proportioning valve
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
proportioning valve
I noticed that my rear brakes aren't really getting as much pressure as my front ones. My front wheels are covered in brake dust. But the rears are clean. Also my rear rotor is still a bit dirty, and when bleeding my rear calipers, no fluid came out. My fronts work fine. My friend and I are guessing its the prop valve. A shop also just guessed(they specifically said I think) that I needed a new prop valve. Anyone know if this is the proportioning valve causing the issue and if so, does anyone know the thread for it? Thread for the master cylinder brake line. I'm looking into a new adjustable prop valve from summit. Any help would be appreciated.
Melting Slicks
Joined: Jul 2006
Posts: 2,285
Likes: 487
From: Salmon Arm, BC
I'd start by having a look at the rear calipers for leaks around the rubber boots and if that looks ok, try bleeding the rears.......wait a minute.....I just read your post again and you say no fluid out of the rears.
Try this....push hard on the brake pedal and bleed one of the fronts, that may re centre the proportioning valve.
Try this....push hard on the brake pedal and bleed one of the fronts, that may re centre the proportioning valve.
Last edited by OMF; May 9, 2012 at 12:21 AM. Reason: should read opening posters complete thread
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
If it has rubber factory style hoses on it, they can decay and collapse on the inside. You cannot see this from the outside... the outside can look perfectly fine. Collapsed hoses can cause your problem. The brake switch (prop valve) can also cause this. If it is stuck "off center" as a result of bleeding the brakes, opening the opposite side to atmosphere (in this case a front bleeder) and pressing hard on the pedal can sometimes re-center the pistons in the switch (prop valve). Just because it is stuck does not mean you need a new one. Don't waste your money or labor until you verify the real problem. The Summit valves are not a direct replacement. You would have to cobb up the lines.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
The rubber lines collapse from the inside. Just because you replaced the M/C doesn't mean it is adjusted correctly. The push rod has to be properly adjusted to uncover all of the vents, or it will do exactly what you are experiencing.
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Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
that's not a proportioning valve-it's just a switch that senses difference between the front and rear brake systems that illuminates the 'brake' lite. you've got a blockage somewhere. start at the back of the car and bleed each fitting (calipers and all block connections)until you get good fluid flow.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
77s have a proportioning valve.
First remove bleeders to see if they are blocked.
If bleeders good, then to test the rears, remove lines from the block beside the trailing arm, if fluid there, then the hoses are bad.
If no fluid there, remove the rear line from the proportioning valve and then unscrew the proportioning valve from the differential valve.
If fluid there, the proportioning valve is blocked or bad.
If no fluid there, then the differential valve spool is most likely off center. The dash brake lite should be on in that case.
Recenter the spool.
First remove bleeders to see if they are blocked.
If bleeders good, then to test the rears, remove lines from the block beside the trailing arm, if fluid there, then the hoses are bad.
If no fluid there, remove the rear line from the proportioning valve and then unscrew the proportioning valve from the differential valve.
If fluid there, the proportioning valve is blocked or bad.
If no fluid there, then the differential valve spool is most likely off center. The dash brake lite should be on in that case.
Recenter the spool.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
I tried some of those steps above. Still have to check the actual rubber lines and everything but as of now I tried bleeding the fronts then the rears. Fronts are good. Rears are not. Also somehow my brake fluid in the master cylinder went down before bleeding. The half closer to the booster was completely dry. Not sure if that half slot was for the rear brakes? Tomorrow I'm going to remove the rear calipers and lines. Fronts are new calipers. Rears are the same delco originals. I'll be trying the rest of the advice you have all given me hopefully tomorrow before class. Any update I'll report here.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
I refilled the master cylinder again last night. Tried bleeding the brakes a bit. Wouldn't seem to get anything in the rears. Left it alone for the night. Checked it a few minutes ago. It's depleted again. Not dry but just like really low. Maybe like at 15% capacity in the half closer to the brake booster. Could it be that the fluid leaked into the booster or that the fluid went to the prop valve and is in my brake lines?
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
The fluid is going to go to where the leak is. If a rear caliper is leaking, the fluid would go through the lines to the caliper and leak out there. If the leak is out the back of the master cylinder, then it's going to leak out there and nothing is in the lines to the rear.
You should remove the two mounting nuts from the MC, and pull it forward a bit so you can see if there is fluid coming out the back.
You should remove the two mounting nuts from the MC, and pull it forward a bit so you can see if there is fluid coming out the back.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
Found the problem. My rear calipers were both leaking. A lot. The fluid from last night was in the lines, just not enough to reach the calipers. Refilled the master cylinder. Started bleeding and all went well. Until the pistons started leaking fluid. Looks like ima need new calipers. Anyone have any suggestions on rear calipers? Or can I just go and buy 2 rears from autozone?
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Found the problem. My rear calipers were both leaking. A lot. The fluid from last night was in the lines, just not enough to reach the calipers. Refilled the master cylinder. Started bleeding and all went well. Until the pistons started leaking fluid. Looks like ima need new calipers. Anyone have any suggestions on rear calipers? Or can I just go and buy 2 rears from autozone?
Well, now you know a little more about how brakes work. First thing ya check is if the master cylinder has fluid in it. What concerns me is that if you had no fluid in the rear brake lines, the brake light should have been on, and you didn't mention that.
Keep the shiny side up!
Scott
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
Actually the brake light in the tach was on. I just always thought it meant the hand brake not the rear brakes. Learned something there. I'll be ordering some calipers from autozone on my next paycheck. Hopefully everything will be good with my brakes at that point. I didn't know the brake light was for the calipers and not the hand brake...lol oh well learned something there 
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
Do I absolutely have to bench bleed the master cylinder? Or will the trapped air just eventually bleed out the caliper after going through all the line?
Whats this about an O-ring conversion? I was thinking of buying remanufactured calipers from autozone for about $70(minus 20% employee discount) each. I'm curious about this O-ring thing though. What is it exactly? meanwhile ima do some research on it
Whats this about an O-ring conversion? I was thinking of buying remanufactured calipers from autozone for about $70(minus 20% employee discount) each. I'm curious about this O-ring thing though. What is it exactly? meanwhile ima do some research on it