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

chadcampbell00 · 02-05-2013, 09:34 AM

I bought a '70 Jimmy a few weeks ago and the rear breaks have a tendency to lock up at more sudden than normal breaking. It's pretty bad on gravel and causes the rear end to slide sideways. The previous owner installed all new braking components (booster, master cylinder, drums, shoes and the rubber lines). It has drum brakes front and rear. I noticed that it has a proportioning valve but I thought only vehicles with front disk brakes had that. I'm not real familiar with proportioning valves so if anyone is I could use some advise. Did these models come factory with them or was it added? Should I replace it or bypass it? I have seen some adjustable ones online, should I try one of those? Or maybe my problem has nothing to do with that. Both rear wheels lock up so I don't think it's a cylinder problem and they should be self adjusting. They release when I let off the brake so I don't think they are too tight anyways. Any advise?
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cleszkie · 02-05-2013, 07:17 PM

Before you go bypassing or replacing things, check that the rear brake shoes were installed properly. Each pair of shoes has one with a shorter length of brake lining and one with a longer length of brake lining. If my memory serves me, the shoe with the longer brake lining should be installed in the forward position on the backing plate. If this is reversed, the drum brakes can have a tendency to lock up. If I have this backwards, hopefully someone here will correct me. I swapped in disc brakes on the rear a while back, and have let all my drum brake knowledge dwindle.

pound41 · 02-05-2013, 09:46 PM

it had a prop valve on it when it came from factory. I don't think it had a bleeder on it. I would look at adjustments on the drums etc before I start swapping out valves

chadcampbell00 · 02-05-2013, 10:15 PM

Thanks. I had my tires balanced the other day and while they had them off I took the brake drums off just to take a quick look. They both came off with ease so I don't think that they need adjusting but I'm gonna double check that anyways. I will also take them back off and make sure the shoes are on correctly.
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02-05-2013, 09:34 AM	#1
chadcampbell00 Registered User Join Date: Jan 2013 Location: Holden LA Posts: 76	Proportioning valves I bought a '70 Jimmy a few weeks ago and the rear breaks have a tendency to lock up at more sudden than normal breaking. It's pretty bad on gravel and causes the rear end to slide sideways. The previous owner installed all new braking components (booster, master cylinder, drums, shoes and the rubber lines). It has drum brakes front and rear. I noticed that it has a proportioning valve but I thought only vehicles with front disk brakes had that. I'm not real familiar with proportioning valves so if anyone is I could use some advise. Did these models come factory with them or was it added? Should I replace it or bypass it? I have seen some adjustable ones online, should I try one of those? Or maybe my problem has nothing to do with that. Both rear wheels lock up so I don't think it's a cylinder problem and they should be self adjusting. They release when I let off the brake so I don't think they are too tight anyways. Any advise? Posted via Mobile Device

02-05-2013, 07:17 PM	#2
cleszkie Registered User Join Date: Feb 2003 Location: Santa Ana, CA Posts: 2,191	Re: Proportioning valves Before you go bypassing or replacing things, check that the rear brake shoes were installed properly. Each pair of shoes has one with a shorter length of brake lining and one with a longer length of brake lining. If my memory serves me, the shoe with the longer brake lining should be installed in the forward position on the backing plate. If this is reversed, the drum brakes can have a tendency to lock up. If I have this backwards, hopefully someone here will correct me. I swapped in disc brakes on the rear a while back, and have let all my drum brake knowledge dwindle.

02-05-2013, 09:46 PM	#3
pound41 Registered User Join Date: Dec 2002 Location: Northern Virginia Posts: 1,268	Re: Proportioning valves it had a prop valve on it when it came from factory. I don't think it had a bleeder on it. I would look at adjustments on the drums etc before I start swapping out valves

02-05-2013, 10:15 PM	#4
chadcampbell00 Registered User Join Date: Jan 2013 Location: Holden LA Posts: 76	Re: Proportioning valves Thanks. I had my tires balanced the other day and while they had them off I took the brake drums off just to take a quick look. They both came off with ease so I don't think that they need adjusting but I'm gonna double check that anyways. I will also take them back off and make sure the shoes are on correctly. Posted via Mobile Device



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