Originally Posted by RenoE92M3
There is always fluid in the caliper your not filling it every time it only has to move a small amount of fluid. If you are really concerned about it measure the fluid volume in each caliper. How do you think aftermarket brake companies make big brake kits? For the most part they sell the same caliper with different mounting hardware and lines. It's not rocket science it's a BMW guys.
They have the same caliper body but the pistons they put in the caliper are different sized matched to the car it is on.
Believe me, I know what I am talking about. I've ran BBK setups on all sorts of cars. Retrofitted 300ZX 4 piston brakes onto the 240SX. Ran Wilwood big brakes on a Honda Civic... it doesn't work. You need to change the master cylinder, slave cylinder to match the brakes you are using. Even then you end up with uneven F/R brake bias and a whacked out ABS system.
My 240SX with large front 300ZX brakes was crazily front brake biased. I would step on the pedal on track, the front brakes would lock up and the rear brakes would be barely applied at all. It was downright dangerous to drive. The front wheel would lock up and the rear end would step out every time you hit the brake.
What you are talking about would work on an old car before modern brake systems came about. But to put brakes from another car the correct way is to replace the entire brake system with the components from the other car.