Boogerschnot 12 Report post Posted January 25, 2013 So, I thought my master cylinder was bad.. Replaced it using the lifetime warranty through Oriley's. have pressure at the MC now but am trying to figure out what is going on with my differential pressure switch and my rear brakes getting no pressure. The day I decided to change a rear cylinder, I had locked up the rear wheels in a panic stop and when I got home the brakes felt a little more funny than usual. I found some fluid on my right rear wheel and then a leaking cylinder. Replaced it and when I tried to bleed it I found that I was getting no pressure or very little fluid movement at the rear wheels. The fronts work great. I am reading that some cars have a combination differential pressure switch/valve, and some may have a residual pressure valve for keeping pressure at the rear discs? My diff pressure switch looks like nothing in the haynes manual, or any other write up's. Please look at the pics and tell me what I have going on. I would love for my rear brakes to work again. thank god Im not using it as a daily driver now days. My little interpretation.. Quote Share this post Link to post Share on other sites
Boogerschnot 12 Report post Posted January 25, 2013 What do i have here? Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted January 25, 2013 I have no idea from the pic, especially if your proportioning valve is like your drawing. My prop valve is a cylinder about 3/4" x 5". If it's like most and hasn't been rebuilt in 44 yrs, it should be. Check out West Coast Classic Cougar YouTube's video on rebuilding a prop valve. Pretty simple rebuild, but pricy. I chose to ditch the stock valve and use a Wilwood adjustable valve. It cost $45, less than the rebuilt kit. Bob Quote Share this post Link to post Share on other sites
68stang289 26 Report post Posted January 25, 2013 I experienced a similar issue on my car so I have a few thoughts on helping diagnose the issue. 1. Crack the brake lines at the distribution block and then press the brakes (be sure you put a bunch of rags down to catch the fluid though). Are you getting fluid out of the lines there? If not, then you may have tripped the valve inside the distribution block. To reset it, I believe you lightly pump the brakes 3 times, and then slam down on the brake pedal. You should hear a click if you're doing that right. 2. If there's fluid at the distribution block, then you need to start cracking the brake lines along the way to the back and seeing if you have fluid coming out when you pump the brakes. For me, it ended up being the rear brake line hose that gets bolted to the rear axle. It was clogged up and was preventing the fluid from reaching the rear brakes. That should help you isolate the area where the issue lies so we can help you further. Quote Share this post Link to post Share on other sites
Boogerschnot 12 Report post Posted January 25, 2013 Maybe tomorrow Ill check the final output of the distribution block.. I know that is the next logical step, I think Im just lazy. I do have a new rubber line for where the rear end connects to the hard line at the 9inch. Ill check the dist. block and then the rear end to be sure its not a blockage. It still bothers me that this type of block and the reason for having it is not listed in the haynes manual, or in most writeups found anywhere.. Quote Share this post Link to post Share on other sites
68stang289 26 Report post Posted January 25, 2013 Are you running a front disc/rear drum or 4 corner drums setup? Quote Share this post Link to post Share on other sites
Boogerschnot 12 Report post Posted January 25, 2013 Front discs.. rear drums. Quote Share this post Link to post Share on other sites
frankenstang 11 Report post Posted January 25, 2013 I had the exact same issue on my '68 with disc/drum. Turns out the pin in the distribution block had moved. I was unable to recenter it no matter what I did. Ultimately I purchased a new distribution block and proportioning valve. Took me only a couple of hours to replace and fab new lines to the proportiong valve. Problem was solved and the brakes are better than they every were. Sometimes it is easier to replace than hunt and diagnose Steve. Quote Share this post Link to post Share on other sites
jmlay 80 Report post Posted January 25, 2013 What condition are your lines in, hard & soft? After 40+ years I would be replacing them all as well as rebuilding the distribution valve. Contact Scott at Muscle Car Research: https://www.musclecarresearch.com/ford-parts Mike Quote Share this post Link to post Share on other sites
Max Power 74 Report post Posted January 25, 2013 2. If there's fluid at the distribution block, then you need to start cracking the brake lines along the way to the back and seeing if you have fluid coming out when you pump the brakes. For me, it ended up being the rear brake line hose that gets bolted to the rear axle. It was clogged up and was preventing the fluid from reaching the rear brakes. That should help you isolate the area where the issue lies so we can help you further. I had the exact same problem. I did the reverse of you though, I started at the rear cylinders and worked my way backwards. Turned out it was the same distribution block bolted to the rear axle that you had trouble with. Quote Share this post Link to post Share on other sites
LoneWolf2U 136 Report post Posted January 25, 2013 With the light disconnected, I would check there first. Most likely the problem is the shuttle has been moved and closed off the rear lines. Yes its a pain to repair, but it is needed for saftey reasons. Quote Share this post Link to post Share on other sites
Boogerschnot 12 Report post Posted January 25, 2013 Thanks guys. Ill get out there and just chase the fluid back from the block to the rear. Wherever I dont have fluid should tell me where the problem lies. Hopefully its the rear block on the 9 inch. Quote Share this post Link to post Share on other sites
