Thursday, May 12, 2011

Back On the Road?

Yesterday evening, I used a very sharp knife followed by a very fine abrasive pad to clean the glue out of the opening for the fluid reservoir until it was smooth and the old O-ring (yes, I know that it is supposed to be replaced every time the reservoir is removed) should seal just fine. I also ran the pad up and down the bore and got a really fine crosshatch pattern. Basically just cleaned things up really well. There was one place where you could tell that the rubber cup on the piston rests and this procedure removed that little ridge.  Cleaned up the master cylinder and piston with alcohol, lubricated the piston and O-ring with clean brake fluid and reassembled everything. Installed the master cylinder on the bike and poured in some brake fluid to check for leaks. None so far! Bled the air out of the system and the lever felt solid again. I used the lever to bleed the brakes as it works better than the hand vacuum pump so this meant that the piston got used a lot. At this point there was a tiny drop of fluid which looks like it may have came out of the piston end. Filled up the reservoir to the "Max" line. cleaned up everything, and put some clean paper towels under the master cylinder. This morning, no leaks so I went ahead and rode into work. I put down some rags on the fairing glove box to catch any leaks and now I'll just have to wait and see. At least it looks like I may be able to still get out and ride until the parts arrive. Gotta love the simplicity of these old bikes. I don't think I would be so willing to tear into anything current.


  1. Um- anything current? Dude at 52,000 miles the only thkng I tear into for the Bonneville is new oil and tires and one chain with sprockets every 42,000 miles. The rest of the time I ride! Happy fiddling!

  2. there is a certain feeling of sheer awesomeness when you can fix something by a thorough cleaning and careful assembly. God job!

    Enjoy riding!


  3. I tried to comment last night but blogger was down. Nice job getting the brakes to work. Hope you get some good rides in if your weather is good!

  4. Allen:
    You're right, it felt really good to get the master cylinder back together and have it not leak. One of the real joys of fixing old stuff like this Beemer.

    So far I've gotten in some good rides after work. This Sunday, the local loosely organized BMW group is having a ride. Hopefully it'll warm up a little. It has been barely above freezing this week.