Proportioning valve reset switch?
Burning Brakes
Joined: Feb 2004
Posts: 758
Likes: 14
From: Ville de la Baie Quebec. A winner is just a loser who tried again.
Its a brass block on the left side engine compartment, all the brake lines connect to it. Its not a P valve, its realy a just a switch, and I believe you have to create a fault in eather the front or back system and jab the brake peddle to re-set the switch. If this 
does not work,, its probably time to take it apart and clean it up,, its probably all seized up.
does not work,, its probably time to take it apart and clean it up,, its probably all seized up.
Intermediate
Joined: Sep 2005
Posts: 46
Likes: 0
Originally Posted by thevetterisbetter
How do I reset my PP valve, I read in the archives there is a switch, where is it and how do I reset it?
Thanks in advance.
Thanks in advance.
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Originally Posted by thevetterisbetter
How do I reset my PP valve, I read in the archives there is a switch, where is it and how do I reset it?
Thanks in advance.
Thanks in advance.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Originally Posted by Michel B
.... If this does not work,, its probably time to take it apart and clean it up,, its probably all seized up.
does not work,, its probably time to take it apart and clean it up,, its probably all seized up.
All of the Vette brake jobs that I have done where the switch went off center, and the (C2/C3) Vette was 5 years old or older, the switch was completely plugged up with sludge.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
The switch varies in design depending on year.
Typically, the actual switch has to be removed first because it hangs up the internals.... similar to the fuel pump rod hanging up the camshaft. Be careful of any gaskets/seals. There may be a nylon gasket on the switch part, or it may be NPT. It's been a while, but I think I had to pull the brass inverted flare seat on some of them to allow the internal pieces to come out. To avoid damaging the seat, I tap the center hole with the smallest tap that fits well, and I use a machine screw to pull the seat out. This way it can be re-installed.
The internals vary, so you have to judge what needs TLC bsed on design. Some have o-rings, some do not.
I would have to take a look at the pics I have on file to be sure.... writing this from a burned out musicians brain... so take it with a grain of salt.
Typically, the actual switch has to be removed first because it hangs up the internals.... similar to the fuel pump rod hanging up the camshaft. Be careful of any gaskets/seals. There may be a nylon gasket on the switch part, or it may be NPT. It's been a while, but I think I had to pull the brass inverted flare seat on some of them to allow the internal pieces to come out. To avoid damaging the seat, I tap the center hole with the smallest tap that fits well, and I use a machine screw to pull the seat out. This way it can be re-installed.
The internals vary, so you have to judge what needs TLC bsed on design. Some have o-rings, some do not.
I would have to take a look at the pics I have on file to be sure.... writing this from a burned out musicians brain... so take it with a grain of salt.
Thread Starter
Pro
Joined: Jan 2004
Posts: 522
Likes: 0
From: Grayslake IL
Well the light went out after stomping on it, but now I cannot bleed my back brakes, as if the switch is locking out the back brakes and having only the front brakes open. Should I have the engine running when I stomp on it to reset it? I am using a motive power bleeder and still get nothing coming out of the back bleeder screws.
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Advanced
Joined: Apr 2005
Posts: 96
Likes: 0
From: Ogden Iowa
Not to hijack the thread, but can pp years interchange? I think the one in my 73 needs replaced, but GM doesn't have them, and they said 78+ would interchange. Would lines be the same? And arent 78+ a true prop valve?
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Originally Posted by savage118
Not to hijack the thread, but can pp years interchange? I think the one in my 73 needs replaced, but GM doesn't have them, and they said 78+ would interchange. Would lines be the same? And arent 78+ a true prop valve?
Advanced
Joined: Apr 2005
Posts: 96
Likes: 0
From: Ogden Iowa
Originally Posted by Duke94
If your valve is mounted vertical on a bracket off the frame under the M/C, then it is a differential (switch) valve only. If it's mounted horizontally on the frame with two bolts then it has a proportioning valve. They are not interchangable due to the brake line differences. The proportioning valve was added to meet the government (DOT)stopping distance requirements in the early 70's.
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Originally Posted by savage118
I figured the parts guy did not know what he was talking about. Thanks. But what happens if Iyou FUBAR the original one trying to clean it? Out of production @ GM. Funny for such an important part.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
I have pictures of a 70 valve disassembled & cleaned if you're interested. 2 pistons with an o-ring on each, and the switch also has 2 o-rings on it.
I also have an 80 but could not find the pics... I think I migrated them to a ZIP drive to free up disk space.
If you need those, I can try to find them.
I also have an 80 but could not find the pics... I think I migrated them to a ZIP drive to free up disk space.
If you need those, I can try to find them.
Team Owner
Joined: Jul 2004
Posts: 40,352
Likes: 787
From: Redondo Beach, California
Originally Posted by Duke94
Your only choice then is to buy a used one and rebuild it. Only has 2 o'rings on a piston inside, not to complicated.
My original 68 block was a rectangular block of cast iron. The new repro version is manufactured from a block of steel stock.
I saw an original used 1968 distribution block for sale for $200!
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Originally Posted by thevetterisbetter
Well the light went out after stomping on it, but now I cannot bleed my back brakes, as if the switch is locking out the back brakes and having only the front brakes open. Should I have the engine running when I stomp on it to reset it? I am using a motive power bleeder and still get nothing coming out of the back bleeder screws.
On the ones I have worked on, the switch/pp valve was completely plugged up with sludge. Because of the sludge, when it slipped to one side, it was usually impossible to re-center it without blowing compressed air backwards through the line. I would try the pedal method first. When that failed, compressed air.
For example, if the rear circuit had leaked & was now blocked by the switch, I would blow air backwards through a rear line.... LOW pressure, using a rubber air gun tip. I would loosen the M/C cover and put a large rag on top of the M/C as well. Because the other (front in this example) circuit was still closed, the switch would have a difficult time of going back.... but it worked sometimes. When it didn't, I pulled the switch & disassembled it. This is risky because of parts availability, so I tried to avoid it if possible.
Once it centers, I bleed BOTH a front and a rear at the same time to avoid letting the switch go off center again.
If you're not getting any fluid out of one circuit, either the switch is still blocking, or you have internally collapsed rubber brake hoses.
Burning Brakes
Joined: Sep 2009
Posts: 1,124
Likes: 140
From: Western New York
I know you said you put on some new rubber lines, but it could be one of the new ones and not the pp valve. To check without replacing hoses, just loosen the upstream end of the hose from the hard line to see if the pressure releases. If it does, then have someone put pressure on the brake pedal and see if you get fluid out of the loose fitting. If you do, then the fluid is getting past the pp valve and your problem is the rubber line.
Duane
Duane
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
If your valve is mounted vertical on a bracket off the frame under the M/C, then it is a differential (switch) valve only. If it's mounted horizontally on the frame with two bolts then it has a proportioning valve. They are not interchangable due to the brake line differences. The proportioning valve was added to meet the government (DOT)stopping distance requirements in the early 70's.
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
