Vented brake idea

[phyrman]

Sorry for the poor pictures The first pic shows the 11.75 in a 15x6" rim
second pic older 10.25 in a 15x6" rim.......poor car has been sitting out the past 2.5 years

 

[Bill Blue]

https://www.wilwood.com/Calipers/CaliperProd?itemno=120-8925

A piston area of 4.45 square inches corresponds to a piston diameter of 2.375 inches.

In any case, the difference in piston area between a 2.375" and 2.500" piston diameter is less than 11%. Did your problem with 2.500" bore GM Metric calipers happen to also involve the use of a 6:1 ratio brake pedal which results in a shorter than normal master cylinder stroke (and volume)?

While the two are tied at the bellybutton, the 2.5" caliper bottomed out on the master cylinder then in use, I'm thinking it was .75". Regardless of sizes involved, my next MC resulted in a firmer than desired pedal, which prompted the 6:1 pedal. Can't recall the exact stops along the way. I do recall that when I "refreshed" the old 2.375 junkyard calipers with new ones, the mascara hit the fan and it took me a long time to determine the cause, new replacement calipers that were purchased as 2.375 but were 2.5", as were the second round of new calipers. Difference was not huge, just enough to cause the pedal to bottom out during an emergency stop. Yes, I knew I walking a fine line, but knew enough reject anything that hinted of trouble.

Bill