How to Replace the Master Cylinder on a 1994 Buick LeSabre

The master cylinder is the hydraulic pump for your vehicle's braking system. The brake pedal is mechanically connected to the piston in the master cylinder. When you press the brake pedal, it pushes the piston forward and pressurizes the brake system. When changing out the master cylinder, you must bleed the entire brake system to remove air from the brake lines.


  1. Put on the safety glasses. Disconnect all brake lines from the master cylinder with the line wrench set. Remove the two bolts that secure the master cylinder in place with the socket and ratchet set. Place the master cylinder on the work bench.
  2. Remove the cotter pins securing the original brake fluid reservoir to the old master cylinder with the pliers. Remove the reservoir from the old master cylinder. Secure the new master cylinder in the vice and attach the reservoir. Bend the cotter pins with the pliers and fill the reservoir with brake fluid.
  3. Attach the plastic bleeder fittings (included with the new master cylinder) and clear rubber line. Direct the clear line back into the reservoir and keep it submerged in brake fluid. Pump the piston on the master cylinder slowly with the screwdriver and continue doing so. The master cylinder will be properly bled when there are no air bubbles in the fluid that is traveling through the clear lines. Hold the clear lines under the fluid and do not remove the bleeder attachments until you are installing that particular brake line.
  4. Mount the new master cylinder back into the vehicle and tighten the bolts with the socket and ratchet set. Attach the new brake lines one at a time and tighten them until snug with the line wrench set.
  5. Have a helper sit in the vehicle and pump the brakes. Bleed the rear brake assemblies and then the front. Replace any lost brake fluid after every wheel.