Replacing a Master Cylinder

In November of 2005, Lis started noticing a steady decrease in her ability to stop her 1969 Beetle. Before it got too bad, we did some poking around and found that the car's master cylinder was leaking brake goo all over. Time for a new one!

Here's a shot of the car either:
  1. rounding a corner much too quickly,
  2. performing its two-wheel balancing act at the circus, or
  3. jacked up in preparation to be worked on.
I'll let you guess which is the case.

There it is, the master cylinder in all of its glory. In this shot you can see all of the important bits and pieces attached to it - the two black cloth-covered feeder tubes coming down from the reservoir, the three metal-tube brake lines (the front-right on top, the front-left in the middle, and one for the back two on the right), and the wires connected to the two brake light switches. You can also see the puddle of brake goo on the pan below it. Notice how all of the connections on the cylinder itself are dry, but the place where it bolts on to the body is covered in goo. I suspect that's where the leak was.

Here, by the way, is where the wild master cylinder (cylindrius massafius) lives: just inside of the shadowy area in the middle of this picture. It's a rather cramped apartment, shared by the gas tank upstairs, the tie rods in the front room, and the front axle beneath the front porch.

Getting the cylinder out is a pretty easy job, at least in theory. All you have to do is disconnect all of the bits on the front part, and then locate the two bolts beneath the gas pedal inside the car. Here's what the holes left by those two bolts look like (I didn't manage to take a picture of them in the holes). The space is cramped, so be sure to use a box end wrench to do this. I tried a socket wrench the first time and ended up with a half-out bolt holding the wrench tight against the gas pedal.

Your particular car may or may not come with a mud dauber wasp nest in it. I hear that feature was pretty rare for this year.

Of course, theory and practice can never work out their differences and play nicely together. In this case, the nut holding in the front-right brake line was frozen up. Given the small area I had to work in, I couldn't see that I had rounded off the corners of the nut until it was too late. In the end I had to use the vice grips to get a good hard hold on it and give it a solid twist before it would budge. After that I was able to hobble along well enough with a wrench on the non-rounded corners to get it off.

Finally it came out! Here you can see how all of the parts are stuck together. The rubber boot on the right-hand side sticks through into the hole in the passenger compartment while the rest of the cylinder sits as you saw a few pictures back. Despite having the name Master Cylinder, this part ended up being disappointingly small.

From this angle you can see the hole in the rubber boot that accepts the poking rod from the brake pedal. The rod goes through that hole so that when you stomp on the brake pedal the rod gets shoved into the cylinder, compressing all of the parts inside. That boot was full of brake goo when we pulled it out of the car, leading me to believe the leak was in the seals on the piston inside the cylinder.

Here's the new part, complete with little green plugs in each of its holes. Note that it didn't come with new stop-light switches or a rubber boot. I had to carefully pull those off of the old one, clean them up, and install them on the new one. Don't rip that boot apart pulling it off!

This is what the end of the cylinder that is normally covered by the boot looks like. The outter casing appears to be cast iron, so everything inside had to be put in through this end. After it was all shoved in, that little circular washer-like thing was put in place to keep it from flying out again. I resisted the urge to squeeze the ends together to see what happens.

These are the parts I had to strip off the old cylinder to use again on the new one. They were covered in brake goo, and the contacts on the two switches were pretty nasty. I spent a while cleaning them all up some so they could last just as long on this cylinder as they had on the previous one.

After cleaning, I put the old parts on the new cylinder. Here you can compare the new verses the old. I made Lis promise not to get the new one as dirty as she had let the old one get. At this point the new one was ready to go in.

I couldn't put it in without taking one more shot of its clean glory. That is one good-looking master cylinder!

Remember that hole that the rubber boot pokes through? Here's what it looks like before you put the cylinder back. Note that the replacement procedure is easiest of you have four hands, two of which must be on very long arms: you need one hand to hold the cylinder in its place beneath the gas tank, one to guide the brake rod into its hole, one to unscrunch the rubber boot while guiding it, and one to balance yourself to keep the car from tipping over. Optionally, you could use two different people. I opted for the first method (with only two arms) and it took a lot longer than it probably would with two people. Note that you will need that same number of hands/people to get the bolts that go through the car body started.

For reference, this is what the Offical Volkswagen Service Manual would lead you to believe you will see instead of the above picture. Note how they cheated by removing most of the body of the car. Note also that they didn't even pretend to have not cheated - the guy's hand is resting where the body should be! The lesson? No matter what the picture looks like, it is going to be a lot harder in real life. Had the car actually looked like this picture, the whole procedure could have been done by one person in about an hour.

After putting the cylinder back in we just needed to reconnect all of the lines, hoses, and electrical cables like they were before. After filling the reservior with goo we pumped the brake pedal a few times and watched the goo squirt out of the line that hadn't gotten tightened well enough. After re-tightening that one we just had to bleed and adjust the brakes, and we were done! Since all of that happened in the dark during a rainstorm, I didn't manage to take any pictures. But here's a nice shot of the car propped up as I was getting ready to work on it. The concrete block was my stool.