bbc-olds said:
Further research revealed that it now has 7/8 rear cylinders instead of the 3/4 that came on the car. Would that not have a effect on pedal travel in addition to the calipers? Car has 65000 original miles and I assume it has the original calipers. Can they be rebuild into non low drag pieces?
Though the 7/8" wheel cylinders are substantially larger than the 3/4" wheel cylinder, the amount of fluid needed to operate either one is very little compared to a caliper.
It is highly unlikely that its the larger wheel cylinder is causing your issues.
Do you have the stock prop valve installed on the frame?
If you do not, you will need a 2lb residual valve for the front brakes and a 10lb residual valve for the rear brakes. An adjustable prop valve is also recommended to dial in your brake bias.
If you brake calipers are stock, they are LOW drag and will not work with a 7/8" bore master cylinder causing NO pedal at all.
Are your rear drum shoes adjusted out against the drums? This will cause no pressure or little pressure when brake pedal is pressed with your foot.
Do you have enough pedal travel to operate the master cylinder? Master cylinder piston should be about 7/8" to 1.0" in travel. If you have a 6 to 1 pedal ratio, your pedal will travel about 6 inches. If it is less than this, then you are not getting the volume needed to the calipers to operate them effectively.
Do you have the stock 30 year old rubber lines? Rubber lines deteriorate over time and will balloon causing excessive pedal travel. Replace them with new rubber lines (cheapest) or replacement stainless steel flexible brake lines.
To maximize your manual brakes, run 100% organic pads and shoes with an FF rating. Organics have better friction properties at lower temperatures. They require very little heat to operate effectively compared to Semi Metallics and Ceramics which require more heat to operate. If you are using Semi Metallics or Ceramics, this will require more pressure to stop the car (compared to Organics) to stop the car until the brakes get to a certain temperature. Though organics do not like big temperatures for sustained period of time, organics are good for a daily driver or drag car because the pads will not see extreme heat for extended periods of time during their use.
Lastly, your master cylinder may be bad. Even new and rebuilt master cylinders are not known for their reliability.
Does you car stop? I ask this question to say that a manual brake equipped cars will have a long pedal stroke. Smaller master cylinders need longer pedal strokes to move the volume of brake fluid to operate the calipers effectively.