Hydraulic System Junction Block: Description and Operation
JUNCTION BLOCKDESCRIPTION
A junction block is used on vehicles that are not equipped with Antilock Brakes (ABS). The junction block is located in front of the driver's side front tire behind the front fascia. The junction block mounts in the same location as the ABS Integrated Control Unit (ICU) does on vehicles with ABS.
It has six threaded ports to which the brake tubes connect. Two are for the brake tubes coming from the master cylinder. The remaining four ports are for the brake tubes going to each brake assembly. The valve is permanently mounted to a bracket which fastens to the engine cradle crossmember.
Later production junction blocks have the proportioning valves for the rear brakes mounted in them. One valve is mounted in each end. The proportioning valves are not serviced separately from the junction block. Vehicles with this type junction block no longer have proportioning valves mounted at the rear brake flex hoses.
OPERATION
The junction block distributes the brake fluid coming from the master cylinder primary and secondary ports to the four brake tubes leading to the brakes. Since the junction block mounts in the same location as the ABS Integrated Control Unit (ICU), it allows for the common use of brake tubes on the vehicle whether it is equipped with or without ABS.
Later applications of the junction block include two proportioning valves. Placed in the fluid flow passages leading to the rear brake tube ports, they balance front-to-rear braking.