Quote:

<snip!> My '71 340 Duster came with K/H (Power) front four piston caliper disc/rear drum brakes. When I bought the car, the power booster was off it. Everything else was intact, and functioning very well. I even plumed in a line lock and went drag racing (I've removed the line lock during this restore). I replaced the org. MC with your aluminum MC you sell here a few years ago. Still everything stopped just fine. My trouble came when, while restoring the car, I replaced the K/H prop./distribution valve with an after market new one I found being sold by a well known Mopar parts vender. When I got everything back together and tried to stop the car, it just didn't want to stop very well. It felt like I just didn't have enough pressure to the Calipers/ drums to do a good job. I pressure bled the system (twice), and bench bled the MC. The peddle felt great, no slop, or fade. I can power out of the brakes, when fully applied (never been able to do that before). My question: given all the variables I described above, could the prop./distribution valve be the culprit? I have since rebuilt me K/H prop. valve (mostly just cleaning it up real well), and intend to place it back into the system to try it again. What do you think?
Thank you,
mike


This Chinese stuff can (and does) have all kinds of bizarre defects. But also be sure that the plumbing to the valve is correct. And, I'd sure bleed one more time -- try a different method, maybe. Remember that the master must be bled before any of the wheels, and if you allow either reservoir to go dry, it must be bled again. I can't visualize a valve defect that would result in a soft pedal, which seems to be what you are describing.

You didn't say whether you re-installed the power booster. If you replaced it, I hope it is one intended for PDB. Otherwise booster runout is a possibility. Me? Manual all the way. Much easier to threshold brake. Threshold braking

Your term "distribution valve" may mislead some. As was mentioned by others above, the front and rear circuits are totally independent and disconnected - fluid NEVER flows from the front circuit to the rear, or vice-versa, under any conditions. The ONLY function of the "valve" (it isn't) on all-drum cars is to turn on the idiot light when there's a pressure differential -- a Federal requirement starting in 1967.

On the master cylinder bias quandary...you'll note that the bore dimension given is singular - meaning, straight bore. There can, therefore, be no pressure differential or proportioning built in to the master (excluding the '90s / 00s stuff with valves that screw right into the master cylinder, of course). I believe those numbers refer to the maximum total volume of fluid that can be pumped from each section of the bore. All that's in a dual-circuit master (at least Mopars) is a primary piston, and a second floating piston. One outlet is between the pistons, the second is behind the secondary piston. Yes, due to friction, etc., there might be a 1% (or less) pressure differential, but that's it! Hook up gauges and see.

The MP masters were just ~'80s truck masters, the later angled-reservoir ones were '90s/00s truck.)

Rick