1996 Plymouth Voyager break preportioning valve

The photo didn't show up, and it sure would be helpful. Trucks and minivans use a height-sensing proportioning valve in front of the left rear wheel. Problems with them are very uncommon. My daily driver is one of the last '88 Grand Caravans left in Wisconsin, the road salt capital of the world, and that valve has never leaked. The problem is, if it does, depending on where the leak is, each rear brake is on a different hydraulic system so you will lose brake fluid to one front wheel too, but you shouldn't lose brakes to all four wheels.

Check the level in the master cylinder reservoir. If it is empty, you might get some brakes by adding but you won't want to drive it any further than necessary, and certainly not where you might have to stop in a hurry. I've nursed my van through rush-hour traffic already, to get home, by using the parking brake, but that only works the rear brakes, and those only provide up to 20 percent of the normal stopping power. It is still not advisable to drive the van like that on purpose.

Proportioning valves are going to be a dealer-only item because there are so many variables that go into selecting one with the right pressure. If you get one from a salvage yard, you'll have the best chance of getting the right one if it comes from a van with the same year, wheel base, engine size, tire size, and weight distribution based on optional equipment like air conditioning and trailer towing package.

When you check the brake fluid level, look at the rubber bladder seal inside the cap. If that is blown up and mushy, the fluid has been contaminated with a petroleum product. That is a real expensive repair because every rubber part that contacts the fluid must be replaced and all the metal parts like the steel lines must be flushed and dried.

I was a suspension and alignment, and brake specialist at a Chrysler dealership from 1989 through most of 1999, then I taught Automotive Brakes for nine years, and I have never seen one of these fail. If only one part of it is leaking you still should have half of the brakes unless the master cylinder ran empty. The left rear and the right front are on one hydraulic system.

The brake fluid pushes on an internal spring-loaded piston. That piston moves when enough pressure is reached and it blocks the port to the wheel to prevent more pressure from getting through. There is no need to have a port or passage to atmospheric pressure, so what is probably leaking is a passage that had to be drilled from the outside, then the access hole was sealed. My guess is epoxy would seal it enough for a temporary fix of you can get it completely dried off, but under hard braking, you can develop over 2000 pounds of fluid pressure. I wouldn't trust any kind of repair other than to replace the assembly.