Does anyone know the various E34 caliper piston diameters?

[nuclearfusion]

Hi everyone,

Does anybody know the caliper piston diameters for the various E34 brakesets? The rotor information is commonly available, but I haven't found the piston diameters yet, although I have had a pretty careful look. It's not in the ETK and pretty well any online search I've tried seems semi-useless.

Thanks!

Fusion

[BillionPa]

all the single caliper front brakes should be the same, 60mm.

the rear is 40mm for vented disks and 38mm for solid.

[nuclearfusion]

Interesting about the front calipers - can anyone confirm the 60mm diameter on pistons for both the 22mm and 28mm thick rotors?

I only ask because given the +2 mm piston diameter for the 20mm thick ventilated rear rotors it would seem the pistons for the 28mm front rotors would have been upgraded similarly. (unless of course it was an attempt to push the common E34 brake bias slightly towards the rear in the 540i and M5 models?)

As for the rears, 40mm vs. 38mm pistons would yield approx. (40^2)/(38^2) = 1.108, approx. +11% braking power on the 20mm ventilated (540i and M5) brakeset compared to that of the other E34 models.

This, coupled with the much greater heat dissipation of the 20mm ventilated rear rotors could explain the significant difference in initial bite and also sustained braking felt by those upgrading their rear brakes. (I did this on my E28 533i and found a notable difference in brake performance when upgrading the fronts to E32, and again when upgrading the rears to E34 540i parts.)

Enjoy!

Fusion

[BigKriss]

Yes, The e34 535i and 540i use the same caliper pistons at the front.

Interesting about the front calipers - can anyone confirm the 60mm diameter on pistons for both the 22mm and 28mm thick rotors?