Restomod Racing

The removing of the air in the brake system of the Corolla GT-S proved to be a challenge.  As you may

know, bleeding brakes can be accomplished by several means.  There is the method of pressurizing the master cylinder or the method of using suction at the wheel cylinder and the more common method for use by backyard mechanics, the pumping of the brakes.   When Keith was trying to remove the air from the Corolla, he ended up using all three methods.  No matter which method he used, the brakes refused to work. 

It was theorized that the air was trapped somewhere in the system.  In order to bleed the brakes he had to first fix the calipers on both the front and rear of the passengers side.  The reason was that the bleeding nipples were sheared off on them (previous owner must have broken them off).  Once fixed he started by using the method of pressurizing the master cylinder.  He first used the Motive Products Power Bleeder.  You fill the container full of brake fluid and then it is pressurize it.  The new brake fluid is then pushed into the master cylinder and through the brake system.  The air is pushed out along with the old fluid through the wheel cylinder bleeding nipple.  He started by going to the furthest wheel and moving to the closet wheel to the master cylinder.  When this didn’t seem to work, he went to the method of sucking out the air and fluid through the wheel cylinder nipple.   You use a vacuum pump that draws the fluid air into a special cup make for bleeding brakes.  When this method again didn’t seem to work he used the common method of pumping the brake peddle 3 times, hold the peddle while the wheel cylinder nipple is opened to release the air and fluid into a cup.  Once the air and fluid stops coming out, the nipple is closed.  Once the nipple is closed the brake peddle is now released.  You can not release the peddle before the nipple is closed, otherwise air will be sucked in through the nipple when the peddle is released. 

After using the three methods and none appeared to work, it was time to go back to the drawing board.  The first thing was that the brake was working before the bleeding process.  So why would it not work now?  After some research we noticed that there was air bubbles coming from the master cylinder when ever we pumped the brakes.  We decided to bleed the master cylinder.  We first started by loosening the line at the master cylinder that goes to the rear wheels.  When we pushed the brake peddle to the floor, no fluid was noted to come out.  After doing this a few times we decided to move to the front brakes.  We tightened the line to the rear brakes and loosened the line to the front brakes.  We noticed that fluid immediately came out when the brake peddle was pushed to the floor. 

We decided that the master cylinder was the problem.  To make a long story short, after replacing the master cylinder all was good.  Now the problem was to determine why the master cylinder went bad when it was working before.  What we determined was that the master cylinder piston was ruined when the peddle was pushed beyond it’s normal travel (distance pushed when brakes were working normally). 

In other words, the system was old and neglected.  Due to the neglect, the master cylinder bore became lined with small particles such as rust.  As long as the brake peddle did not move more that its normal travel, all was fine because the bore was in the clean area.  When the brake fluid was leaked out and the peddle was pushed beyond its normal travel, the pistons rubber cup now moved into the area of the bore which normally was not touched by the piston.  This part of the bore is lined the particles due to the neglect and it acted as sand paper on the pistons rubber cup.  This chewed up the rubber cup and caused it to leak.  In our case only the rear piston was affected.  The front piston was fine.  Remember that the brake system must be kept up so that the master cylinder bores stays clean.  Do regular maintance by changing your brake fluid as directed by you manufacturer.