Sienna hydrolic brake part

  1. What is the name and function of the junction box between the master cylinder and the brake lines to the wheels? This part has 2 input lines from the master cylinder and 4 output lines which go to the wheels.

    2. That box seems to have a clog to one of the output lines or it needs to be bled. The front brakes work ( a. car stops fairly well and does not pull, b. there is hydrolic fluid at the front left caliper bleeder valve). Fluid is pumped to left rear brake cylinder. No fluid is pumped to rt rear. When disconnected from the junction box, no fluid is found coming from the box (either when 1st disconnected or when brakes are pumped. There is fluid going to the front left when line is disconnected from the junction box and after reconnecting at the left front caliper bleeder.

    I hope to bleed the juction box by screwing in an adapter into the female that the left rear brake line goes into and forcing fluid up into the junction box.

    Is that a reasonable plan? Would doing that cause problems?


The “junction block” you are talking about is really a proportioning valve. It has internal, spring loaded valves that limit pressure to the rear brakes to prevent them from locking up. It has little effect on bleeding the brakes. It usually has an electrical connection, a single wire which activates the “Brakes” warning light on your dash…

One of the four outputs is not working.

Can the proportioning valve be rebuilt?

Can it be bled? There is an allen bolt on the front of it (and perhaps 1-2 other items that might be removable)

I hope to force fluid back through it to free up a stuck valve or remove some blockage. Have not figured out how yet