Re: [AMC-list] brake proportioning valve

[Jim Blair <carnuck@xxxxxxxxxxx>]

there was also a "combo" valve used that is really the same thing. Pressure differential valve was used on systems with dual master cylinder bores (one big, one small in series in the same unit like my '84 J10 had)


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Subject: Re: [AMC-list] brake proportioning valve
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If the brakes work fine you need NEITHER. What you have to do is go to a WET parking lot (WET, not just damp... or better yet a dirt road), get up to about 40, and slam on the brakes as hard as you can. Observe how the rear brakes lock. If they lock immediately with little effort then you need a proportioning valve in the rear brake line. If they just do lock up with a lot of effort, then you're fine. You want them to lock, but only with just about the greatest amount of effort you can supply and not right away. If all four lock at about the same time you're okay. You mainly don't want the rear locking real easy in a panic stop. If they do you could swap ends if the front wheels get turned any or the road surface slopes one way or the other -- anything to start the rear end sliding sideways.

I researched how AMC used proportioning valves. They were only used on some cars in the mid to late 70s, about a 6-7 year period. Before and after they weren't used. That might not be a big deal, except that Concords used them for a year or two, then didn't. Hornets didn't have them then they did. Apparently there was some experimentation in the 70s -- metering valves for the front disc brakes were used a few years on all models, then only on the big cars, then dropped along with the proportioning valve. Most just copy what the factory did in similar cars just to be safe, but testing your brakes is the best way.
 		 	   		  
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