that 400% thing is based upon the statement 'only increases the potential of non-piston retraction'. So here is the logic...as most folks who work on their own brakes know, the old piston retraction is problematic. It may go or maybe not, SAAB Turbos ate front calipers like peanuts..anyway...so say the #1 piston retracts nicely, great..that's 100% good, or 100% bad if it goes the other way. However, there are still three more to hope for the same result, #2 goes well excellent, now you're to 200% and so and so forth...and if one refuses to cooperate well, then the entire gang has to go...and this only on one assembly....that's my 400% theory thing.....