If your proportioning valve is clogged, you may notice a decrease in braking power. This can cause a longer time for the brakes to respond when applied, or even make it difficult to stop the vehicle. Another symptom of a clogged proportioning valve is an uneven distribution of brake force on all four wheels. You may also hear strange noises coming from the wheels as they rotate while applying pressure on them with the brakes. Furthermore, if one wheel locks up sooner than others when applying pressure through the brakes, this could be another indication that your proportioning valve is clogged and needs to be serviced immediately by a qualified mechanic.