Proportioning Valve - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

old trucks again · 01-02-2005, 12:39 AM

i had a very simiar problem with a 67 c10 i recently purchased (with poorly fuctioning brakes),after much frustration,i realized the guy before me,had the lines from the porportion valve,to the front and rear,backwords.you never can take it for granite.
marvin.

avejoe · 01-02-2005, 01:03 AM

I thought about this too. According to the GMC service manual the lines are to the prop. valve correctly for a 1/2 ton.

Thanks!

franko72 · 01-02-2005, 01:54 PM

I did the same thing and found that the prop valve was bad.

avejoe · 01-02-2005, 04:52 PM

Blew air throught the front lines with no problem today. All signs point at the proportioning valve.

LONGHAIR · 01-02-2005, 06:22 PM

Is the "Brake" light on? (on the dash) This is probably from having the rear brakes bled and having a pressure imbalance.
It sounds funny, but the back brakes are likely causing the problem.
The first thing to do is make sure that every bleeder will open and that they are not clogged.
Next, open the rear bleeders (with the fronts closed) and let them flow a bit. Press the pedal to the floor and see if you can get it the proportioning valve "pop" back......the light will go off.
Then open the front bleeders and allow everything to gravity bleed for a while (don't let it run dry)
After they all flow freely tighten the bleeders. You should have a fairly good pedal at that point.
Start bleeding from the right rear and work yourself toward the left front (last)......have the key on and be aware of the brake light. Don't let the pedal get down far enough to pop the switch.

We really need something about this on the FAQ page, it comes up a lot.

avejoe · 01-02-2005, 07:36 PM

Is the brake light controlled only by the position of the prop valve or only pressure?

dwaite72lnghrn · 01-02-2005, 09:35 PM

Leave the small rubber boot on the front of the proprtioning valve and use a piece of angle iron and a vise grip, Push in on the boot with the angle iron then clamp tight against the sides with the vise grips, Then bleed the brakes front and back. This has worked for me in the past.

LONGHAIR · 01-02-2005, 10:42 PM

The light is controlled by the valve.....and the valve is controlled by the lack of pressure on one side or the other.

avejoe · 01-03-2005, 12:55 AM

I used a c-clamp to hold the button in but I could not pull any fluid through the front using a vac. I pulled the boot off prior to using the c-clamp. I will put the boot on and c-clamp it tomorrow and try to bleed it using the old fashioned way with a helper.

I am pretty sure now I have never had front brakes in this truck. No wonder the pads look so good.

I feel like I am zeroing in on it.

My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me.

RICHARD MORGAN · 01-08-2005, 07:06 PM

Im having the same situation. Id have to just about stand on the brakes to stop. My master cylinder was leaking a little bit so i replaced it and bled the brakes, but the brakes still werent hard. The rubber brake lines looked kind of old and weathered so i relaced them with stainless ,but the brakes still werent hard. I then replaced all the hard brake lines with a prebent stainless kit. So all i have left is the booster and the proportional valve. The booster was $70 and im putting it on this week. If that dont do it i guess ill be buying a new proportional valve.

Richard

avejoe · 01-09-2005, 12:43 AM

I put a new (used) prop valve on today. No change. I can get the truck to stop but I can't lock it up.

Is your prop valve off-setting?

I'm really getting annoyed. Have you changed the front calipers?

What year is your truck?

ssfirefighter · 04-27-2008, 10:52 PM

I have been fighting the same problem for some time now as well. I have a new master cylinder, new proportioning valve, new front brake hoses and the thing bleeds good. I didn't depress the ''button'' on the front of the proportioning valve when I did it though. The thing will stop, but no matter how hard I press it will not lock up. Just at idle it won't even dip the front end. I am thinking new wheel cylinders and calipers? Any more help?

chipflyer · 04-27-2008, 11:40 PM

I bought a brand new master cylinder at Advance Auto and went through the same stuff you are going through, no front brakes and everything else replaced. I finally suspected the master cylinder was bad (from advice on here) and had them order me another one and a completely different (wrong) master cylinder showed up in a correctly numbered box. They apologized and ordered me another new one, the wrong part came in again in the correct box. Then he ordered 3 of them that were at their warehouse and guess what, 3 different master cylinders! He was embarrassed, apologized, and refunded my money. I went to NAPA and picked up a re manufactured Master Cylinder and I had no trouble bleeding the brakes and had a great pedal in about 10 minutes.
I really don't think you have a problem with your prop valve, there is not much in there to go bad and as Longhair stated, it just moves from the center to one end or the other when there is a leak in the system and if you can make the light go out it is fine. Yours is doing exactly what mine did before I finally got a good master cylinder. Either go get another or borrow a know good one from someone and do some testing.
center
Jeff

LONGHAIR · 04-28-2008, 01:15 AM

ssfirefighter,
You really should have started your own thread, instead of hi-jacking one that is over 3yrs old.
Some more info might help too. You said that you have a new M/C but how about the booster? Did you flush the lines? Good clean fluid? Is it bleeding well to all 4 corners? Pedal freeplay? etc....

ssfirefighter · 04-28-2008, 06:36 AM

Sorry. I posted to see what he figured out, and thought the last post was in 01-08, but it was 01-08-05 sorry.

Anyway, the booster seems to be fine. I have a vacuum reserve on it and it holds good vac. I have bled a good two 32 oz bottles of fluid through it and it bleeds clean. The pedal feels spongy though and it just doesn't stop like it should. If I really stand on it, it just comes to a nice smooth stop and won't stop hard at all.

bigblockorange · 04-28-2008, 11:57 AM

I took the easy way out! My local garage bled my brakes with a power bleeder for $20 no mess no hassle

jhow66 · 04-28-2008, 05:45 PM

Quote:

Originally Posted by ssfirefighter

Sorry. I posted to see what he figured out, and thought the last post was in 01-08, but it was 01-08-05 sorry.

Anyway, the booster seems to be fine. I have a vacuum reserve on it and it holds good vac. I have bled a good two 32 oz bottles of fluid through it and it bleeds clean. The pedal feels spongy though and it just doesn't stop like it should. If I really stand on it, it just comes to a nice smooth stop and won't stop hard at all.

Adjust your booster to MC rod longer--not enough travel to use all of MC. (my guess) (be careful to not get it to long as it will not then retract enough)

jayharrell · 04-28-2008, 06:02 PM

http://www.classicperform.com/TechBo...tm#testbooster

Its basic stuff, but this help me out with the problem. Mine turned out to be a bad right rear cylinder. Also with mine being a long bed, it took a few days of driving around to shake all the air loose. My brakes wern't the best after the first bleed, but i did it again a week later, and now they are almost damn perfect.

Also check the vacume on the motor. Make sure you are getting the right amount to the booster.

01-02-2005, 01:03 AM	#27
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	I thought about this too. According to the GMC service manual the lines are to the prop. valve correctly for a 1/2 ton. Thanks! __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage

01-02-2005, 01:54 PM	#28
franko72 Franko72 Join Date: May 2004 Location: Cincinnati,Ohio Posts: 471	I did the same thing and found that the prop valve was bad. __________________ 1972 C20 cheyenne Super 402 BB/400 turbo LWB A/C Tilt, Cruise Control, Saddle tanks, Tach My Home Page Better to burn out than it is to rust

01-02-2005, 04:52 PM	#29
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	Blew air throught the front lines with no problem today. All signs point at the proportioning valve. __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage

01-02-2005, 07:36 PM	#31
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	Is the brake light controlled only by the position of the prop valve or only pressure? __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage Last edited by avejoe; 01-02-2005 at 09:42 PM.

01-02-2005, 09:35 PM	#32
dwaite72lnghrn Registered User Join Date: Jun 2002 Location: central pa Posts: 1,525	Leave the small rubber boot on the front of the proprtioning valve and use a piece of angle iron and a vise grip, Push in on the boot with the angle iron then clamp tight against the sides with the vise grips, Then bleed the brakes front and back. This has worked for me in the past. __________________ 72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne

01-02-2005, 12:39 AM	#26
old trucks again Registered User Join Date: Dec 2004 Location: bolinas,ca. Posts: 9	i had a very simiar problem with a 67 c10 i recently purchased (with poorly fuctioning brakes),after much frustration,i realized the guy before me,had the lines from the porportion valve,to the front and rear,backwords.you never can take it for granite. marvin.

01-02-2005, 06:22 PM	#30
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Is the "Brake" light on? (on the dash) This is probably from having the rear brakes bled and having a pressure imbalance. It sounds funny, but the back brakes are likely causing the problem. The first thing to do is make sure that every bleeder will open and that they are not clogged. Next, open the rear bleeders (with the fronts closed) and let them flow a bit. Press the pedal to the floor and see if you can get it the proportioning valve "pop" back......the light will go off. Then open the front bleeders and allow everything to gravity bleed for a while (don't let it run dry) After they all flow freely tighten the bleeders. You should have a fairly good pedal at that point. Start bleeding from the right rear and work yourself toward the left front (last)......have the key on and be aware of the brake light. Don't let the pedal get down far enough to pop the switch. We really need something about this on the FAQ page, it comes up a lot.

01-02-2005, 10:42 PM	#33
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	The light is controlled by the valve.....and the valve is controlled by the lack of pressure on one side or the other.

01-03-2005, 12:55 AM	#34
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	I used a c-clamp to hold the button in but I could not pull any fluid through the front using a vac. I pulled the boot off prior to using the c-clamp. I will put the boot on and c-clamp it tomorrow and try to bleed it using the old fashioned way with a helper. I am pretty sure now I have never had front brakes in this truck. No wonder the pads look so good. I feel like I am zeroing in on it. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. My truck is not smarter than me. __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage

01-08-2005, 07:06 PM	#35
RICHARD MORGAN Registered User Join Date: Jan 2004 Location: HERNDON VA Posts: 216	Im having the same situation. Id have to just about stand on the brakes to stop. My master cylinder was leaking a little bit so i replaced it and bled the brakes, but the brakes still werent hard. The rubber brake lines looked kind of old and weathered so i relaced them with stainless ,but the brakes still werent hard. I then replaced all the hard brake lines with a prebent stainless kit. So all i have left is the booster and the proportional valve. The booster was $70 and im putting it on this week. If that dont do it i guess ill be buying a new proportional valve. Richard

01-09-2005, 12:43 AM	#36
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	I put a new (used) prop valve on today. No change. I can get the truck to stop but I can't lock it up. Is your prop valve off-setting? I'm really getting annoyed. Have you changed the front calipers? What year is your truck? __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage

04-27-2008, 10:52 PM	#37
ssfirefighter Registered User Join Date: Nov 2007 Location: DFW, TX Posts: 32	Re: Proportioning Valve I have been fighting the same problem for some time now as well. I have a new master cylinder, new proportioning valve, new front brake hoses and the thing bleeds good. I didn't depress the ''button'' on the front of the proportioning valve when I did it though. The thing will stop, but no matter how hard I press it will not lock up. Just at idle it won't even dip the front end. I am thinking new wheel cylinders and calipers? Any more help?

04-27-2008, 11:40 PM	#38
chipflyer Registered User Join Date: May 2004 Location: Topeka, Ks Posts: 2,293	Re: Proportioning Valve I bought a brand new master cylinder at Advance Auto and went through the same stuff you are going through, no front brakes and everything else replaced. I finally suspected the master cylinder was bad (from advice on here) and had them order me another one and a completely different (wrong) master cylinder showed up in a correctly numbered box. They apologized and ordered me another new one, the wrong part came in again in the correct box. Then he ordered 3 of them that were at their warehouse and guess what, 3 different master cylinders! He was embarrassed, apologized, and refunded my money. I went to NAPA and picked up a re manufactured Master Cylinder and I had no trouble bleeding the brakes and had a great pedal in about 10 minutes. I really don't think you have a problem with your prop valve, there is not much in there to go bad and as Longhair stated, it just moves from the center to one end or the other when there is a leak in the system and if you can make the light go out it is fine. Yours is doing exactly what mine did before I finally got a good master cylinder. Either go get another or borrow a know good one from someone and do some testing. center Jeff __________________ I'm not a pessimist, I'm just optimistic that bad things are going to happen. 1971 Cheyenne Super K10 - tilt, cruise, air, am/fm, tow hooks, factory buckets! 1986 Jeep J10 pickup, - 5.3L Vortec with 4L60e and NP241. Last edited by chipflyer; 04-28-2008 at 02:02 AM.

04-28-2008, 01:15 AM	#39
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Proportioning Valve ssfirefighter, You really should have started your own thread, instead of hi-jacking one that is over 3yrs old. Some more info might help too. You said that you have a new M/C but how about the booster? Did you flush the lines? Good clean fluid? Is it bleeding well to all 4 corners? Pedal freeplay? etc....

04-28-2008, 06:36 AM	#40
ssfirefighter Registered User Join Date: Nov 2007 Location: DFW, TX Posts: 32	Re: Proportioning Valve Sorry. I posted to see what he figured out, and thought the last post was in 01-08, but it was 01-08-05 sorry. Anyway, the booster seems to be fine. I have a vacuum reserve on it and it holds good vac. I have bled a good two 32 oz bottles of fluid through it and it bleeds clean. The pedal feels spongy though and it just doesn't stop like it should. If I really stand on it, it just comes to a nice smooth stop and won't stop hard at all. Last edited by ssfirefighter; 04-28-2008 at 06:37 AM.



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04-28-2008, 11:57 AM	#41
bigblockorange Senior Member Join Date: Jan 2007 Location: central pa Posts: 428	Re: Proportioning Valve I took the easy way out! My local garage bled my brakes with a power bleeder for $20 no mess no hassle Attached Images __________________ I guess you could say I’m not really lazy I’m just real good at doing nothing!!!!

04-28-2008, 06:02 PM	#43
jayharrell Gettin By on Gettin By Join Date: Jan 2008 Location: Cedar Creek, Tx Posts: 1,033	Re: Proportioning Valve http://www.classicperform.com/TechBo...tm#testbooster Its basic stuff, but this help me out with the problem. Mine turned out to be a bad right rear cylinder. Also with mine being a long bed, it took a few days of driving around to shake all the air loose. My brakes wern't the best after the first bleed, but i did it again a week later, and now they are almost damn perfect. Also check the vacume on the motor. Make sure you are getting the right amount to the booster. __________________ 69 CST10 LWB 455 Buick 00 S10 2.2 Vin5 76 GL1000 Naked 1bl VW carb "Adios to all the concrete; Gonna get me some dirt road back streets"

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