Diagram and Plumbing the Proportioning Valve

-

ecurb

Well-Known Member
Joined
Aug 13, 2008
Messages
139
Reaction score
10
Location
sonoma county
hello everyone,
what i need is detailed pictures of where to mount/postion the proportioning valve(PV) pictured here and how to run/where the brake lines go into the PV on a 68 barracuda with the 73-76 disc brake upgrade.
as always thanks in advance. bruce
 

Attachments

  • BLK250-46.jpg
    9.8 KB · Views: 654
BTW, yours is termed a "combination valve". It functions as: distribution block, proportioning valve, pressure imbalance switch, and front hold-off valve. I forgot the correct term for the last one, but you can find it in the links 67Dart273 posted.
 
Here's my advice. You need the proper documentation for these brakes. If you are using the 73/ later factory brakes, then go to MyMopar and download the 73 service manuals, and they are free Here is the combo valve pictorial, from page 5-19

propvalve.jpg
 
Here's my advice. You need the proper documentation for these brakes. If you are using the 73/ later factory brakes, then go to MyMopar and download the 73 service manuals, and they are free Here is the combo valve pictorial, from page 5-19

View attachment 1716262427
Thank u! That is what I was thinking, but on most of those valves I’ve seen that larger port at the top goes to back brakes.
 
Found this thread. OldManMopar is the MAN

 
Too funny. I was just going to post that. You might need to disassemble and clean or rebuilt it.
 
Definitely take an old one apart to clean and change seals. Unless the brake fluid was kept pristine, it likely has internal corrosion which keeps the pistons from sliding to function. Even on a simple drum-drum car where it is just a distribution block w/ imbalance switch, the piston for the switch is often stuck in place so won't give a dash-lamp warning.

Re optimal proportioning, that depends on all brake parts matching the year and configuration for the prop-valve. May also depend on the tires, and unlikely you would have bias-ply today. Even depends on weight distribution, as evidenced by the prop-valve on pickups and vans often having a feeler lever which senses rear sag to adjust the proportioning. Not needed on a sedan, unless regularly hauling bodies in the trunk (mafia). Optimal is that the front tires skid just before the rears, which you can test in an empty parking lot perhaps when wet (need helper to observe). An adjustable proportioning valve for the rear circuit makes that easy to adjust.

A prop-valve is usually for a Front disc - rear drum car. If yours has rear disks (never factory for old Mopars), I don't know if any aftermarket ones could adjust low enough to make the rear disks give proper braking (disks require more fluid pressure than drums). Without a prop-valve, the front-rear ratio comes from the brake parts used and there isn't the selection in caliper sizes like drum wheel cylinders allow. You can realize rear disks via either an aftermarket kit or modified Ford 8.8 rear (Explorer, many posts).
 
-
Back
Top