Brakes

Improved ATE Braking

From the Airheads mailing list

I see a question and comments about improving front braking on a 1978 R80 from a single disk to dual. One person said go to brembo brakes.

It can be done, but prepare for a snowflake front wheel, the spoked one won’t fit with Brembos. Also you will need the later model down tubes as the attachment of the dampeners is by different means. So you just can’t replace the lowers. (But you can use the originals, if one can get some parts machined).

The wheel cylinders were of different sizes, there are some 38 MM units and some 40 mm units, the 40s give more brake power, the R75s and 80 had 38s. The R100 units and later (75 – 76) and R90S had 40s. So look at the cylinders, it is stamped on there some where. You can’t go by colors, some are silver, some black, the blue anodized ones were 40s probably they came on the 77-79RS.

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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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Broken front & rear brake light switches

This article is not concerned with the hydraulic pressure activated brake switches. Those switches, originally 34-31-1-233-959, were replaced with 61-31-1-244-334. You can probably substitute the switch used on old VW Beetles. Napa carries that switch as number SL143. There are other such switches: 3 terminal version is NAPA SL159, VW 113945515G; 2 terminal version is NAPA SL147, VW 0344004003.

This article IS concerned with the mechanically activated brake switches. All R series bikes FROM 1985 model year through 1988, & SOME 1989 Airheads were affected. ALL models of Airheads for those years!

BMW Service Information Bulletins were issued regarding the front & rear brake light switches, brake lever, etc. The bulletins applied to both Classic K bikes & to Airheads, but not exactly the same way. There were bulletins issued in 1987, updated in 1988 & a formal recall in 1989. Later bulletins were longer, with more details.

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Brake Fluid Maintenance

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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This long & extensive article covers both disc & drum brakes. There is a lot of information for 2-wheelers, some for sidecars & tugs. There is a complete discussion about brake fluids & bleeding. Much is applicable to any hydraulic brake system. Included is squealing information for motorcycles, especially Airheads, other bikes, Bulletins for K-75, Etc.

Warning: working on brakes is serious business. Read this entire article, perhaps more than once, before you begin work on your brakes. If you do not feel competent, take your bike to a qualified shop.

Broken cable or lever operated brake switch? (NOT the hydraulic switch). Brake pedal bolt not contacting the switch properly? (and it’s not a bent tube at the frame): http://bmwmotorcycletech.info/brakeswitches.htm

Regarding the hydraulic pressure activated brake switches: Those switches, originally 34-31-1-233-959, were replaced with 61-31-1-244-334. If you haven’t access to the BMW part, you can probably substitute the switch used on old VW Beetles. Napa carries that switch as number SL143.

FRONT DRUM BRAKES:

An article written by Duane Ausherman discusses assembly & adjustment of the 1955-1976 front drum brakes, with some applicability to the rear drum brake, & drum brakes after 1976: http://w6rec.com/

In my article that follows, below, I have numerous sections where I get into things Duane did not, regarding the drum brakes.

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