A Few Common Brake System Problems
The most common brake system problem is failure of the master cylinder.
When this happens, the brake pedal can slowly go all the way to the floor when sustained pressure is applied. The brake failure warning light will usually illuminate or flash intermittently. It’s possible for this condition to exist without any loss of fluid. You should immediately repair this condition as brake performance is significantly reduced and unsafe. If you are going through fluid, (which is a serious problem that should be fixed immediately) there has to be a leak somewhere in the system.
Areas prone to leaking, in order of likelihood, include the master cylinder (usually leaks back into the brake booster so you may not see a sign of leaking fluid), brake line distribution block, calipers and brake lines.
Volvo pioneered the use of dual-circuit brake systems in the late 60’s, a major safety advance compared to single-circuit systems that leave you without brakes if a single line fails. Volvo also incorporated another innovative safety feature known as the “brake failure” warning. This relatively simple system warns you when the brake system 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. 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 completing an electrical circuit to illuminate 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.
The most common problem with the brake line junction block is intermittent leaking of brake fluid through the contact switch. It can be tough to diagnose as the leakage is very inconsistent. Replacing the block should be left to a pro or an experienced do-it-yourselfer, as there are eight 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 repair. Also, the brake system will require a complete bleeding.