I just finished writing an article that describes how to disassemble the combination brake valve that was used after January 1, 1970 for vehicles equipped with front disk and rear drum brakes. Here's a link to the article:

http://www.musclecarresearch.com/1970-76-mopar-combo-valve-autopsy

I'd appreciate any insights, additions, or corrections to make the article more useful. I'd especially like to know if anyone has ever found a small spring at the bottom of the pressure differential portion of the valve.

Scott
Nice work. As you note this combo valve includes both tee and proportional mechanisms, and looks like it has mostly the same internals as the individual valves.

I haven't taken one of these apart, but it would seem the spring you mention would be needed to mechanically balance the warning lamp circuit. Otherwise the "barbell" (piston) would not have equal resistance on that side of the circuit.?.

Something you may want to address on your site in more detail is the mating of new, sometimes stainless, brake lines with original brass valves. The valve nipple has been previously deformed by the original steel lines and, at least in my experience, is prone to leaking when re-mated with new lines (or perhaps even the original lines). The Inland Tube site mentions this and recommends a loosen-tighten sequence with new lines. I have found several loosen-tighten sequences will cure a leak more effectively than muscling the fastener.

Yeah, that missing spring makes me wonder. Ford's pressure differential valves are designed to float, but they don't have springs on either side. A spring on only one side doesn't make sense. I know the repros include a spring.

I can think of three possibilities:

• There never was a spring.
  
• There was a spring, but it has completely rusted away.
  
• All three of the valves I've disassembled were opened before and the spring was lost.
  

I'd like to believe that maybe the spring rusted away, but even then I'd expect to find some small rusty remains.

That was my guess...spring rusted away.

I actually think there was a design change to the valve that eliminated the lower spring to help re-center the piston. It would not just rust away in all 3 valves and one of the valves came from my 30k mile car that had perfect brakes. I actuallty changed to a repro valve cause the orig leaked when I installed new lines as told in the post above. The new valve has been leak free for 2 years now.

I think I might have stumbled across something: could it be that this is a situation where different suppliers (Weatherhead and Kelsey-Hayes) produced interchangeable valves with slightly different internal parts? The valves I've disassembled were produced by Weatherhead. I just found some pictures of a Kelsey-Hayes valve posted by bigblock340power in another thread:

https://board.moparts.org/ubbthreads/showthreaded.php?Cat=0&Number=6923491&page=0&vc=1

Notice the differences in the pressure differential piston and spring assembly!

I've had a chance to examine a Kelsey-Hayes valve and can confirm that it matches the service manual drawings. Having seen both I've also been able to write an article that describes how to rebuild both valves:

http://www.musclecarresearch.com/1970-76-mopar-combo-valve-rebuild

I have a seal kit available that I'll post in the classifieds. Thanks to all of you that have helped by letting me take a look at your valves.

I'm sure there are other cars that used this type of valve, but I don't have a parts manual that covers these years. Please clue me in if you know of other applications.

Scott,

I'm pretty sure this is the same valve for 72 B-bodies. You may want to post your ad in the B-body parts section as well.

Mike.

Thanks for the info, Mike. My 1971 parts manual doesn't seem to include this valve at all, which seems strange if it was introduced during the 1970 model year. Do you know if there's a parts manual available that includes a description of this valve?