brake repositioning valve problem???
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Freshman User
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From: oregone
brake repositioning valve problem???
As I stated in an earlier thread I having difficulties with a 76 f350 brake system. After parked for an hor the pedal went to nearly the floor; only the last 1.5 in of pedal had pressure, but was able to make it home. I replaced the master cylinder (MC) and the symptoms remained. I am attempting to bleed the system but can get no oil back to the rear brakes.
Another anomaly; when the brake pedal is depressed, fluid shoots up out of the MC, rather than when it is returned to the up position. It is bypassing somewhere.
In my nearly 40 years of driving ford trucks, starting with a new 73, I have never attacked the repositioning valve other than removing the lead to make the dash brake indicator light turn off.
Is that maze of brake lines the issue? I took off the rubber boot but can not move the pin, only about 1/16th inch is visible. I'm afraid to place a hex wrench on the protrusion and remove the center of the valve.
Another anomaly; when the brake pedal is depressed, fluid shoots up out of the MC, rather than when it is returned to the up position. It is bypassing somewhere.
In my nearly 40 years of driving ford trucks, starting with a new 73, I have never attacked the repositioning valve other than removing the lead to make the dash brake indicator light turn off.
Is that maze of brake lines the issue? I took off the rubber boot but can not move the pin, only about 1/16th inch is visible. I'm afraid to place a hex wrench on the protrusion and remove the center of the valve.
Last edited by pbuffing; Jul 31, 2011 at 12:53 PM. Reason: addition info
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
If you can't get fluid to the rear brakes, then it sounds like the valve is off-center; sending fluid to the fronts and blocking fluid to the rears because the differential valve "thinks" there is a leak in the rears. With all 4 bleeders closed, you should be able to slowly and firmly press the pedal down, then slowly release a few times, which is supposed to re-center the valve. If you can't get it to re-center, the valve may be stuck.
The other possibility is that fluid is not going to the rears because the replacement MC is bad. Did you bench bleed it before you installed it? This is absolutely critical.
The other possibility is that fluid is not going to the rears because the replacement MC is bad. Did you bench bleed it before you installed it? This is absolutely critical.
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From: oregone
yes, I painstakingly removed all air, it took a while. Can the center portion of the valve be removed or loosened to free up the pin?
Should the pin be protruding more than 1/16"?
the new MC reacts as did the one I replaced, other than not bleeding the system, prior to replacing the MC, but wrongly assuming the MC was the issue.
Thank you for the reply
Should the pin be protruding more than 1/16"?
the new MC reacts as did the one I replaced, other than not bleeding the system, prior to replacing the MC, but wrongly assuming the MC was the issue.
Thank you for the reply
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The pin on the front of the valve is to bypass the metering valve in the disc section of the proportioning valve when you bleed the fronts. Depending on the application, it's either pulled out or pushed in to collapse the valve and bleed the front brakes. It's completely isolated from the rear brake circuit. The length by which it protrudes from the valve body doesn't tell you anything.
As far as I know, proportioning valves are not serviceable.
As a last-ditch effort, you could try keeping both rear bleeders closed, but opening one of the front bleeders to simulate a front brake failure, then push the pedal in hopes that the pressure in the rear brake circuit and complete lack of pressure in the front brake circuit would push the valve the other direction and un-stick it. You could also disconnect the rear brake line from the MC and make sure it is outputting fluid in the first place.
As far as I know, proportioning valves are not serviceable.
As a last-ditch effort, you could try keeping both rear bleeders closed, but opening one of the front bleeders to simulate a front brake failure, then push the pedal in hopes that the pressure in the rear brake circuit and complete lack of pressure in the front brake circuit would push the valve the other direction and un-stick it. You could also disconnect the rear brake line from the MC and make sure it is outputting fluid in the first place.
Fleet Mechanic
Joined: Jan 2010
Posts: 1,287
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From: San Carlos, CA
I have had similar problems before and this is what I had to do to fix it.
I replaced the porpotioning valve. No change.
Replaced front and rear brakes. Adjusted rears as prescribed.
I replaced the master cylinder (MC) three times. The last one I purchased was from Napa auto parts and it was NEW. Not a rebuild like my previous MC from Pep Boys.
When I brought the NEW MC I bleed the MC as prescribed in the book. I was amazed how much air came out of the MC. Installed MC and bleed the system again. That was over a year ago and it has been working ever since.
The photos show the set up to bleed the MC. Use a Phillips screwdriver to push the actuator in. Note: The photo shows one of the rebuilt MC that I was trying to save. I did the same thing with the new one.
I replaced the porpotioning valve. No change.
Replaced front and rear brakes. Adjusted rears as prescribed.
I replaced the master cylinder (MC) three times. The last one I purchased was from Napa auto parts and it was NEW. Not a rebuild like my previous MC from Pep Boys.
When I brought the NEW MC I bleed the MC as prescribed in the book. I was amazed how much air came out of the MC. Installed MC and bleed the system again. That was over a year ago and it has been working ever since.
The photos show the set up to bleed the MC. Use a Phillips screwdriver to push the actuator in. Note: The photo shows one of the rebuilt MC that I was trying to save. I did the same thing with the new one.
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From: oregone
eating humble pie here... after bleeding the driver rear, and was again attempting to get some fluid to come through the passenger rear bleeder, I had my wife put extreme pressure on the pedal; I noticed a wet spot on the rear diff housing. The intermediate (bolt gone) and rear muffler (broken) brackets are as described and the tailpipe has been setting on the top of the housing hammering the brake line completely flat over a 3" area.
I'm also having problems with ex manifold leaks, was missing 2 bolts and one of the 2 that refuses to align with the block bolt hole. Likely the muffler hangers are the culprit there as well.
The the bleeder setup is nice and have learned more...
I apologize for being an blind idiot, you did kept me working on the project and not turning the truck into a cloud of smoke until I found the totally unrelated, yet root cause of the issues.
Any tricks for bending brake lines??? The flattened one has many kinks and bends.
thanks again
I'm also having problems with ex manifold leaks, was missing 2 bolts and one of the 2 that refuses to align with the block bolt hole. Likely the muffler hangers are the culprit there as well.
The the bleeder setup is nice and have learned more...
I apologize for being an blind idiot, you did kept me working on the project and not turning the truck into a cloud of smoke until I found the totally unrelated, yet root cause of the issues.
Any tricks for bending brake lines??? The flattened one has many kinks and bends.
thanks again
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Postmaster
Joined: Oct 2010
Posts: 4,656
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From: Northern and Southern Cal
I apologize for being an blind idiot, you did kept me working on the project and not turning the truck into a cloud of smoke until I found the totally unrelated, yet root cause of the issues.
Any tricks for bending brake lines??? The flattened one has many kinks and bends.
thanks again
Any tricks for bending brake lines??? The flattened one has many kinks and bends.
thanks again
As far as tube bending goes. Buy the right tools and take your time.
You can use thick wire to make patterns.
When you think you have it, check again.
Luckily your in a pretty easy area.
Have fun.
Oh, make sure you put the nipple on FIRST.
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Elder User
Joined: Jan 2004
Posts: 668
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From: NW Kans
most parts houses have premade brake lines of different lengths, with flares and fittings. just measure yours and get one thats close and replace it. You might have to put a few bends in it to get things to line up but you can do that by hand if they are not too tight of bends. just be careful not to kink the line.
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From: oregone
Im near Portland Oregon so prebent may be an option. I see all the shiny pic's of these restored trucks, nice, mine 76 is a work truck, but a good one, other than it having more NAPA parts than Ford.
When walking into the parts counter I tell them that parts for a 76 F350 NAPA are needed. We put a nice flat bed and got duals under it 4 years ago. I towed a 25' goose-neck loaded with christmas trees from just below Portland to the NAPA (CA) area for 3 years. It worked hard...
I do have a 84 F250 6.9 that has been sitting and would like to re-body, it set on a dock over the ocean most days for 12 years. I repainted it @ 3 years-old but it needed it again in another 3 years, so I gave up. I would like to shine it up again someday.
Keep up the good work.
When walking into the parts counter I tell them that parts for a 76 F350 NAPA are needed. We put a nice flat bed and got duals under it 4 years ago. I towed a 25' goose-neck loaded with christmas trees from just below Portland to the NAPA (CA) area for 3 years. It worked hard...
I do have a 84 F250 6.9 that has been sitting and would like to re-body, it set on a dock over the ocean most days for 12 years. I repainted it @ 3 years-old but it needed it again in another 3 years, so I gave up. I would like to shine it up again someday.
Keep up the good work.
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