Does a proportioning valves go bad? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

crm318 · 02-14-2013, 06:46 PM

I was bleeding my brakes on my 72 cheyenne the other day and i noticed that the pedal was soft. The rear wheel cylinders barley had any fluid coming out, just a trickle. no fluid seemed to be coming out of the wheel cylinders on the drum side. I was thinking it was the proportioning valve. Do those things ever go bad? I thought it was just a manifold that distibuted fluid. Can they be serviced/cleaned? I was also thinking about replacing master cylinder while im at it. Could that be the culprit?

SS Tim · 02-14-2013, 07:42 PM

On a 71-72 it is a pressure proportioning valve and lamp switch, reducing pressure to the rear cylinders as compared to the front calipers. Did you clip the prop. valve while bleeding? Probably should think about the condition of the rear brake hose first. Both brakes are feed through it and they do deteriorate. Also with the hose off at the frame end you can verify flow at that point. If you don't have factory manuals download them to make your life easier.

**special-K** · 02-14-2013, 08:35 PM

Not sure what your brake problem is,but to answer your question,yes,a proportioning valve can go bad.

crm318 · 02-14-2013, 10:49 PM

Thanks guys. I have the day off tomorrow, so I will give it a look and tell yall what I find.

02-14-2013, 06:46 PM	#1
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Does a proportioning valves go bad? I was bleeding my brakes on my 72 cheyenne the other day and i noticed that the pedal was soft. The rear wheel cylinders barley had any fluid coming out, just a trickle. no fluid seemed to be coming out of the wheel cylinders on the drum side. I was thinking it was the proportioning valve. Do those things ever go bad? I thought it was just a manifold that distibuted fluid. Can they be serviced/cleaned? I was also thinking about replacing master cylinder while im at it. Could that be the culprit? __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

02-14-2013, 07:42 PM	#2
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: Does a proportioning valves go bad? On a 71-72 it is a pressure proportioning valve and lamp switch, reducing pressure to the rear cylinders as compared to the front calipers. Did you clip the prop. valve while bleeding? Probably should think about the condition of the rear brake hose first. Both brakes are feed through it and they do deteriorate. Also with the hose off at the frame end you can verify flow at that point. If you don't have factory manuals download them to make your life easier. __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban Last edited by SS Tim; 02-14-2013 at 07:51 PM. Reason: higher word count

02-14-2013, 08:35 PM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Does a proportioning valves go bad? Not sure what your brake problem is,but to answer your question,yes,a proportioning valve can go bad. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

02-14-2013, 10:49 PM	#4
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: Does a proportioning valves go bad? Thanks guys. I have the day off tomorrow, so I will give it a look and tell yall what I find. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies



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