Brake Line Junction Block

Volvo pioneered the use of dual circuit brake systems in the late 60’s and it was a major safety advancement all other car manufacturers eventually adopted. Compared to a single-circuit system that leaves you without brakes if a single line fails, a dual circuit brake system provides at least 2 wheels with brakes in the event of a line failure. In 140 models Volvo added another innovative safety feature known as “Brake Failure” warning. This relatively simple system will warn you in advance that the brake master cylinder is having problems, is low on fluid or if there is a leak in the lines or calipers.

The system uses the dual circuit feature to monitor any pressure differences in the system that would indicate a problem. If there is a problem, a floating piston inside the brake line junction block (usually located low on the driver side frame rail in the engine compartment) will be displaced by the pressure difference. This allows a contact switch integrated into the brake line junction block to complete an electrical circuit illuminating the dash mounted warning lamp.

Any flicker or intermittent illumination of the “Brake Failure” lamp should be taken as seriously as a constant glowing lamp for safety reasons. Often repairing the problem will extinguish the lamp, but it may need to be reset in some cases. Refer to your shop manual for this simple procedure.

We have seen a sharp increase in failures of brake line junction blocks in the last couple of years. The most common problem is intermittent leaking of brake fluid. It can be tough to diagnose the problem, as the leakage is very inconsistent. Replacing the block should be left to a pro or an experienced do-it-yourselfer as there are 8 steel brake lines connected to it and it’s not much bigger than a D-cell battery so you can imagine how tight it is to work on. Also, the brake system will require a complete bleeding. Make sure and check your Volvo service manual for the correct sequence to bleed your braking system.