GM Service Manual Online
For 1990-2009 cars only

Brake System Specifications for Chevrolet Chevy P42 Commercial Chassis 1998

System

Master Cylinder Diameter

Front Disc Brakes

Rear Drum Brakes

Rear Disc Brakes

Brake Assist

JB7

31.8 mm

319 x 39.3 mm

331.5 x 63.8 mm

--

Hydraulic Hydro-Boost

1.25 in

12.50 x 1.54 in

13.00 x 2.50 in

--

JB8

31.8 mm

319 x 39.3 mm

331.5 x 63.8 mm

--

Hydraulic Hydro-Boost

1.25 in

12.50 x 1.54 in

13.00 x 2.50 in

--

JF9

40.0 mm

357 x 36.7 mm

--

346.8 x 36.7 mm

Hydraulic Hydro-Boost

1.57 in

14.00 x 1.44 in

--

13.60 x 1.44 in