I have been experiencing a consistent problem with the brakes on my 1966 122. Here is what happens. Upon pushing the pedal initially, the pedal travels 3/4 of the way to the floor before the brakes engage. A second "pump" brings the engagement back to where it should be. I have bled the brakes several times. I have replaced the flex hoses. I have replaced the rear cylinders with 1" cylinders from IPD. I have verified that the front calipers are not stuck and that the pads are in good shape. The rear shoes have plenty of lining on them.
At first I thought that the rear drums were out of adjustment. However, after adjusting the shoes towards the drums, the drums became very hot and I had to back them off. They are currently adjusted in a manner consistent with the manual.
I have developed a theory about the cause of my problem and would like to hear if anyone here thinks it is reasonable. In addition, I would appreciate any ideas you may have about how to correct this problem.
Here is my theory. When I ordered the cylinders from IPD, there was a notice explaining that the orginal bore (I think it was 7/8") was no longer available. Because of this, IPD said that both rear cylinders would have to be replaced at the same time with 1" cylinders. If each wheel cylinder has 1/8" greater diameter than the original cylinders, am I correct to assume that the rear brakes now require a volume of brake fluid that is 25% greater than original to engage the shoes fully? This would certainly explain the excessive pedal travel. After the initial "pump" if another "pump" is performed before the return springs return the cylider to its original position, the braking would seem normal.
Would it be possible to fabricate some type of shim to place between the cylinders and the shoes to compensate for this?