Wire going to prop valve

[AnotherWs6]

Sorry if this is in the wrong spot. What does the wire going to the proportioning valve do? I saw a post talking about needing to do something with it while bleeding the brakes. I won't be offended by any "noob" comments. Thanks.

Oh, does my setup look correct for 4 wheel power drums?

[Already Gone]

I am pretty sure the wire is there and connected to the brake light light on your. dash So if something happens to your brakes, like a brake line breaks and you loose brake fluid the brake light on your dash will light up telling you there is a problem with your brakes.

[old Chevy guy]

That wire goes to the brake warning light in the instrument cluster. It would come on if you lose some or all of your brakes or just problem indicater in general. In some cases I've read where you need to thread that switch out to bleed brakes on certain models . I don't know all the details but somebody will most likely chime in or you could do a thread seach on bleeding brakes and I'm sure a ton of info on the subject will come up. Your pictures are not coming through for me so I can't answer your other questions.

[AnotherWs6]

ANother stupid question but I'm 50 miles from it so..... what is underneath the wire cap?

[geezer#99]

It's for your brake 'failure' light.

[AnotherWs6]

Then no special instructions for bleeding the brakes....

[FirstOwner69]

Your setup looks correct for drum/drum brakes.

Mine bleed just fine with everything attached.

[mike16]

Originally Posted by AnotherWs6

Then no special instructions for bleeding the brakes....

there is actually, and not having a service manual can stump the best of us. under the wire cap is a switch. it normally is open but when there is a break failure and a loss ofr fluid/pressure on one part of the system , a floating piston inside the prop valve. when one side of the system looses pressure. the high pressure side of the system still working, pushes the floating piston to the low sid, the piston being made of a conductive alloy, will close the electrical cuircut and electricity will then be able to complete the cuircut, lighting up the brake lite.

the special procedure is to unscrew the switch in the prop valve and recenter the piston if it has moved off center in either direction. the other special procedure is to unscrew that same switch and place a special tool in side the threadded hole to maintain the piston in the center position.

if you over look these procedures, bleading one or the other side of the system becomes impossible

this has stumped some of the best mechanics among us.

long winded as my response is. get a service manual. it shows diagrams, photo's and explains the procedure.

[AnotherWs6]

Well check out post #3 of this thread. I have wonky brake problems BTW.

http://67-72chevytrucks.com/vboard/s...d.php?t=707428

[old Chevy guy]

The switch under that wire has a pin that is part of a micro switch that turns the light on when there's a problem the prop valve slids one way or the other and trips that switch. My brakes bled and bled but still acted funny and the light wouldn't go off. I threaded that switch out and it was kind of stuck but came out with kind of a pop then the light went off and the problem went away. Not sure what happened but it has something to do with that valve getting back to center. My truck is front disc so we may be talking apples and oranges. That setup does look correct ,I can see your pics now.

[AnotherWs6]

I just bought a full disc brake kit, came this week. I got really frustrated with my brakes. Now I'm second guessing myself. I never did anything with the prop valve even though I suspected something might be wrong there. Or the wrong one in general. It seems there is a decent amount to learn about this little valve.

[AnotherWs6]

Not long winded - probably just took a couple minutes to type.

[FirstOwner69]

Let's take a step back. The OP actually has the correct distribution block for his drum/drum setup. I think most of the comments regarding bleeding apply to proportioning valves not distribution blocks. Please correct me if I'm wrong.

[70STOVEBOLT]

Originally Posted by FirstOwner69

Let's take a step back. The OP actually has the correct distribution block for his drum/drum setup. I think most of the comments regarding bleeding apply to proportioning valves not distribution blocks. Please correct me if I'm wrong.

BINGO! The 4 wheel drum system does not use a proportioning valve, it uses a distribution block.

[AnotherWs6]

^^^^^^Uh-oh. Are you saying I have one and not the other? I'd say what you're calling a distribution block and what I'm calling a prop valve are the same thing, no?

[AnotherWs6]

But they do the same thing, no? Dictate how much pressure gets to each axle, right?

[70STOVEBOLT]

Read the first page of this link, it describes both pieces: http://www.getdiscbrakes.com/knowled...Configurations

[AnotherWs6]

Originally Posted by 70STOVEBOLT

Read the first page of this link, it describes both pieces: http://www.getdiscbrakes.com/knowled...Configurations

Wow, things are a lot more complicated than I thought.

[mike16]

Originally Posted by AnotherWs6

Wow, things are a lot more complicated than I thought.

no not really. The info on the perportioning valve comes from my 72 service manual. the info on the distributor block comes from the 68 manual.

I knew it was mis called but the picture and the refference to drum brakes were a clue. there are no refferences to perportioning valves in 4 wheel drum brake equiped trucks in either service manual.

Those service manuals ......

I have a kent moore tool that holds the piston on center. If i can find it I will post a picture. Typically the service manual describes services performed on trucks at the dealership under warrenty. now that these trucks are 45-50 years ols different problems, different symptoms and different troubleshooting skills are required. My service manual states that the warning lite can be tested by cracking open a bleeder valve and hitting the brakes. it also states that closing the bleader valve and hitting the brakes will re center it. but when these trucks are as old as they are rust and dirt can get into the system and cause the piston to stick and if you dont know that when you bleed the system.... it can drive you crazy. trying to troubleshoot the sytem using the service manual elclusively. Its happened enough to me that I know to go in to the perportioning valve/ distributor block through the switch openining with a small screw driver like the ones used to repair screws in glasses. and physically move and recenter the piston.

I have found that soaking and flushing the prop/distribution block in alcocol can clean them out pretty good, but not always. no service manual spells that out but keep it in mind when you rebuild your brake system. How many of us remove and clean that when we do a major brake overhual? pumping fresh fluid through helps but its solvent effect on dirt and rust can loosen dirt and rust over time and send it through the system. like using detergent oil in an engine that has never used detergent oil befor. it can cause a few unanticipated problems. flushing it once may be good but doing it several times over a period of weeks is a better ides.

Any way... that perprtioning valve... the on on your drum brake truck....

WS6, good web site on those "valves" but notice that perportioning valves are commonly found on disc/drum vehicles. but they can be also found on drum drum trucks. Its just a name to destinguish it from another nomanclature. like suzie is different from annie... e

[mike16]

what does the service manual call it. Suzie? Annie? regardless. the balance of the point i was making was how it should be serviced. have I mentioned the importance of the service manual?

[FirstOwner69]

Originally Posted by mike16

what does the service manual call it. Suzie? Annie? regardless. the balance of the point i was making was how it should be serviced. have I mentioned the importance of the service manual?

Agree 100%. Use a service manual.
The manual for 72s says "The combination valve, located near the master cylinder, must be held in the open position while bleeding". It then goes on to explain how to accomplish that. Interesting that they call it a combination valve. The 69 manual makes no such statement because there is no valve contained within the distribution block.

[WorkinLonghorn]

Mike16 wrote;

the special procedure is to unscrew the switch in the prop valve and recenter the piston if it has moved off center in either direction. the other special procedure is to unscrew that same switch and place a special tool in side the threadded hole to maintain the piston in the center position.

if you over look these procedures, bleading one or the other side of the system becomes impossible

this has stumped some of the best mechanics among us.

long winded as my response is. get a service manual. it shows diagrams, photo's and explains the procedure.

Mike, this is interesting. Which manual has the pictures and diagrams?
The "Chevrolet Truck Service Manual" for 1969 just says to bleed them without any concern for the distribution block.

In the section for testing the warning light it says to open a rear bleeder and apply the brakes and watch for the light to come on, but it does not mention and need to reset the switch.

Since mine has never worked (two trucks, 27 years) I would not know if this is needed or not but I intend to correct this and would like to see these special instructions, Thanks, WL

[FirstOwner69]

Originally Posted by WorkinLonghorn

Mike16 wrote;

Mike, this is interesting. Which manual has the pictures and diagrams?
The "Chevrolet Truck Service Manual" for 1969 just says to bleed them without any concern for the distribution block.

In the section for testing the warning light it says to open a rear bleeder and apply the brakes and watch for the light to come on, but it does not mention and need to reset the switch.

Since mine has never worked (two trucks, 27 years) I would not know if this is needed or not but I intend to correct this and would like to see these special instructions, Thanks, WL

There is no valve in the distribution block (which the OP mistakenly referred to as a prop valve in this thread...a common mistake). This is from the link in 70STOVEBOLT's post above:
"Distribution Block- This block distributes the fluid to different lines in the system and includes a failure warning switch that turns on a warning light in the event of a half system failure. It does not proportion or meter the brake fluid coming from the master cylinder."

Apparently, no special procedure is required with a distribution block.

The link also described the operation of a proportioning valve:
"Proportioning Valve- A proportioning valve restricts the amount of pressure to the rear of a brake system under heavier braking conditions to prevent the rear brakes from locking up too soon. Proportioning valves were usually only found on vehicles with front disc brakes."

[mike16]

he asked what the perportioning valve wire does, and I responded to another post about servicing it properly. I recomended referrencing a service manual. my bad, sorry

[old Chevy guy]

Originally Posted by AnotherWs6

Sorry if this is in the wrong spot. What does the wire going to the proportioning valve do? I saw a post talking about needing to do something with it while bleeding the brakes. I won't be offended by any "noob" comments. Thanks.

Oh, does my setup look correct for 4 wheel power drums?

And another thing is if you changed to disk this is not the right master cylinder for a disk / drum setup. Correct me if I'm wrong, but wont you also need a ''prop'' valve ( 71-72) to correctly run the disk system? Seems like the forest has been lost in the trees here. we have lots of good answers here but not the right question I think.