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#26 |
Registered User
Join Date: Dec 2004
Location: bolinas,ca.
Posts: 9
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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. |
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#27 |
Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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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!
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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 |
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#28 |
Franko72
Join Date: May 2004
Location: Cincinnati,Ohio
Posts: 471
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I did the same thing and found that the prop valve was bad.
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![]() 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 |
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#29 |
Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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Blew air throught the front lines with no problem today. All signs point at the proportioning valve.
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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 |
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#30 |
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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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. |
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#31 |
Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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Is the brake light controlled only by the position of the prop valve or only pressure?
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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. |
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#32 |
Registered User
Join Date: Jun 2002
Location: central pa
Posts: 1,525
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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.
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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 |
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#33 |
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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The light is controlled by the valve.....and the valve is controlled by the lack of pressure on one side or the other.
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#34 |
Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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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. ![]()
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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 |
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#35 |
Registered User
![]() Join Date: Jan 2004
Location: HERNDON VA
Posts: 216
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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 |
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#36 |
Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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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?
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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 |
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#37 |
Registered User
Join Date: Nov 2007
Location: DFW, TX
Posts: 32
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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?
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#38 |
Registered User
Join Date: May 2004
Location: Topeka, Ks
Posts: 2,293
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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
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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. |
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#39 |
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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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.... |
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#40 |
Registered User
Join Date: Nov 2007
Location: DFW, TX
Posts: 32
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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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#41 |
Senior Member
Join Date: Jan 2007
Location: central pa
Posts: 428
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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
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#42 | |
Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
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Re: Proportioning Valve
Quote:
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56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
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#43 |
Gettin By on Gettin By
Join Date: Jan 2008
Location: Cedar Creek, Tx
Posts: 1,033
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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.
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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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