Master Brake Cylinder

PROJECT 51: Master brake cylinder. To be filed under "Hope springs eternal," shortly after I bought the MG, back in late October of last year, I added a "Master Cylinder Rebuild Kit" to my Christmas list (along with many other MG items), and Santa didn't disappoint me.

The master cylinder is the small hydraulic pump that is connected to the brake pedal that forces the brake fluid through all of the steel lines out to the wheel cylinders to expand the brake shoes against the drums to make the car stop … so it's kind of important that it works right.

I finally got around to cleaning and disassembling the master cylinder assembly, and based on what I've learned about the REAL condition of the car since those early optimistic (blissfully naïve) days, I wasn't the least bit surprised to find that Santa had wasted the precious room in his sleigh on THAT gift.

My first clue that something might be wrong was when I had to extract the pushrod with a pair of Vice Grips. That part should normally just fall out when its rubber dust boot is removed. The rusty brake fluid that ran out when I removed the piston pretty much told me the rest of the story.

Although not as bad as I thought it would be, the cylinder bore had several spots of deep rust pitting.

When the brake pedal is pressed and the rubber piston seal passes over one of those pitted areas, the brake fluid leaks behind the seal, rather than getting pumped out to the brakes, causing a "soft pedal." That's if you're lucky. If the pitting and leakage is bad enough, the pedal goes right to the floor, and your life begins to flash in front of your eyes. (Been there; seen that; changed underwear!)

A complete new master cylinder is on its way. There will still be plenty of other things for Santa to bring me later on.

Master cylinder still in car.

Rusty brake fluid is not a good sign!

Brown crescents inside bore are rust pits.

On its way, now. Can't wait for Santa.