@rickseeman - I agree with Mike here.
Did you see fluid out of the metal lines at the wheel cylinders when you swapped them?
If yes, then start at the tee on the rear axle and work your way back towards the front of the car, checking
at every joint for fluid until you hit something dry/clogged.

 

[MoparLeo]

Right off the bat you did something that I wish more members would do. It would save a lot of guessing and maybe even your life.
You said that you don't know brakes.
Like someone saying I am not a surgeon and then asking how do you sew.
First, before you start spending money.
Find yourself someone who is proficient in brake systems.
Get your self a copy of the Factory Service Manual. I will give you a link for a free download.
Get yourself a book on brake systems. Educate yourself you have an understanding of what is happening.
This is the most important system on any car. If the brakes fail, people can get hurt or die so don't mess around.
Have the entire brake system inspected by a certified brake shop.
Better yet, the car is over 50 years old and has been off the road. Dot 3 brakefluid is hygroscopic. It absorbs water. Water contains oxygen. Oxygen allows oxidation better known as rust.
The corrosion occurs internally. You cannot see it. Here is my recommendation. It is not the cheapest but I value my life, safety and the car too much to try to save a few hundred dollars to risk injury and thousands of dollars in damage/injury.
Start with the Master cylinder and replace your way back. Only use a new Master cylinder, not a rebuilt.
This is the heart of the system and must be totally reliable.
Replace all brake lines . Metal and rubber. Avoid s/s lines as they are difficult to sea/seal against leaks.
All components are available new except for brake system valves, they can be purchased as rebuilt or kits are available if you trust yourself to do it. Use quality parts as they must work. It is always too expensive to go cheap. Think about that.

Service Manuals – MyMopar

 

[Geoff 2]

Also a good chance the brake line to the rear brake line is rusted internally....& blocked.

 

[dvw]

Loosen one connection at a time while your helper has pressure on the pedal. First at the master rear line feed. Then in order; the outlet of the first brass block, outlet of the second brass block, oulet of the rear rubber hose, rear bleeders. When there is is no fluid seepage at the loosened connection you've found your issue. I had siezed blocks, collapsed hoses (recently on a 68 B body), plugged bleeder screws. As long as the lines come loose its a quick diagnosis.
Doug