MGB master cylinder(s) - started

Continuing on the MGB project, today is all about the removal of the master cylinders. This is the logical continuation of the prior post about MGB brakes where I did all four corners and the rubber lines but I was unable to successfully bleed the rear brakes.

How Works MGB Brakes

pic swiped from MGB forum

I briefly touched on this in the MGB brakes job posting (See: MGB Brake Job). The brake hydraulic system is very simple. From the pedal under your foot, a level presses against the vacuum-assist brake booster which activates the brake master cylinder. That's typical of any modern car. The MGB master cylinder is split into 2 halves, the front and the rear, with a rod connecting them so that when you press on the pedal and the brake booster activates the master cylinder, fluid is pressed out of two chambers. The chambers correspond to either the front or rear. This is a protection in case there is a failure in your brake system, keeping the other system intact so you can stop. Safety Fast!

Bleed Fail
This brings us to our brake problem, I did the four corners, and bled the front system. The rear system, though, would not bleed. First, the air bubbles would not stop and finally, the fluid stopped passing through. I thought I had fouled the rubber line install so I removed it and still couldn't get fluid. Rules out rubber line. Then I put it all back together again, and went to the master cylinder end. I disconnected the one hard line that ran to the back of the car and it could hold vacuum. So, the hard line is good. The master cylinder must have failed.

Master Cylinder
Again, the internet has opinions when it comes to brakes. Okay, pretty much that's true when it comes to anything, but in this case, there's a strong urging from the MGB community to replace the clutch master cylinder when you replace the brake master cylinder. That's because they stack-up against one another and removing just the master cylinder for the brake requires so much disassembly, it's one of those jobs you only really want to do once. There is even a reported odd circumstance where both master cylinders fail around the same time, so even if you avoid doing both, you find yourself replacing the other one within 6 months. I mentioned the rust/patina condition of this little car in my part 2 posting (See: Little British Car (Part 2)) about buying it. The patina on the brake booster was pretty bad, and the pedal box looked pretty bad. There were leaves, and other filth all up in there too. So, I decided that I'd pull all of it out, clean it up and paint what I could. That may have been just one sentence, but many weeks of effort.

Pedal Box

swiped from britishv8.org

The brake and clutch pedals attach to the car in a combined steel box that is attached to the inside of the engine compartment. There is a rectangular hole through which the pedals pass into the driver foot-well. Once the hydraulics are disconnected, the pedals are removed as a unit, still attached to the box. Once removed from the car, I disassembled the pedals, cleaned, sanded, wiped down, etched, primed, re-sanded, re-wiped and painted them (black). I did the same to the pedal box.

I have ordered and since received the brake and clutch master cylinders. I have not installed them yet, though, as other projects have jumped in front of this. The posts on these other projects will keep coming, and as they complete, re-assembly will start, and then I'll come back to the master cylinders. The picture on the right here from britishv8.org is very much what I am aiming for. I've bookmarked this guy's project page for inspiration. Very nice build.

As always, thanks for following along, and I'll post more soon-