Brake Master Cylinder
A visual inspection of the entire hydraulic system should be performed to rule out any external leaks. Look at all the connections including the calipers and wheel cylinders. If the vehicle has no external leaks, suspect and inspect the master cylinder.
The master cylinder consists of two pistons that work in tandem to apply pressure to the braking system. These pistons use cup seals to seal fluid in the pressure chamber. As the
seal moves past the replenishing or "compensating" port it begins to create pressure in the pressure chamber, through the lines, and onto the braking units. A return spring forces the piston back to its resting position. This action allows the brake fluid to return from the brake lines and piston chamber into the reservoir. If the brake pedal is over adjusted or there is debris blocking the compensation port the fluid will not be able to return to the reservoir. This can result in residual and excess pressure in the braking system. This residual pressure can cause brake lock up. Loosening the flare nut at the master cylinder port will often relieve this excess pressure, but will not fix the underlying cause.
If the fluid bypasses the cupped seal on either the primary or secondary piston, the peddle will drift to the floor and you will have to continually pump the pedal to maintain pressure. This is a common problem with all types of vehicles. These seals can wear in time or become contaminated. The primary pistons cup seals are located on the peddle side of the master cylinder and the secondary facing the front of the vehicle. A piston cup seal is located at the rear of the primary piston to prevent fluid leaking into the brake booster.
