Originally Posted by BillGrissom

Having fooled with boosters on different cars, I'll speculate. Most 60's U.S. cars had a thick booster like the 300SD. Those have an internal rubber bellows that seals the vacuum. I put a 99 Breeze booster on my 65 Dart and it looks like the 300SD one. I recall it has the internal bellows. Some later boosters like the 300D and those on my Chrysler minivans are flat, pancake type. They don't have the bellows (I think) and seal the vacuum w/ the MC body. The advantage is they are short, disadvantage is that brake fluid leaks past the piston get sucked into the booster (both my 300D's "as found"), plus you must insure the MC seating gasket seals tight.

Re DOT 5 (silicone) fluid, I converted all my cars to that, except 2 newer ones w/ ABS. If you research enough, you will find that the warnings about mixing with glycol fluids (DOT 3, 4, 5.1) is unfounded and probably something the lawyers make them put on the labels. Anyway, I converted all mine when rebuilding the system and always blew out the lines, then ethanol, then blow good again and let sit. I didn't want any drops of old, rusty glycol to cause problems. I recently took the MC out of one car I converted to DOT 5 15 years ago and it was pristine inside. I only removed it because converting from a single pot (1965 car) to a dual reservoir MC. I had ample problems with rusty glycol in the past, especially when I lived in humid Georgia, and none since changing to DOT 5. In my remaining glycol cars I try to flush the brake fluid every 2 years, and it still comes out a bit rusty.