Ok I'm back. It has been my understanding that (everything else being the same), using a bigger bore master cylinder than stock normally results in less pressure output to the wheel cylinders, so in fact it's harder to push down and results in less pedal travel since a bigger bore can push a greater amount of fluid with less movement of the pedal.
I mentioned this because all this time, I thought I had a 1-inch bore m/c, when in fact what I have is an undersized 15/16-inch bore. Now, I understand as well that an undersized m/c will do the opposite, create a higher pressure output, which is nice of course, but result in a longer pedal travel, because of the smaller bore of the m/c, which takes longer to fill up the wheel cylinders.
I decided to check old notes I made from 10 years ago, and discovered that the jeep in fact only had an extremely undersized 3/4-inch m/c ! I now somewhat recall having to pump up the pedal like maybe 4 or 5 times, before the brakeshoes caught on firmly to the drum, a mere 2 or 3 inches away from the floor. As low as the pedal was, it felt firm and solid (as opposed to being spongy). I believe it was pulling a big water tank very, very slowly around some big private piece of land, hence the owner being satisfied with the dangerously low and slow responding brakes. And this was with the 1-inch wheel cylinders on all four drums.
I apparently changed the 3/4-inch m/c to what I thought was a 1-inch one, but was in fact 15/16-inch (still undersized). The pedal took less strokes this time (2-3 pedal pumps) to get the brakeshoes to firmly contact the drums, and was a few inches higher now ! In both scenarios of the 3/4-inch and 15/16-inch m/c's, there was no spongy feeling on the brakes.
Given what I experienced, I figure I can either find the correct 1-inch sized m/c, or get the smaller 3/4-inch rear wheel cylinders (cheaper to do) either of which should reduce the number of pedal pumps and get the pedal higher sooner, because the wheel cylinders will fill up sooner.
Rus Curtis - I checked a couple of Willys jeep online stores and saw that it was only the rear wheel cylinder of the CJ3B that looked like mine, and that the fronts were totally different looks wise, though as you said, the front and rear backing plates had the same part number. The pistons for the front by the way didn't seem to have the notch for the brakeshoes to mate with. Whereas the CJ3A wheel cylinders I saw had notched pistons for both front and rear, as well as the exterior looking identical to each other.
This being the case, I would still appreciate it if a CJ3A owner could please confirm if the front and rear wheel cylinders are interchangeable, same distances of mounting holes and bleeder valve ? Maybe you could verify as well if the front and rear backing plates have the same part number? That would be most appreciated ! Thanks again.
