FAQ: Top Master Cylinder Questions

  • What type of fluid should I use: DOT 3, DOT 4, or DOT 5?

    As a rule, always use the brake fluid recommended by O.E. which is stamped on the master cylinder lid.

    Note: Always use new fluid from a sealed container.

  • What’s the difference between Dot 3, 4 and 5?

    Dot 3 and 4 are Glycol-based fluids and Dot 5 is a Silicone based fluid
  • Why does it take me a long time to bleed a step bore style master cylinder?

    Refer to the installation instruction sheet for special step bore bleeding process. Bench bleed first by slowly depressing brake piston then release slowly and waiting 20 seconds before you push again. NEVER pump piston/pedal with a step bore style master cylinder. Follow the same process on the vehicle.
  • Why does every master cylinder I install leak out the piston in the booster area?

    Make sure when bench bleeding that you use a blunt tool (wooded dowel) when bench bleeding. Check booster for a defective push rod seal. If this seal is bad, it could suck the brake fluid out of the master cylinder.
  • I replaced the master cylinder and now the pedal is high and hard, Why?

    The master cylinder is working correctly. Check for a faulty brake booster or frozen wheel cylinder/caliper.
  • The brake pedal is low and spongy. Is it a bad master cylinder?

    First, check for air in the system. Make sure master cylinder is level when bleeding. Air will compress in a hydraulic system causing a low pedal. Then check for brake hoses swelling/expanding under pressure. Then check brake drums/discs for proper specifications. And then check brake material.
  • Why won’t the right front brake release? I just replaced the master cylinder.

    The right front brake not releasing is either a problem with the caliper or brake hose. If the master cylinder was defective, most likely both front brakes would not release.
  • What causes the car to pull to one side during braking?

    Check the steering and suspension. Inspect both calipers for binding or sticky slides or pins. Check brake lining for oil/grease or uneven wear. Inspect brake hoses for restriction. Check for proper tire pressure.
  • What causes the brakes to lock up after only a couple of miles?

    Replace all brake fluid. Brake fluid is hygroscopic which means it absorbs moisture. Too much water in brake fluid will cause vapor lock and apply pressure to the wheels. Also check for proper push rod adjustments and stop light/cruise control switch adjustments.
  • Why is the piston stuck inside the bore of my master cylinder?

    Most likely, the fluid in the system is contaminated. The most common contamination is that petroleum-based fluid has been accidentally used in or added to the brake system. If that has happened it is almost certain that all rubber components in the brake system (hoses, seals, bladders) will need to be replaced after the system is completely and thoroughly flushed. If the contamination is due to moisture, rust and/or dirt, it might be possible to restore operation by flushing the system and replacing the brake fluid with fresh, clean fluid. Always use the brake fluid specified by the vehicle manufacturer. Always use fluid from a sealed container.
  • How can I test a master cylinder to see if it's bypassing?

    Simply plug the master cylinder ports and press the brake pedal. If the master cylinder is bypassing, the pedal will go down. If the pedal stops hard, the master cylinder is OK.

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