How To Fix a Leak from the Brake Master Cylinder

Over the years, the brake master cylinder in your vehicle may start to leak.  This is probably due to the wear and tear during its long service period.  What happens is that the valves that are found in the interior of the cylinder begin to leak due to constant pressure.  Most people tend to replace the whole cylinder instead of repairing it thinking that leaks are tough to seal.  For those that want to save a few bucks, you will be surprised to know that you can seal the leaks yourself with a simple kit for a brake master cylinder which you can purchase in most car parts supply shops.  Here are some steps to get the job done.  These will involve removing the brake master cylinder, sealing it, and reinstalling it.

  1. Locate the brake master cylinder.  The first step will entail finding the brake master cylinder in your car.  Kill the engine of your car and pop the hood.  On the driver side at the back of your car’s engine, you will notice that there is a round cylinder around with a 12 inch circumference.  That is called the brake booster cylinder.  Mounted on top of it will be the brake master cylinder. 
  2. Remove the brake master cylinder.  Now that you have located the part, get a couple of wrenches and use these to remove the brake cables connected to it.  Loosen the nuts fastening the lines on the cylinder with the wrenches.  Be careful not to damage the brake cables since you will want to connect these once you install the repaired brake master cylinder later on.  Once the nuts are loose, place some rags under the brake master cylinder.  This will absorb the brake fluid that will be trickling from the lines and the cylinder.  Once that is done, locate the two bolts attaching the brake master cylinder to the engine.  Use a wrench to loosen the bolts.  When this is done, remove the bolts and take the brake master cylinder out from the engine.  Place it on a clean cloth on a table or work bench.
  3. Disassemble the cylinder.  Drain the excess brake fluid from the cylinder specifically found in the reservoir unit.  Once that is drained, use a screwdriver to remove the unit.  From there, you see a lock ring that is holding the pistons in place.  This is at the backside of the assembly.  Use snap ring pliers to remove the lock.  When this is done, take off the retaining ring that holds the valve.  You will see this where the reservoir unit is typically mounted on.  From here, all you need to do is take the pistons and valves out of the main body.  This can be achieved by lightly tapping the cylinder assembly.  The parts should slide out easily.
  4. Replace the parts with that of the brake master cylinder kit.  Once all the small and moving parts inside the cylinder is out, break open the cylinder kit you purchased and replace all the old parts with new ones.  Reinstall all the parts back the same way you removed them.  Remember to lock them all into place with the rings, both retaining and lock.  Once that is done, mount the reservoir unit and test if all the leaks have been plugged.

If the tests are satisfactory, reinstall the brake master cylinder in your vehicle, connect the brake lines and give it a whirl.  You will need to bleed it to check if the repairs you did worked.  Check the car instruction manual on how to bleed the brakes.


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