|The MGA With An Attitude
Brake CALIPERS Do Not Work When New - BT-140
On Oct 7, 2016, Steve M in Valhalla, NY, USA wrote:
"Even when wife steps on brake outer pad on this left side does not touch rotor. These are reproductions with metric bleeders so I left them as packaged. The brake pedal may have excessive travel. Seems to go pretty far down before resistance. Note how the piston seal on the side that does not touch seems extended while on the touching side it is not".
"Before removing it I used the hydraulics (brake pedal) to push the pistons out a bit but not all the way, as seen in the photo. If I can get the pistons out I'll start buying parts. I put a 0.028 inch feeler gauge in the piston-pad gap and stepped hard on the brakes. My wife was manning the feeler gauge and reported no problem wiggling the gauge despite my pedal stomp. It is still totally loose. The other piston grips enough to hold the rotor still".
Kelvin Dodd from Moss Motors USA offers this tech tip:
"This is a common problem with new, rather than rebuilt calipers. The caliper piston seals bond slightly to the pistons during the time from manufacture to installation. When fitted with new pads, the piston will not slide out from the fully retracted position to the normal static position, but rather stretches the rubber in the seals. When the brake pedal is returned, the pistons are pulled back by the elasticity of the seals to the original fully retracted position which gives too much pedal free play.
"It is a simple process to exercise the pistons. Install either a pair of used brake pads, or a shim that is similar in thickness. Apply the brakes lightly. The pistons will move far enough to slide in the seals. Retract the pistons as you would when replacing pads, install the new pads and the pistons should slide to the correct static position on the next press of the pedal".