Experience with DOT 5 (Silicone) Brake Fluid

Do any of you have personal experience with DOT 5 brake fluid in Beemers? If so, I’d appreciate hearing from you, as to whether it was good or bad.  In the meantime, I’ll share mine with you.

My bike is a 1974 R90/6, purchased in December 1976 with 5k on the odometer.  It has a single-caliper front disc brake.  Removal of the fuel tank to top-up the brake fluid four months later revealed a jet-black liquid in the brake system, which I flushed out with clean DOT 3. Occasional checks thereafter revealed that the fluid in the reservoir remained clean and clear, and there were no leaks in the system.  By  1981 (31k), the fluid in the reservoir was starting to look like Sierra Nevada pale ale, so I flushed the system again with DOT 3.

In 1982, having had good luck with silicone (DOT 5) brake fluid in a 1971 MGB and a 1966 Buick for about three years, I decided to try it in my bike.  Advice to the contrary notwithstanding, I disassembled the master cylinder and front caliper, found the pistons and cavities clean and bright – no rust or corrosion – wiped out all the old fluid with a clean rag, washed loose parts with soap and water, reassembled using the original seals, and filled the system with DOT 5.  There had been a very slight seep between the master cylinder and the reservoir, but decided that it wasn’t bad enough to go to the trouble of removing the reservoir.

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Changing Brake Fluid

Fellow militant Airheads, As far as general maintenance goes how often do ya’ll change your brake fluid?

The correct answer to this can vary with the amount of humidity in your local air. The manual says do it once a year. You change the brake fluid because it absorbs water from the air. As it does so it gets darker, also its boiling point goes down. This water can eventually damage parts. As I write this I have this vision of someone with a low level of anal retention insisting on using the most exotic oil but not changing the fluid because it’s not yuppie. These are the folks whose Airheads retire early as being too expensive to fix.

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Brake Fluid Maintenance

Copyright © 1999 by Oak Okleshen. Used with permission. All Rights Reserved. May not be distributed in any form without prior written permission from the author.

Most of the technical inquiries sent to my mailbox from airhead members relate to problems why their machine won’t go, or go properly, or may relate to a desire to make them go faster. Inquiries why they may not stop or questions related to brake and safety maintenance are woefully sparse. And in reviewing the technical index I put together for AIRTECH material published in the past, I find very little on the subject of brake fluid maintenance. Thus the question arises–is it really that important or is the subject embellished with a sales pitch for brake fluid and service at your local dealer?? Before you jump to any conclusions, let me cite a very real incident where I had a direct participation in brake system maintenance.

Locally, (not an airhead member…) a gentleman acquaintance called me late in the year (several years ago…) and asked if I would help him get his 1982 R100RT in running order. He stated the machine was not ridden in over 2 years and was in storage in his aircraft hangar. The battery was dead, and the windshield cracked as something had fallen on it. So he requested generic repairs and a full 10,000 mile maintenance schedule to be performed. I wasn’t fond of working on it just then but he insisted and not running at the time, trailered it out for work. I knew the machine well, as it had been in pristine condition prior to his ownership when purchased from another acquaintance locally…

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