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12-28-2005, 09:51 PM
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#1 |
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Registered User
Join Date: Mar 2005
Location: Castle Rock, CO
Posts: 24
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Disc Brake Proportioning Valve Problems
I have a 1972 GMC K1500 with power disc brakes. The brakes were terrible so I started replacing almost all of the major components of the system. The old master cylinder had the front chamber plumbed to the rear portion of the proportioning valve and the rear was visa versa. I have since changed it to the configuration in the picture where the front chamber feeds the front of the valve. Is this correct?
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1972 GMC K1500, sbc 350, turbo 350 Castle Rock, CO |
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12-29-2005, 12:40 AM
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#2 |
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Senior Member
 
Join Date: Sep 2005
Location: Lewisville, Nc
Posts: 10,233
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Re: Disc Brake Proportioning Valve Problems
looks right to me
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David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube |
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12-29-2005, 01:47 AM
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#3 |
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Registered User
Join Date: Mar 2005
Location: Castle Rock, CO
Posts: 24
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Re: Disc Brake Proportioning Valve Problems
Thanks for the vote of confidence. Here are two pics out of the service manual and possibly why I am confused. I believe I have a normal 1/2 ton set up, and the pic shows that the way I set things up looks correct. I become confused when I look at the 3/4 ton pic and it looks like the tubes are reversed, like the way I found my current truck b/f I took it apart. Does anyone have any pics of a stock 1/2 ton set up with disc brakes they could post?
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1972 GMC K1500, sbc 350, turbo 350 Castle Rock, CO Last edited by 72 GMC K1500; 12-29-2005 at 03:59 PM. |
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12-29-2005, 02:14 PM
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#4 |
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Registered User
Join Date: Mar 2005
Location: Castle Rock, CO
Posts: 24
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Re: Disc Brake Proportioning Valve Problems
Thoughts????
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1972 GMC K1500, sbc 350, turbo 350 Castle Rock, CO |
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12-29-2005, 04:50 PM
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#5 |
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Registered User
Join Date: Feb 2002
Location: Vacaville, CA
Posts: 2,746
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Re: Disc Brake Proportioning Valve Problems
Yes, check the lines out of the P-valve which go to the front and which to the rear. That should tell you how the master should be connected.
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 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI |
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12-29-2005, 04:55 PM
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#6 |
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You Are Not Forgotten
 
Join Date: Aug 2004
Location: Laurens, SC
Posts: 45
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Re: Disc Brake Proportioning Valve Problems
That's definitely a correct hookup, I have a picture but can't remember how to post it. John
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If you don't know where you are going, any road will take you there! |
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12-29-2005, 05:09 PM
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#7 |
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You Are Not Forgotten
Join Date: Aug 2004
Location: Laurens, SC
Posts: 45
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Re: Disc Brake Proportioning Valve Problems
Here's a pic
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If you don't know where you are going, any road will take you there! |
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12-29-2005, 07:54 PM
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#8 |
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Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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Re: Disc Brake Proportioning Valve Problems
I worked on the brake system on my 72 GMC K1500. I replaced the MC a couple of times, rebuilt the drums (the fronts were good), and bled about a 55 gal. drum through the system. It worked like sh*t until I replaced the booster with a dual diaphram booster. The system works great now.
The story I got from an old local brake guy is that the brake system as originally designed was undersized. The new non-asbestoes pads and shoes are very hard and that adds to the lousy stopping power.
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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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12-29-2005, 08:18 PM
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#9 | |
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Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
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Re: Disc Brake Proportioning Valve Problems
Quote:
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69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
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12-31-2005, 12:17 AM
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#10 |
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Registered User
Join Date: Mar 2005
Location: Castle Rock, CO
Posts: 24
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Re: Disc Brake Proportioning Valve Problems
Thanks for all the good advice. I have not yey completed putting the rear brakes together so I can't give you an update as to how they "feel." I am hoping they will be much improved from before. AVGJOE, when you say you purchased a dual-diaphram booster did you have to ask for a 3/4 ton model?
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1972 GMC K1500, sbc 350, turbo 350 Castle Rock, CO |
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12-31-2005, 02:08 AM
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#11 |
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Custer had a plan too.
Join Date: Dec 2003
Location: No. California
Posts: 344
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Re: Disc Brake Proportioning Valve Problems
I employed the "old crusty brake guy looked under my hood and said, use this one" method.
I can look to see if there is a model # on it. It was about $120.
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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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