Brake system

[4spd69RR]

Have been working on my brake system and have replaced all my wheel cylinders. I am know trying to bleed the the lines. The problem I am facing is the brake fluid is not being pumped to the rear. The fronts bleed fine, however, not the rear. I am wondering if the proportioning valves may have malfunctioned. Wondering where to start first the front valve or the rear valve. Also if I have to replace one or both are these still available and easy to find?

 

[69hemibeep]

The small bowl or the front of the master cylinder goes to the rear. Is the master new and did it get bled?

 

[4spd69RR]

Yes it is new and it did get bled. You are correct thefront bowl is for the rear and the rear bowl is the only one I had to add fluid to. When the system is pumped and held, opening either rear valve nothing comes out. That is why I think the porportion valve may be causing my problem. Both valves are 40 year old and original. Is it more trouble to rebuild or just replace with NOS if I can find new? Does it make sense to remove the plug and verify where the internal piston position is? I'm thinking because of time and the amount of time this car sat in a garage, gravity may have caused the piston to drop blocking the proper flow of fluid. What do you think?

 

[69hemibeep]

Yes it is new and it did get bled. You are correct thefront bowl is for the rear and the rear bowl is the only one I had to add fluid to. When the system is pumped and held, opening either rear valve nothing comes out. That is why I think the porportion valve may be causing my problem. Both valves are 40 year old and original. Is it more trouble to rebuild or just replace with NOS if I can find new?

Mine cleaned up niceley but if your system gathered moisture like most do over time I would change it. Are your lines clean to the rear I like to shoot brake clean and compressed air threw them if they are old but not rusty. You might also open the line at the rearend splitter and see if your getting fluid to that point before you go and buy anything.

 

[cj69RR]

Crack the line off the back side of the proportioning valve and verify brake fluid there. Work your way back from there to Check for fluid and isolate your issue.

 

[moparchris]

Crack the line off the back side of the proportioning valve and verify brake fluid there. Work your way back from there to Check for fluid and isolate your issue.

Thats what I was thinking. I would start at the master though and work my way back.

 

[A31PKG]

The prop valve is nothing more than a calibrated restriction. If the pedal is hard when you bleed (and barring any other restrictions in the system) then it could be clogged somehow. If, on the other hand, the pedal goes to floor with no resistance and no fluid comes out (as you've stated) then I would suspect massive air somewhere as opposed to a clogged component.

 

[dutchrunner]

Try (if you haven't) with vacuum brake bleeder.
Not sure what's it called.

Cannister with hose to wheel cilinder and otherside to vacuum pump.

 

[4spd69RR]

So far I have fluid back to the rear splitter, I am getting to where it needs to go.

 

[69hemibeep]

So far I have fluid back to the rear splitter, I am getting to where it needs to go.

See if you have pressure to that point with a stab of the pedal and of course try and control the mess

 

[cj69RR]

Are you getting nice clean fluid under pressure to the split? Might be worth just building new lines back the rest of the way from there. Easy enough to do also.

 

[4spd69RR]

The problem I found is the rear hose from the brake line to the splitter, it is clogged. I have a new hose on order from NAPA and will pick it up tomorrow. The line from the splitter to each wheel cylinder is clear. To answer a different question from cj69RR about clear good fluid? I am getting clear fluid from the master down to the point of the rear hose. Thanks for the help gentlemen?

 

[Big John]

One thing...
If it's a drum brake car, that's not a proportioning valve. It's a switch that lights the dash light if you lose pressure in one side of the master cylinder.

 

[george68hemirr]

One thing...
If it's a drum brake car, that's not a proportioning valve. It's a switch that lights the dash light if you lose pressure in one side of the master cylinder.

thats the same thing i was having problems with on my 68 mustang......its a saftey switch/distribution block....like big john said if you blow a brake line and lose pressure on one side of the master you will still have brakes

 

[cj69RR]

Good to hear you found the issue. Better to find it than to throw parts at it. I would also check the condition of the front flexible lines to the front wheels also. Usually when one goes bad the others are not far behind.

 

[4spd69RR]

The the fronts brake lines were replaced several weeks ago when I replaced the front wheel cylinders. Just never thought about this rear line at the time I replaced the rear wheel cylinders.

 

[cj69RR]

You should be solid with the breaks and back on the road then.

 

[A31PKG]

One thing...
If it's a drum brake car, that's not a proportioning valve. It's a switch that lights the dash light if you lose pressure in one side of the master cylinder.

Big is right. I incorrectly referred to the safety switch body as a "prop" (proportioning) valve in my earlier post. It is not. The safety switch body serves two purposes, to provide a means for brake hydraulic failure warning, and to direct the fluid to the front & rear wheel cylinders.

As far as rubber brake lines go, if the inner hose ruptures, fluid can leak between it and the outer mesh/hose. When hydraulic pressure is thus applied, the leaking fluid squeezes against the inner hose causing either a restriction or to close up entirely. I replaced many rubber brake hoses back in the day for this issue...not much of a problem on modern cars.

Glad it's fixed!