First Guess: This varies by year or perhaps by series.Hello,
After hours of looking around i can't find a thread that list all the sizes of the various brake components of JB style brakes. Please let me know if what i have so far is correct. I'm sure i have things wrong as all info is coming from other threads.
JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder
JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"
JB7(8400lbs)Single rear wheel:
1.25" Bore MC(used in JB5 and JB6 Hydro Units)
Conventional Calipers 3.15" Piston
Front Disc- 12.50x1.54
Rear Drum- 13.00x2.50
Vacuum- Double Diaphram(same as JB6)
1 1/16 rear wheel cylinder
JB8(10000lbs)
1.312" Bore MC
Conventional Calipers 3.4" piston
Front Disc- 12.50x1.54
Read Drum- 13.00x3.50
Hydraulic Hydro Boost
1 3/16 rear wheel cylinder
My '97 K2500 has JD7. JD7 in '97 uses hydroboost. According to my '97 service manual (Bishko, on DVD)
JB5 = vacuum
JD5 = Hydraulic
JB6 = Vacuum
JD6 = Hydraulic
JB7 = Vacuum
JD7 = Hydraulic
JB8 (single wheel) = Hydraulic
JB8 (dual wheel) = Hydraulic
JF9 = Hydraulic
All of the xx5 and xx6 use 11.57 x 1.25 rotors in front.
xx5 uses leading/trailing drums
xx6 uses 11.15 x 2.75 Duo-Servo drums
xx7 and xx8 use 12.5 x 1.26 rotors except JB8 (Dual wheel) that has 12.5 x 1.5 rotors
xx7 has 13 x 2.5 rear drums
xx8 has 13 x 3.5 rear drums
JF9 has 13.86 x 1.435 front rotors and 13.58 x 1.435 rear rotors
My chart doesn't show master or wheel cylinder bore sizes, or whether they're standard- or quick-take-up calipers.
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