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Broken front & rear brake light
switches on BMW AIRHEAD Motorcycles.
(includes information on stiff throttles ONLY on 1985 K bikes

http://bmwmotorcycletech.info/brakeswitches.htm
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© Copyright, 2017, R. Fleischer

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.

Federal Recall Campaigns SEEM TO NEVER expire!....if your bike has a problem, BMW dealerships will fix it, if it is in the Recalled Group, for free.  

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BMW Motorcycle Brakes
(including conversions, upgrades, sidecar rigs, etc.)

© Copyright, 2014, R. Fleischer
http://bmwmotorcycletech.info/brakes.htm
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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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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.

1990 (45k):  Added brake fluid to top-up the reservoir.

1993 (48k): Bled brake.  Still seeping a little at the reservoir joint, but not bad.

1997 (52k):  The front brake was still working O.K. with no apparent leaks or sponginess of the brake lever, but the seepage at the reservoir/master-cylinder joint seemed to be a little worse, and removal of the reservoir revealed a flattened o-ring and some rust around the sealing surface.  Precautionary removal of the master cylinder piston revealed that all piston seals were still in “as-new” condition. However, there was rust in the bore near the entry hole from the reservoir, most likely caused by my failure to

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elbowBleederInstalled

Braided Stainless Brake Lines

When I purchased this RT the rubber brake lines were already almost twenty years old. There were no obvious signs of age such as cracking or leaks, but the brake lever was spongy, and even after flushing out the old fluid, wasn't as firm as it should be. Several kits are out there for replacement lines featuring teflon tubes covered by a stainless steel braid, which in turn is covered with a clear or colored plastic coating to prevent abrasion to adjacent components. They boiled down to two variations: The first kind were a one-to-one replacement for the BMW factory lines, and left the steel brake lines intact. The second kind used two identical lines that extended from the master cylinder on the handlebar to each caliper. I wasn't thrilled with the one-to-one kits as they left the hoop of steel brake line that connects the two wheel calipers intact. That hoop extends up and over the front wheel, then down to the calipers, and is infamous for trapping air when the brake system is opened. I didn't like the idea of a double long banjo bolt at the master cylinder either, but it was necessary if the second option of double brake line was used. I knew that "T" and "Y" hydraulic fittings were available, but was unable to find a kit that used one to provide the best option: A single line at the master cylinder going to a centrally mounted "T" and lines extending from there to each caliper. I'd been making brake lines for years, and figured it was just a matter of figuring out the proper fittings to make this one too.

After looking at the available options I settled on

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R100GS HPN Rear Brake Lever

I first ran across HPN's replacement rear brake lever while flipping pages in a Touratech catalog, and the idea of tucking the lever up out of the way seemed like a good one. The $140 price tag is very high, however, but when some insurance claim cash came my way I decided "what the heck" and ordered one (along with an oil cooler relocation kit).

 The kit comes with everything you'll need for installation except a drill. The instructions in the package are in German, however, and like the cooler, there is a help page for the brake lever on the Touratech USA web site (though it's not referenced from the catalog page like the cooler). I was able to piece together the path forward from looking at the illustrations on the German instruction sheet and reading the text on the Touratech web page.

The kit comes with three pieces: the replacement brake lever, a new cable stop for the rear drive end of the brake cable, and a cable alignment bracket for the pedal end of the cable. The latter is needed because the bend in the cable necessitated by the reversed lever makes the cable want to droop as it emerges from the brake pedal housing. The lever is aluminum, just like the original, and is the same length as well. It incorporates a jog so that the cable end will not hit the drive housing. The cable stops and brackets are cad plated steel, as are the mounting screws.

Installation consists of removing the original brake lever and installing both of the new cable ends. Begin by disconnecting the factory rear brake cable, spinning off the big wing nut and setting it aside in a safe place. Also remove the rubber boot from the cable. Pull the cable out of the stop in the final drive housing, and pull the cable out of the stop.

 Slide the HPN alignment bracket over the cable with the tail of the bracket pointing up and facing to the rear of the bike. With the brake pedal end of the cable fully seated into its stop, position the alignment bracket so that the end metal ferrule on the cable is at least 1/8" from the bracket. Mark the location of the hole in the other leg of the bracket onto the brake pedal housing. Remove the plastic cover from the housing and drill a 7/32 or AWG #3 hole in the housing. Using the provided bolt and nut, mount the bracket to the housing, again ensuring that the bracket is at least 1/8" back from the end of the cable ferrule.

Next pick the HPN cable stop out of the kit. It will re-angle the brake cable housing so it aligns with the new brake arm. It's not very intuitive how the new stop should be mounted, but the stop has a tab with a hole in it, through which the mounting bolt is inserted. The bolt then passes through the original anchor location of the cable on the drive housing.

Thread the cable through the stop and make sure the cable housing is bottomed in the new anchor. Slip the rubber boot over the cable.

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