R32 GT-R Brake Master Cylinders

BM57 brake master cylinder. 1 1/16th inch bore. Rear line which goes to front calipers is split with block.

Brake master cylinders are probably the most sexy part of your entire braking system. Really. Honestly. Probably not.

When you press on the brake pedal, which is a type of lever, the other end actuates a rod that moves the piston in the master cylinder.  The R32 GT-R came with both BM44 (15/16th piston) and BM50 (1 inch piston), not sure exactly how those broke out.  However translating from Japanese, it seems like the three port BM44 was used on the Nismo, and possibly the N1, along with the GTS-t R32.  All the other R32 probably got the BM50 master cylinder at 1 inch.

The larger the diameter of the piston, the more fluid it moves. When you swap out to larger calipers, you want a larger piston in the master to be able to move more fluid down at each caliper.

Something we just were looking at, is the 2 and 3 port versions of the master cylinders. The BM44  is a 3 port used with non-ABS cars, and the BM50 being a 2 port used with ABS.

Brake Master Cylinder

• OEM Sumitomo R32 GT-R and GTS-t (Nismo and N1 maybe?)
• BM44
• Nabco 
• 3 port (No ABS)
• 15/16" piston  (23.8125 mm)
• 46010-02U20
• BM50 - Also OEM R32 GT-R and R32 GTS-t 4WD
• 1" piston (25.4 mm)
• Nabco
• 2 port (With ABS)
• 46010-05U20
• Rebuild kit
• 46011-52F26
• Alternate 46011-22P26
• OEM Brembo R32 GT-R Vspec/R33 
• BM57
• 1 1/16" piston  (26.9875 mm)
• 2 port
• 46010-05U02
• 46010-0V600 

ABS removed. Rear port, which controls the front calipers is tee'd off. This is a BM57 master cylinder

• R32 GTR (Non V-Spec, Nismo)
  BM50 master
  

  Master Cylinder diam (mm)	25.4 area 506.71mm²
  Front Caliper Piston(diam x qty)	40.4×4 = 5127.58mm²
  Front rotors (diam x thk)	296×32
  Rear Caliper Piston(diam x qty)	38.18×2 = 2289.78mm²
  Rear Rotors (diam x thk)	297×18
  Brake to master ratio	14.63

• R32 GTR V-Spec / R33 / 34 GTR with Brembos
  BM57 master
  

  Master Cylinder diam (mm)	26.9 mm 568.32mm²
  Front Caliper Piston(diam x qty)	(44+3Cool×2 ... leading pistons smaller then trailing 5309.29mm²
  Front rotors (diam x thk)	324×30
  Rear Caliper Piston(diam x qty)	40×2 2513.27mm² ratio FR = 2.1125
  Rear Rotors (diam x thk)	300×22
  Brake to master ratio	13.76