In Line of the lack of accurate information regarding the difference on ATE and Brembo calipers made for the R65, I decided to make my own informative thread about the difference between the two manufacturers.
Before I anything else, I would like to point out that these information on pertain to the Calipers found on Dual shock R65 only. Monoshock R65's use a different caliper as well as other models(R100 etc...) interchangeability between these calipers are unknown.
The Shell:
The Caliper Shells are very different in outer design yet very similar in regard to internal function.
*Different outer design
*Different Cutaway near piston(for piston shroud)
*The o-ring that seals the the two halves are the same
*Piston Seals are the same
(ATE Shell on Top, Brembo Shell bottom)


Piston:
The piston between the two calipers are almost the same, except for the metallurgy used by the two brands. ATE uses a chrome coating that tends to rust off while Brembo uses a more superior metal that does not rust and is of the color grey.
*Piston Diameter between two manufacturers are the same(36mm)
*ATE Pistons are taller by a little below 1mm
(Brembo Piston Left, ATE Piston Right)



Piston Shroud:
ATE uses a metal ring to secure the Piston shroud into the Caliper, unfortunately, the metal ring is a good possible source of rust that will eventually destroy the brake pads, causing break squeal and slowly kill the pistons without regular maintenance.
Brembo on the other hand, does not use any clamps or retainers at all.
The Brembo Piston Shroud has a lip that secures itself to the Caliper Shell.
*Brembo Shrouds have a larger outer Diameter

ATE on Left, Brembo on Right

Brembo Top, ATE bottom
Brake Pads:
Both brake pads have the same contact surface area. Different top portions to accommodate the different spring setups between the two calipers.
(Brembo Left, ATE on Right)


*As far as I can certainly tell, A Caliper piston from a dual piston Brembo Caliper taken from an R100 is larger (Diameter = 38mm) as well as the piston shroud inner diameter.
Comments as corrections are welcome.
