Brake Caliper Compatibility? Rear single vs dual piston.

[Brian Mullen]

I'm working on putting a Dana 80 rear-end into a small RV.  The disc brake conversion kit I'm planning to get uses JB7 brake calipers from GM Trucks.  My understanding is that all of the JB_ series calipers mount up the same, the only difference is the piston size.  Browsing Rock-auto.com I found something interesting though.  For a 2000 C3500HD there are the usual JB6 and JB7 options, but also a dual piston caliper.  Would this dual one also fit the stock JB_ mounting brackets?

Thanks.

[lazylaz]

They are not all the same. JB6 and JB7 are two totally different brake calipers, mounts, brackets and caliper pins, brake pads and mounting bolts. Also the rotor sizing and back spacing requirements changes from one to the other. The FIRST picture is a JB6 equipped rear axle caliper and mounting bracket. The 2nd picture is the difference in sizes between the 2. The top is JB7 and the bottom is JB6. The 3rd pic is the jb7 caliper mounting bracket and  mounting plate. Notice the size difference between the 2. The final pics are the pad size difference,  the piston size difference, the caliper size difference and the difference between the pins. You can do with one or other but not both and cannot mix and match them. The JB7 calipers use 2x2.5" pistons and  JB6 use 2x2.34" pistons. The other issue is rotor size. With a JB6 option code the rotor size can go as small as 280mm. The JB7 option a min. of 330 mm is required. The engineering data shows is the larger rotor has more rotating mass therefore more clamping force is required to slow down which results in the larger caliper and hardware. Also a 3mm rotor shim is required if a jb7 option is equipped on certain axles to prevent caliper binding at full travel. Hence the longer caliper guide bolts. The ABS pump is the same across both platforms on the 2500/3500 but the Power Booster and or Hydroboost system and master cylinder are sized differently between the JB6 and JB7 option codes and needs to match in order for the braking system to work correctly.