Page 6 – Airheads Beemer Club

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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Brakes

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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Rear Drive Ratios

Variables for the chart are your actual on-the-road tire diameters (modest effect); tire pressures/temperature (tiny effect). The variation in UNLOADED diameter of a 4.00-18 rear tire versus a 120-90×18 rear tire is about 15 mm in the WORST case I know of. However, the actual rolling circumference varies little (probably about 2%, but could be larger). Hence the values shown below are THEORETICALLY fairly accurate, and some are taken from a BMW chart dated 1978, others are calculated, and some are actual test data. Values are theoretical; and do NOT account for tire slippage and tire variations, nor for speedometer and tachometer variations. Because of these factors, rpm is LIKELY higher for a true speed as charted.

See notes at end of this article!! The speedometer ratio is printed on the dial of most speedometers. The author’s website discusses things in much more depth, and includes expanded ratios for earlier models, etc…..link at the end of this article.

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Driveshaft Bolts, the split lock-washers…..and, push-starting cautions

The four TRANSMISSION OUTPUT FLANGE BOLTS CHANGES;…split lock washers, updates, …and….pushstarting! © Copyright 2021, R. Fleischer https://bmwmotorcycletech.info/drvshftboltstoolstorque.htm 47 Background and History on these 10 mm 12 point bolts and lockwashers used at the transmission output flange: The earliest bolts for the /2 & the Airheads (transmission output flange-to-universal joints) had steel split-type lock-washers, & were […]

Throttle & Clutch Cables

In my shop I saw many control cable failures from these things.

1. Throttle cables on the Airheads: Left cable failing at the carburetor, due to the throttle cable being bent as owners checked the oil dipstick. Do not bend the throttle cable at the left carburetor when checking your oil. There is no need for the oil dipstick to be overly-tightened. Bending the left throttle cable is a prime cause for that left cable to have increased friction, possibly spread some coils on the wrapped sheath (& making that carburetor difficult to synchronize, if bad enough), & eventually you might break an inner strand …usually where you can see it between the throttle lever on the carburetor, & the sheath. A single strand found broken (You do inspect these cables regularly, don’t you?), will usually cause other strands to eventually break from the same reason why the first strand broke ….this will …or can …result in total cable failure in as little as few hundred miles or so.

2. The bushing at the clutch lever at the handlebars is a replaceable plastic part and as it wears the result is the lever can move up and down & also allow angular motion. If worn enough, the stranded core of the cable will start rubbing, or even catching, on the sharp edged guiding slot in the lever. Eventually a strand breaks, failure comes soon as more strands break. The bushings are easy to replace and not expensive. If your new bushing does not finger press into place, heat the lever first. The Nylon-like bushing is 32-72-1-232-662 and has been used from 1976 onwards. That bushing may need light reaming for a good fit to the pin. If you do not have a 8 mm tapered ream, you can use very carefully selected drill bits, to progressively remove a quite small amount of material, a few thousandths at a time …until the pin fits properly …an easy, but not loose, push-sliding fit. The lever has a recess, and in that recess must be a waverly washer, 32-72-1-230-871. I recommend the sharp edge of the slot in the clutch lever be filed smooth. Be sure the crimped end of the cable that fits into the clutch lever at the handlebars is not fouling the lever.

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Lubing Steering Head Bearings

Cleaning and lubrication of the steering head bearings should be done at a scheduled mileage/time but most let it go until the steering has a ‘notch’ felt in the straight ahead position. This procedure was developed specifically for a 1983/1984 R100RT, but is similar for all Airheads. I advise you to read this procedure through before beginning. Cleaning and regreasing MAY WELL eliminate “notchy-ness” that SEEMS to indicate need for new bearings and outer races. It is best, but not mandatory, to do this procedure after installing new balanced tires, as road crown and tire squaring wear, and balance, might have an adverse effect on trying to make final on-the-road adjustments. This is not hardly just for the front tire….most riders do not know that a squared-off REAR tire is THE most common cause of wobble and weaving from the tires. The author has usually, but not always, done this procedure to his own bikes after installation of a new front tire, but when the wheel is off the motorcycle. If your REAR tire is not squared-off considerably, it will be OK for the final procedure, which are riding tests to get the preload adjustment ‘just right’. It is possible to do this procedure with the front wheel in place, usually that means having the front wheel hanging over the edge of a curb, or the centerstand is in use and on a piece of wood, so the front end can be dropped a couple of inches.

Cleaning and lubrication of steering bearings is not at all difficult, but if a bearing is found truly bad, replacing them is more labor intensive, as part of any fairing must be removed, and possibly brake piping, cables, etc. Contrary to some popular belief, our BMW steering head bearings of the tapered ‘Timken’ style may well last over 200,000 miles. If the bearings/races/shells are in good condition and properly greased and adjusted, the steering will be light, smooth, without any straight ahead notch. You likely will not find out if the bearings are really bad, that is, in need of replacement, UNTIL you first try cleaning and greasing. In a SHOP situation, the bearings are not cleaned and lubricated and then adjusted to see if any notch is gone. In a SHOP situation, labor is too costly for that. A shop can not take the time to clean and regrease, and then find out that the bearings really are bad, so a shop always replaces a notchy bearing. YOU, on the other hand, don’t need to do that…..and will often save a LOT of money, and a considerable amount of labor saving is possible.

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