Re: [Amc-list] Proportioning Valve

[Frank Swygert <farna@xxxxxxx>]

Felton and Keith:
1. You don't absolutely have to have the proportioning valve. On dry pavement you'll never notice the difference with or without one. In slippery conditions, however, not having one can be dangerous. If the rear wheels lock before the fronts and the car isn't going perfectly straight the rear end can overtake the front. If you know your car and don't panic you can feel this coming and let off the brake pedal slightly. Can you do that in a panic situation, where a kid runs out in front of you or a car suddenly stops or pulls out? Maybe, maybe not. Might not be enough time. 

AMC used a 200 psi proportioning valve in the back for Javelins and smaller cars, 400 psi for Rebels, Matadors, and Ambassadors. You can get an adjustable one with psi settings on it, or use a standard GM combination valve (has brake light switch too) in place of the normal junction block. These are plumbed with a T in the line between the master cylinder and front brake inlet. The line from the T goes to the left front brake, the front brake outlet from the combo valve goes to the right (but you can use a T after the combo valve -- doesn't really matter). Of course the rear brake line goes into the valve then to the rear brakes. The GM valve is common and is set in the 200-400 psi range -- no one seems to know for sure! This valve is commonly used by hot rodders in much lighter cars than the Javelin. www.mpbrakes.com has lots of technical info on their site and sells the GM combo valve as a generic piece. Late 70s and 80s AMC cars use them, and the Jeep XJ Cherokee uses a si
 milar piece. You can get one of those from a salvage yard -- the valve is mounted on the master cylinder, making it easy to remove. 


2. Keith, your problem sounds like the wrong master cylinder (MC) or a MC that is going bad (leaking at the seals internally). Or you could just have air in the lines. Try bleeding first, as air in the lines is the most likely problem.

What MC did you use, and what year disc brake calipers? 77-83 calipers from Hornets and other small cars use a 1" MC. Big cars and 75-76 small cars use a 1-1/8" MC. 71-74 Kelsey Hayes calipers generally use a 1-1/16" MC. Read the tech pages on www.mpbrakes.com -- bore size makes a noticeable difference! 

----------------------
From: <feltonjk@xxxxxxx>
To: <amc-list@xxxxxxxxxxxx>
Sent: Wednesday, October 24, 2007 4:20 PM
Subject: [Amc-list] Proportioning Valve

I am new to the list so forgive me if this subject has been addressed already. I am converting a 70 AMX from drum all the way around to front disc. I have everything I need except the proportioning valve. I have been told everything from I don't need one, to buy an adjustable one (but get a brake professional to adjust it), to use the GM valve that was used on vehicles such as the 70 Impala.? Any suggestions?

AND

Date: Thu, 25 Oct 2007 10:28:20 -0500
From: Keith Evenson <epd@xxxxxxxxxxxx>

Armand, I also installed disc's on the front of my 70 Jav but I did  
not put in a prop. valve. I was advised at the time I did not need it.
The disc's are better then the drums were but I also have a 68 AMX  
with factory disc's and it stops a ton better and faster then the  
Javelin does now. It just seems to be kind of a soft pedal if you  
know what I mean. Just seems like you have to push for a bit before  
they start to grab.  I have ok vacuum like 13 - 15lbs so it seems  
like that isn't the problem but do you know of any thing else that  
may help or does it sound like I need a prop. valve. I know it just  
balances the system so I don't think that is the problem. The other  
thing I was considering is a vacuum tank?

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)


_______________________________________________
Amc-list mailing list
Amc-list@xxxxxxxxxxxx
http://www.amc-list.com/mailman/listinfo/amc-list