Proportioning Valve

[avejoe]

I installed a new master cylinder (sp?) today and I can't get my brakes to firm up. I bench bled the MC and bled the rear drums. I can't get the fronts (discs) to bleed. One side won't bleed any juice past the first set of stokes. I can't get the bleed valve open on the other side.

Do I need to bleed the proportion valve? What is the rubber booted button on the front of the prop. valve for?

Thanks!

[JayDubBlazer]

I would like to know what that nub is on the bottom for as well.

[gonebad2]

Take the bleeders out of the cailpers. Look closely and see if the holes are plugged up with rust, dirt or grease. Try cleaning them out with a small sharp object then blowing compressed air through them. Or, hit the auto parts store on Sunday and get some replacements. I'm not fond of GM's design with the bleeders pointing straight up. Originally, they installed rubber caps on them to keep the junk out but they didn't last long. I have never had to bleed a prop valve. On my last buildup, I installed a complete new braking system ( new booster, master cyl, prop valve, hard lines, soft lines, calipers, wheel cylinders) and it bled out just fine. Good Luck!!

[jhow66]

Is your brake warning light on?

[avejoe]

The brake light was on then I bled the system a little more and it went out but the brakes still barely stop the truck. I have a de facto ABS system.

Still no answer on the button on the front to the proportioning valve, eh? Can proportioning valves go bad?

I did have to manually clear out one of the bleeder valves but the others are clear, including the one that won't bleed well. I will replace the bleeder valves all the way around.

Keep the answers coming and have a great Christmas!!!!!!

Thanks

[67ChevyRedneck]

You have ABS???? On a 67to72??? That could be your problem....aren't they electrically controlled??? Sorry, but I don't know much of anything about ABS.... Also, check your calipers, are they old and rusty? They can freeze up and that would cause them to not work and not bleed. To check, take the calipers off the truck and take out/loosen the bleeder valves. You SHOULD be able to push them closed with your hand. If not, try a bench vice to slowly "unlock" them by closing it. If they don't free up you probably need new ones. I redid my suspension last year with ALL new parts, I think they calipers were only $25 a piece brand new. JMOH, good luck!!!

[avejoe]

ABS as in no matter what I can't lock the brakes up!

[4x4Poet]

Whenever I'm afforded the opportunity, I pimp Russell Performance's speed bleeders. One man bleeding. They have a spring loaded ball that prevents air from going back up the bleeder. They also have a sealant coating the threads for leak free protection. I work on my trucks alone, most of the time, so I cherish those little buggers. No more having to find a helping hand (or pedal foot).

You've already bought the master. If the budget allows, pick up new/reman calipers and install speed bleeders, which are available thru Summit and Jegs among other sources. Note the speed bleeder bag Russell makes shown at the bottom of the link. Less mess with inverted bleeders. I found it in Jegs, I think. Maybe Summit.

[Sweet72]

Remove that rubber cap on the proportioning valve and depress and hold the small pin while bleeding. GM calls for a special tool to hold it in, but you can improvise with a c-clamp or rig something up. You must do this or you cannot fully bleed the system. Install new bleeder screws. Tap on the calipers with a mallet or wood block while bleeding to evacuate all air bubbles.

[JayDubBlazer]

does somebody have a picture of a proportioning valve and an illustrated picture of a master cylinder showing what all the lines do.

[avejoe]

Ok, now I'm pissed.

I put in new bleeders. Re-bench bled the MC. Bled the sh_t out of the brakes and I still can't get much fluid out of the fronts. The pedal is still real soft.

I removed the boot on the prop valve. There is a small hole that appears to be a small check valve. Is that what I hold in? How could you ever get a c-clamp to hold it as it is so small?

How do you know if a prop valve is bad?

So much for my Sunday.

Thanks!

[gonebad2]

How about the holes on the calipers under the bleeders? There could possibly be some corrosion built up in there. Just a thought.... Remove the bleeders and push a sharp object like a scribe in there. Have a helper lightly press the brake pedal. See how much fluid will come out with the bleeders removed.

[4x4Poet]

You might disconnect one of the front brake hoses from a caliper to check for fluid flow from the master and proportioning valve.

With good fluid flow out the front hose-ends, I'd suspect the calipers before the proportioning valve. The calipers endure both rotor/pad heat and direct contact with road grime. The proportioning valve endures little or no heat and is protected from road grime by the engine/frame/skirts. If you can dinker with the p-valve you have to fix the front brakes, then great. If you think you need a new p-valve without discovering an overt cause, then I'd install new calipers before replacing the p-valve. Just my 2¢.

[avejoe]

Yeah, I'm thinking I should replace the calipers. The rotors seem to be in real good shape with little scoring. It appears to be a real bi*ch to pull the rotors on a 4x4 to have them turned. Would it be horrible to replace the calipers w/o turning the rotors?

Also, when I bench bled the MC I was getting better flow from the rear bowl. No air in either, but less flow in the front. Is this normal?

With properly functioning brakes I should be able to lock the wheels up right?

Thanks!

[Sweet72]

avejoe,
There should be a small diameter pin on the end of the prop valve. It will depress only a small amount (about 1/32 in.). If yours has a hole where the pin should be somethings wrong. It's been a long time since I've bled brakes on my truck (5 yrs since I disassembled it for a frame off) so I don't remember what I used to hold that pin in. Yes, you should be able to lock 'em up with no problem.

[avejoe]

The rubber boot protects a button about 3/8" in diameter. In the center of the button there is a round indent that you can fit a small phillips head screw driver in and depress it a small amount. Do I need to indent the whole 3/8 inch button or the indent? I tried to press the whole button but nothing moved.

I've never done this before so I have nothing to compare.

The Chilton's manual says nothing.

[4x4Poet]

Originally Posted by avejoe

...The rotors seem to be in real good shape with little scoring. It appears to be a real bi*ch to pull the rotors on a 4x4 to have them turned. Would it be horrible to replace the calipers w/o turning the rotors?

Considering how inexpensive rotor turning is, yes.

Originally Posted by avejoe

Also, when I bench bled the MC I was getting better flow from the rear bowl. No air in either, but less flow in the front. Is this normal?...

Tough to say from your description. The main thing is achieving no air bubble fluid flow. When bench bleeding my TravelAll's master last Summer, I also noticed less flow into the front reservoir. Either this has to do with the light pressure bench bleeding entails, or some engineering factor favors the rear system with the dual master design. Just conjecture.

[Tx Firefighter]

Originally Posted by 4x4Poet

Considering how inexpensive rotor turning is, yes.

I disagree with that. If the rotors are in proper condition without grooves or warping, I'd leave them on the truck and just deglaze the surface with an abrasive.

There's no reason to remove mass from the rotors by machining them unnecessarily. Plus, he said they are hard to get off (4x4), so why do it?

I do agree that he needs to disconnect the banjo bolt and see how good the fluid passes through the front rubber hoses. He wouldn't have the first truck with a set of internally swollen front hoses that didn't want to pass fluid. I've been fooled by that one years ago and learned my lesson well.

[Vince M]

I have seen brand new and/or remanufactured master cylinders be bad right out of the box. Don't assume it is good. Start at the master cylinder loosen the line fittings and see if you get any fluid out. Work your way down to the caliper one fitting at a time. Anything could have gotten into the brakeline once it is opened up. My bet is there is something stuck in the line somewhere. When I open my bleeders I get liquid out just from the gravity of the master cylinder being above the calipers. Don't loose hope. I always look at it that my truck is not smarter than me.

[avejoe]

Thanks for all the info. I will be back at it this afternoon.

Sorry to say that at the moment my truck is smarter than me.

[Sweet72]

avejoe,
I think your prop. valve is fubar. I just looked at mine and in the center of that 3/8 "tit" is the 1/16 pin protruding about 1/32. Check the links below, I believe you should get a new valve. I'm with Texas Firefighter on the front brake hoses.
http://auto.howstuffworks.com/master-brake2.htm
http://www.inlinetube.com/articles/O...Proportion.htm

[avejoe]

I continued my brake woes in a new thread:

http://67-72chevytrucks.com/vboard/s....php3?t=132831

I sure would appreciate some comparison help on my master cyl questions.

Thanks!

[franko72]

if your proportioning valve is corroded and stuck in any certain position, you may not get any fluid to one or more of the wheels.Mine went out in my jeep a while back.I changed all the pads and shoes and noticed that it pulled when the brakes were applied.found that the right side caliber wasnt getting any fluid no matter what I did.removed and disassebled the prop valve .It was gummed up pretty bad and sticking.bought a new one and bled all the brakes.everything works fine now.

[Huck]

I would remove the bleeder from the caliper that is not bleeding and push on the brake. You should get plenty of brake fluid coming out. If not, disconnect the brake line at the cliper or where the rubber line connects to the solid line at the frame. This way you are tracing the problem from the obvious weak bleeder backwards. You can go either way but ------bottom line, you can't expect solid braking if you are not getting a stong flow from a caliper bleeder when you push on the brake.

[avejoe]

Tomorrow I'm going to crack the driver front bleeder and disconnect the line under the proportioning valve and blow air through with my compressor. If the air flows then I know the proportioning valve needs replacement.