Oh boy
FIRSTLY
> IF the brakes slow the car as you would expect, and
> IF you can lock the front brakes to skid the tires at say 20 mph, and
> IF the pedal does not sink on it's own, while you are holding a constant pressure on it, with the engine OFF, and the booster relaxed;
> THEN the M/C is working.
SECONDLY
IDK how many times it's been said;
In the Time period from 67 to IDK/maybe the late 80s, as regards A/F bodies; Year for year, there is no meaningful mechanical differences in the guts, between a disc/drum M/C, and an all-drum dual M/C.
The only Meaningful differences are; the sizes of the bores, the sizes of the reservoirs, the use of the little hold-off (residual)valves, and the rod-retention system. They can all be swapped amongst eachother, so long as the disc brake port never has a working residual valve in it.
And yes, I know about the different down-stream, brake control valves.
To answer your question,
riddle me this;
During installation, did you have to compress the pedal-rod into the booster to fit the brake-pedal retaining bolt?
If no, then don't bother trying to change the length of the pedal-rod. But-um
If yes, that ain't right;
and the next questions are;
1) has the engine been changed from 6-cylinder to 8-cylinder, and if yes, then
2) was the car originally a 9" brake car? and if yes, then
3) is the brake pedal still from the 6-cylinder car?
4) the point is that the six-cylinder pedal ratio is different from the Disc/drum set-up.
5) If you need it, I can supply a pedal set-up, that I took off a 1973 Dart with Power front-discs and 10" drums on the back.
Now then,
as to adjusting the pushrod length on the firewall side; between the M/C and the booster;
Quick lesson;
>This rod must be adjusted after the booster is installed................ because, we gotta know where the control valve is fully closed.
>this rod must be short enough so that the guts of the M/C are parked at back of the chamber, to expose the Compensating port. If the C-Port is not thus exposed, but the M/C is otherwise functioning correctly, then; the brakes will work fine. But the pedal will continuously, over time, drop, as the fluid in the lines is not being continuously replenished at the C-port. Then one day, the pedal is so low that one or the other end of the car can no longer brake for lack of fluid pressure.
> If this rod is sloppy loose, it will take a lot of pedal-travel to begin pushing the Power-Pistons down the road. The control valve in the booster is desperately trying to provide assist, but until the slack is taken up, it can't do a doggone thing. Even then, until the power-pistons get there work done of pushing fluid down the road, still nothing is going on.
Then, suddenly, the pads hit the disc and the shoes hit the drums and the power-pistons are finally giving feedback to the booster and
BAM!
the booster is in full attack mode.
Moral of the story; the pushrod is better if a lil short, than if a lil long, BUT
don't let the pushrod be too short.
Knowing this now, you can, in a narrow window, customize the brake action, by adjusting that pushrod, until you like it.
I'da told you this first, but then, you wouldn't have learned much. But now, every time you get into your Dad's old Dodge whatever, and hit the windshield on the first brake application, you'll know why that's happening, and how to change it.
