I have a low spongy brake pedal and don’t feel safe driving it. The pedal is way lower than normal. So I checked my brake fluid level and it is just under the MAX line. I have new brake pads and rotors on the vehicle from 2 months ago. I took it to the dealer and they said I need to have the HCU and Master Cylinder Replaced. They want over $1500 for the repairs. Do you think I should let them do it or is this something I could possibly do myself? Any thoughts would be appreciated.
Certainly this is something you may be able to tackle yourself at home. Many DIY’ers have been successful at taking care of there own brake problems for years. If you have the tools and some knowledge of working on brakes it should be an easy repair. That being said I have added the repair procedure below for reference along with a video i made showing how to replace the master cylinder. In the video I also explain a few things the auto repair manual doesn’t and more importantly I explain a work around. As there may be a possible way for you to correct this common problem of a low brake pedal without replacing anything or spending a dime. Watch it till the end to discover the quick fix and please subscribe, its free.
Replace Master Cylinder
Refer to Fig. 1 for exploded view of master cylinder components.
- Remove air cleaner.
- Remove battery and battery tray.
- Disconnect brake booster check valve from booster to deplete residual vacuum in brake booster.
- Then Disconnect brake fluid level switch electrical connector.
- Disconnect master cylinder brake tube fittings, plug brake tubes and brake master cylinder ports.
- Remove master cylinder mounting nuts, then master cylinder.
- Reverse procedure to install, note following:
a. Torque master cylinder nuts to 18 ft. lbs.
b. Torque master cylinder brake line to 21 ft. lbs.
c. Bleed brake system as outlined in “Brake System Bleed.”
BRAKE SYSTEM BLEED
PRESSURE BLEEDING
- Clean all dirt from master cylinder reservoir cap area, remove cap and top up brake fluid.
- Install bleeder adapter into master cylinder.
- Bleed longest line first.
- Attach rubber hose to righthand rear brake bleeder and submerge free end in container partially filled with clean brake fluid.
- Open valve on bleeder tank, apply 30-50 psi to brake system.
- Open bleeder screw and leave open until bubble free brake fluid comes from bleeder, then close bleeder.
- Continue bleeding brake system going from lefthand rear to righthand front and ending with lefthand front.
- Close bleeder tank valve. Remove adapter, fill master cylinder reservoir to proper level and reinstall reservoir cap.
MANUAL BLEEDING
- Fill master cylinder with suitable brake fluid.
- Attach a rubber hose to rear bleeder screw and submerge free end in a container partially filled with suitable brake fluid.
- Have an assistant pump brake pedal ten times and hold pressure on pedal.
- Loosen bleeder screw until fluid flow stops. Maintain pressure on brake pedal and tighten brake bleeder screw.
- Repeat until bubble free fluid flows from system.
- Repeat procedure for lefthand rear caliper, righthand front caliper and finally lefthand front caliper.
- Fill master cylinder reservoir to proper level.
- If required, bleed master cylinder.
HYDRAULIC CONTROL UNIT (HCU)
Bleeding the HCU is only required when removing or installing the HCU or master cylinder, or when opening the lines to the HCU. Carrying out the system bleed function drives trapped air from the HCU. Subsequent bleeding removes air from the brake hydraulic system through the bleeder screws.
- Connect a suitably programmed diagnostic scan tool.
- Access “System Bleed Function.” Go to “Tool Tab Chassis Braking ABS Service Bleed” and follow directions on scan tool.
- Manually bleed brake hydraulic system.
- Repeat procedure carrying out a total of two diagnostic tool cycles and two manual bleed cycles.
HCU, Depressurization
Mark the level of brake fluid in the master cylinder before starting the depressurization of the system. When the brake fluid level has increased approximately .47 inch, the system has fully depressurized.
Turn the ignition switch to the OFF position and let the vehicle stand at lest four minutes without opening the doors, pressing the brake pedal, or activating the key fob. If any of these actions occur, the system pressurizes and the procedure must be repeated.