Difference between the 851 black and Gold brembo front front calipers

Bambara

Can anyone tell me what is the technical difference between the earlier black coloured, and the later gold coloured Brembo front brake calipers?

brad black

black have 4 x 32mm pistons an gold are 2 x34mm and 2 x 30mm? i rebuilt my 89 black ones and the pistons were all the same size.

Bambara

brad black wroteblack have 4 x 32mm pistons an gold are 2 x34mm and 2 x 30mm? i rebuilt my 89 black ones and the pistons were all the same size.

Brad, thanks for this info. I am told the later configuration is better, but why is it so?
What diameter brake piston has first contact with the advancing rotor?

brad black

i think the small one is at the rear side of the caliper. possibly because the disc drags the rear edge of the pad and that force tries to angle the front of the pad away from the disc, and a larger piston at the front can give more force at the front to keep the pad flat against the disc across its full width. dunno, could be making shit up.

lefty

I thought the smaller piston is at the front, to reduce brake noise and prevent wedge-wearing of the pads...??

brad black wrotei think the small one is at the rear side of the caliper. possibly because the disc drags the rear edge of the pad and that force tries to angle the front of the pad away from the disc, and a larger piston at the front can give more force at the front to keep the pad flat against the disc across its full width. dunno, could be making shit up.

Peter888

Brad is spot on. You should always put the smaller piston in the location that contacts the rotating disc first, due to the twisting moment that the pad friction causes, which loads up the leading edge. Back in old drum brake days this "self-servo" effect was used to increase the effective lever ratio of the brakes because leading shoe drums self-servo onto the brake drums.

My other hobby is Mazda RX-8s. Some aftermarket firm decided to supply multi-piston callipers (AP knock offs) for the car, but they didn't understand this effect, so they made all the callipers with the large piston on the leading edge. It took just a few weeks for people to start reporting seriously wedge-shaped pads. And, of course, this then put huge sideloads into the pistons, potentially locking them in their bores. The company never did fix the issue, so the owner's club did it... Moral of the story: Never buy cheap brake parts from dodgy suppliers you've never heard of before!