20 replies to this topic

[JNJ]

Brake fluid is not compressible, air is and so are brake pads.  Also, steel bends.  If you are sure you have the air purged from the system, and you have stock brakes (more on that later) you have something bending or soft/compressible pads.  I can tell you that Carbotech pads compress more than Hawk DTC pads and new pads that have not been bedded are softer than bedded pads.  As for steel bending, any misalignment of a caliper bracket (like a lot of remans have due to cores from totaled vehicles) will flex.  The force applied by the caliper is enough to bend the bracket and let the caliper align but it takes pedal travel to do it.  The bracket is stiff enough to return sending the piston back into the bore.  The easiest way to tell is to loosen all of the caliper bracket mounting bolts (like 1/2 turn after they are free) and apply the brakes.  If the pedal is normal, tighten them one at a time and check the pedal.  When you come to the one that is causing the problem, the pedal will be low.  Have someone apply the brakes and look for movement.

 

If your brakes are not stock, you have a bit more of an engineering problem.  Things like master to piston area, booster gain and pedal ratios will drive you nuts.  Change the master bore size 1/8" larger and the pedal feel (solid) will increase, travel will decrease and braking power will decrease.  Go the other way and make the master bore 1/8" smaller and the the situation goes the other way.  Same is true for piston size changes and larger boosters.  Add 5" to the brake pedal length and the travel will increase, pedal feel (mushy) will decrease and power will increase.  Fortunately when Mazda made the brakes larger they used the same master and calipers and just changed the rotor diameter and the pads area. 

 

I have done these evaluations while working for an OE, there is a lot to getting the brake feel right and it is different for different customers.  My car has a very high and solid pedal that came from very true pedal brackets and perfectly aligned ears on the front and rear knuckles.