[A22-JAM]

Hi All,

So the end of last year I decided to start down the route of fitting the M sport brake set up to my car. Standard I have the Grey Brembos front and Bosch rear. I bought second hand Calipers to strip down get powder coated and rebuild. Now that I have them coated I came across the fact the rear calipers although looking identical have different sized pistons. I should of noticed when stripping them but didn't so stuck now. One is 40mm the same as the front pistons and the other 44mm as from what I'd read before purchase was the expected size of rear pistons.

Does anyone know if this is how they should be or if I'm missing something really obvious?

I'm going to look into buying a replacement caliper for the undersized one but this isn't something I came across when looking up about the calipers. I thought all M Sport calipers were identical. Has me questioning part numbers etc for making the purchase of another one.

Appreciate any help that can be offered

[Londoner]

Original Brakes on "high power" models (335i/340i etc)
Front rotor: 340mm brake rotor with 4 piston caliper
Rear rotor: 330mm brake rotor with 1 piston caliper

Original Brakes on "low power" models (320i/328i etc)
Front rotor: 312mm brake rotor with 1 piston caliper
Rear rotor: 300mm brake rotor with 1 piston caliper

M-Sport Brake Option (2NH) (Blue “M” calipers)
Front rotor: 370mm Brake Rotor with 4 pistons (for on "high power" models)
Front rotor: 340mm Brake Caliper with 4 pistons (for "low power" models)
Rear rotor: 345mm Brake Caliper with 2 pistons (on all models)

M-Performance Brake Kit (Yellow, Orange or Red “M” calipers)
For a "high power" car (all that have 4 piston front brake calipers as factory standard):
Sizes are the same as M-Sport 2NH option but all rotors are dimpled and slotted

For a "low power" car (all that have 1 piston front brake calipers as factory standard):
370mm front rotors, 345mm rear rotors - all dimpled and slotted

[R99]

It’s unclear from the ETK exactly when the change happened, but earlier cars had the smaller piston size. It was revised at some point to a 44.

This happens when eBay sellers buy random calipers from different cars to make up pairs to sell.

As you’ve seen, the caliper is stamped to show the piston size.

[A22-JAM]

Originally Posted by R99

It’s unclear from the ETK exactly when the change happened, but earlier cars had the smaller piston size. It was revised at some point to a 44.

This happens when eBay sellers buy random calipers from different cars to make up pairs to sell.

As you’ve seen, the caliper is stamped to show the piston size.

Thanks for this. Strange to find they changed it. Never noticed the piston size was stamped on it really helped with buying a replacement and knowing it was the right one.

[A22-JAM]

Originally Posted by Londoner

Original Brakes on "high power" models (335i/340i etc)
Front rotor: 340mm brake rotor with 4 piston caliper
Rear rotor: 330mm brake rotor with 1 piston caliper

Original Brakes on "low power" models (320i/328i etc)
Front rotor: 312mm brake rotor with 1 piston caliper
Rear rotor: 300mm brake rotor with 1 piston caliper

M-Sport Brake Option (2NH) (Blue “M” calipers)
Front rotor: 370mm Brake Rotor with 4 pistons (for on "high power" models)
Front rotor: 340mm Brake Caliper with 4 pistons (for "low power" models)
Rear rotor: 345mm Brake Caliper with 2 pistons (on all models)

M-Performance Brake Kit (Yellow, Orange or Red “M” calipers)
For a "high power" car (all that have 4 piston front brake calipers as factory standard):
Sizes are the same as M-Sport 2NH option but all rotors are dimpled and slotted

For a "low power" car (all that have 1 piston front brake calipers as factory standard):
370mm front rotors, 345mm rear rotors - all dimpled and slotted

This is also helpful info for when I buy the discs. thanks