73 Manual Disc/drum Master cyl no residual valve

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player1up

player1up

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So I did the 8.8 explorer rear w / discs swap a few months ago and I'm just to the point of driving it and have noticed that ( although stops ok ) seems biased to the rear. Feels like stopping a fwd car with the e brake a little.

Car is a 73 Duster that had manual disc/drum setup.
Here is the kicker...Neither the current master cyl OR the old one on the shelf have residual valves in the outlet for the rear brakes. I've even taken the old one apart to see if it's part of the plunger setup and it's not. There was no spring or plunger behind either seat

Am I losing it?

I'm not opposed to getting a new master cyl.

Just to be clear, all of the proportioning happens in the proportioning valve, correct? or is any of it done in the master cyl itself?

I suppose I'll just get an adjustable proportioning valve ( probably some new lines and master cyl as well ) , but I'm just really confused as to why the old MC's don't have the valves..
 
...the newer drum wheel cylinders have large springs inside to maintain pressure on the cups.
..Residual valves are not req'd.
 
ah, ok that makes sense. Guess I'll just need an adjustable valve to get the feel where I like it.
Thanks
 
..if your rear wheel cylinders are 15/16" a change to 13/16" may work.
a bigger rear tire can help as well.
 
ir3333 said:
..if your rear wheel cylinders are 15/16" a change to 13/16" may work.
a bigger rear tire can help as well.
Click to expand...

I actually did that before I swapped to the explorer disc axle but it's no longer drum in the rear.
I was looking into how to "adjust" a factory proportioning valve. I suppose one could play with spring rates in the valve, but having to take it apart and bleed the brakes every time, it's not worth the effort when I can get an adjustable valve for <$50.
I was just hoping for an easy win...no such thing in the mopar world :lol:
 
i've welded the holes closed in the banjo bolt and re drill it smaller. worked fine. do your testing on a wet road you'll be happy.
 
That wouldn't reduce pressure, just flow in both directions.
I guess his would allow the rear brakes to come in a little later than with the larger holes and if the bias was just a tad off, this would work.
From what I've been reading a proportioning valve remains open until a set pressure has been met then closes off completely much like a fuel pressure regulator behaves.
Exploded diagrams seem to support this.

In theory one could reduce the main spring rate to reduce the pressure required to shut the valve, but again, unless someone has a matrix on what spring rate equals what pressure the testing time required to mod the original would quickly overrun the cost of an adjustable valve.

My adjustable valve should be here Monday
 
Took me a minute

You DO have 4x disks, right? Why are you worried about residual valves. Disk brakes should not have 'em

But I agree, at this point I'd say an adjustable valve.

I only got my car together for a bit this summer with the 4x disks (Versailles rear, 73/4 Duster front) and it seems fine with NO prop valve, but of course tires, etc, all affects this.
 
67Dart273 said:
Took me a minute

You DO have 4x disks, right? Why are you worried about residual valves. Disk brakes should not have 'em

But I agree, at this point I'd say an adjustable valve.

I only got my car together for a bit this summer with the 4x disks (Versailles rear, 73/4 Duster front) and it seems fine with NO prop valve, but of course tires, etc, all affects this.
Click to expand...

Yeah, its disc/disc now. Pedal is firm and the brakes stop just fine but don't "feel" right. Maybe I haven't driven it enough to get used to it or maybe I'm a little paranoid. When it comes to brakes, one almost can't be too paranoid.
I did confirm that the rears aren't dragging before I drove it. The only reason why I was concerned with the residual valve was because I didn't check before now. When I didn't find it I was confused as to why.
I also cleaned the proportioning valve when I redid the entire brake system but that was a few years ago. The valve system was completely frozen up at that time and the rears would lock before the fronts.
 
I have never seen a residual valve either, but perhaps they were only in disk/drum cars. As stated, the metal cups on the ends of the wheel cylinder springs supports the rubber cups, eliminating the need for a residual valve. Sometimes the spring wire is wound to form a "cup" for same effect.

All MC's I have seen have the same bore for front & rear brakes, so the pressure is the same up to the "imbalance switch" which lights the warning lamp if not true (when it works). The prop valve then reduces pressure to the rear drums (if front disk car). Both are in the factory "combination valve", along with a "hold-off valve" on the fronts.

I bought 2 adjustable prop valves for <$30 ea on ebay in last few years.
 
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