Proportioning valve question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ratrod67 · 10-19-2003, 06:00 PM

I have a 67 that has been swapped to 5 lug and disc from a 70's model Suburban. When ever the brakes were just barely applied they would just about throw you through the windshield. I figured that the proportioning valve was wrong since it was from a suburban so I got one from a 76 Chevy truck LWB. After changing them out and bleeding the system I'm still in the same place. Way too much front brakes and no rear brakes. If the truck is jacked up the rear wheels will still spin even if the brake is applied. Any suggestions?

cableguy0 · 10-19-2003, 06:08 PM

sounds to me like either the rear brakes arent adjusted it needs wheel cylinder or the proporioning valve has been tripped not allowing fluid to go to the rear wheel due to a leak

Denny · 10-19-2003, 06:13 PM

Your front brakes also need 3/16" brake lines not the 1/4" like the drum brakes have. I don't know if this helps any.

ratrod67 · 10-19-2003, 06:15 PM

Sorry, here's more info. The truck has a new booster and master cylinder. If you open the bleeders at the rear wheels there isn't any pressure to force brake fluid out when the pedal is pressed. When the system was apart for changing the proportioning valve I blew through the lines with compressed air so I know there's no blocks in the line. Also all 3 rubber hoses are new. Is it possible I just have 2 bad prop valves?

RON WOODGEARD · 10-19-2003, 06:32 PM

I did the same changeover, Junkyard john went Junkyarding, (pun intended) And came up with a stock prop. valve, Not a problem since then, And I didn't have to change out my lines..

You can buy a new adjustable prop. valve, and it will also solve your problems.

Ron

ratrod67 · 10-20-2003, 03:57 PM

ttt

10-19-2003, 06:00 PM	#1
ratrod67 Registered User Join Date: Sep 2002 Location: DFW Texas Posts: 2,270	Proportioning valve question I have a 67 that has been swapped to 5 lug and disc from a 70's model Suburban. When ever the brakes were just barely applied they would just about throw you through the windshield. I figured that the proportioning valve was wrong since it was from a suburban so I got one from a 76 Chevy truck LWB. After changing them out and bleeding the system I'm still in the same place. Way too much front brakes and no rear brakes. If the truck is jacked up the rear wheels will still spin even if the brake is applied. Any suggestions?

10-19-2003, 06:08 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	sounds to me like either the rear brakes arent adjusted it needs wheel cylinder or the proporioning valve has been tripped not allowing fluid to go to the rear wheel due to a leak __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-19-2003, 06:13 PM	#3
Denny Registered User Join Date: Jul 2002 Location: Cedar Hill, MO Posts: 426	Your front brakes also need 3/16" brake lines not the 1/4" like the drum brakes have. I don't know if this helps any. __________________ 1969 Chevy C10. Dakota Digital Gauges, 383 Votex Engine, MSD 8361 Distributor, MSD 6A Unit, Demon Carb, Phoenix Transmission 4L80E trans, 3:73 Posi Rear End Early Classics 6 Lug Disc Brakes and Spindles All Stainless Lines

10-19-2003, 06:15 PM	#4
ratrod67 Registered User Join Date: Sep 2002 Location: DFW Texas Posts: 2,270	Sorry, here's more info. The truck has a new booster and master cylinder. If you open the bleeders at the rear wheels there isn't any pressure to force brake fluid out when the pedal is pressed. When the system was apart for changing the proportioning valve I blew through the lines with compressed air so I know there's no blocks in the line. Also all 3 rubber hoses are new. Is it possible I just have 2 bad prop valves?

10-19-2003, 06:32 PM	#5
RON WOODGEARD Resident Young Old Dude ! Join Date: Jul 2001 Location: Nevada Posts: 1,948	I did the same changeover, Junkyard john went Junkyarding, (pun intended) And came up with a stock prop. valve, Not a problem since then, And I didn't have to change out my lines.. You can buy a new adjustable prop. valve, and it will also solve your problems. Ron

10-20-2003, 03:57 PM	#6
ratrod67 Registered User Join Date: Sep 2002 Location: DFW Texas Posts: 2,270	ttt



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