Thread: Big or small line to the front brakes? (3/16 or 1/4")

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The reason hydraulic brakes work so well is because the pressure at any point in the whole system is always the same! Big line, small line, it makes no difference. If the brakes wear some, the pressure is still the same at all places. If the brakes get hot, the pressure is still the same. If this weren't true, the car would swerve left or right when you stepped on the brakes, depending on which side of the car the sun was shining on!

When you plumb the master cylinder, you need to determine how the tubes were arranged in the car the master came out of. It makes a difference because of the balance spring inside the master cylinder, that's located between the front piston and the rear piston. You can usually tell by the size of the reservoirs. If a master cylinder is from a car with front disc brakes, the reservoir for the front wheels will be larger than the reservoir for the rear wheels. This is because disc brakes draw more fluid from the reservoir as the brake pads wear, but drum brakes do not draw more fluid as they wear. The automatic adjusters in drum brakes make up for the wear, rather than the wheel cylinders. Master cylinders from cars with 4 wheel drum brakes have equal size reservoirs, so it's harder to figure out.