To order these models for tandem applications, add a "T" to the end of the model number. The 3900-1 Series is also available in non-corrosive alloy bronze. Model 3900-S-B
For use with reverse manual lockout actuators on a single axle trailer. The kit includes: 2 ea. 3901-ST caliper assemblies, 2 ea. 3972-ST mounting brackets, 2 ea. 3971-ST rotors, and mounting hardware.
Model 3900-S-S
Includes the complete 3900-S-B kit plus an electrical solenoid to disengage the brakes while backing.
Model 3900-S-V
Null's patented "Free Backing Disc Brake System" for a single axle. The kit includes: 1 ea. 3901-ST brake assembly, 1 ea. 3972-ST mounting bracket, 1 ea. 3905-ST brake assembly, 1 ea. 3976-ST mounting bracket, 2 ea. 3971-ST rotor, 20 ft. of return line, and mounting hardware.
Model 3900-S-V-C
Same as model 3900-S-V to include two 3900-S-H Hub assemblies, bearings, studs, lug nuts and dust caps, two each 3002 flex lines, 20 feet of return line and mounting hardware.

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