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Throttle & clutch cables. Clutch lever (at bars) bushing.
Confusing design changes to throttle cams & gears.
Speedometer cable rubber boot at transmission.
Speedometer & tachometer cables.
Control assembly perches/wedges.
© Copyright 2020, R. Fleischer
https://bmwmotorcycletech.info/controlcables.htm
7B & K30
INTRODUCTION ...and description and some fixes for problem areas:
In my shop I saw many control cable failures from these various things.
1. Throttle cables on the Airheads: Left cable failing at the left 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. Don't injure the cable when loosening the dipstick. Note also that there is no need for the oil dipstick to be overly-tightened. Bending the left throttle cable at the carburetor is a prime cause for that cable to have increased friction, possibly spread some coils on the wrapped sheath & making that carburetor difficult to synchronize, if the cable is bad enough. Eventually you may break an inner wire strand ...usually where you can see it between the throttle lever on the carburetor & the cable sheath. A single strand found broken (You do inspect these cables regularly, don't you?), will usually cause other strands to eventually (usually within a few hundred miles) break ...from the same reason why the first strand broke ...this will result in total cable failure.
2. The bushing at the clutch lever at the handlebars is a replaceable plastic sleeve. If worn, the lever could move up and down & also allow excessive angular motion. If worn enough, the stranded wires 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 an 8 mm tapered ream, you can use very carefully selected drill bits, to progressively remove a tiny 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 cable strands 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. Be sure the barrel can move smoothly at the clutch lever (tip) located at the rear of the transmission. Many transmission-mounted clutch levers require a bit of filing and sandpapering to allow the barrel to
rotate smoothly; the problem is that the curve for the cable barrel is very slightly too small ...this is an easy fix.
See: https://bmwmotorcycletech.info/clutch.htm
3. Poorly made cables, usually (but NOT always) aftermarket types. BMW cables are lined and last a long time, and are smooth-operating with little friction. Note that some poorly made BMW cables have been seen. The areas of poor cable manufacture are generally at the barrel & barrel tip area; especially at the handlebars end of the clutch cable, and some hand work will fix this. Check carefully how the handlebars clutch lever operates...the stranded steel inner cable must not foul the lever slot as you angularly move the lever, and the cable barrel must rotate smoothly in the lever. Pay attention to #2, above.
4. Failure to route a cable properly ...typically resulting in too-tight bends or insufficient flexibility. Do not tie the throttle cables down with wire-ties or wire-wraps where they were not supposed to be tied down. The clutch cable has only one tie-down, on the right frame tube. Do not miss-route cables, they must not have sharp bends.
5. Lubricating BMW cables ...lubrication attracts abrasive dirt and may swell the liner (a nylon-like material). Only the very earliest original-as-shipped /5 cables were not lined and can be lubricated. DO NOT OIL BMW CONTROL CABLES is a good practice.
6. On all motorcycles: ...failures occur from not ensuring that the cable end barrel's (both ends of the cables) can rotate smoothly. Hand file the barrel. Sometimes the crimped part at the end needs attention too, depending on style; this was especially so for the clutch cable, some were improperly made. Lubricate barrels with moly grease or moly-oil. This also applies after gunk/wash jobs; re-lube the barrels! I recommend lubricating the barrel ends at the carburetors after every bike washing. ...I like to let them dry at least overnight first. Failure to do this can lead to broken cables. BE SURE the cables can freely ROTATE in the fitment area.
A listing of control cables by part number, lengths, etc., is much further down in this article.
Why the complicated throttle assembly design? Cleaning and lubrication:
Occasionally I read or hear commentary about the complexity of the BMW throttle assembly. It requires cleaning & re-lubrication every few years, has synchronization marks on its cam gear & throttle sleeve; and, is slightly tricky to assemble (I get into that, later in this article), but easy once you know how (unfastening at the end away from the throttle, at the carbs, is one trick). Sometimes, if not mostly, the commentary is negative. This reflects on the commentator, who does not understand the design, which is superior to most motorcycle throttle control assemblies. The BMW design is quite good; this includes whether it is the single-top-cable type (preferred as the carburetor synchronization is better & longer-lasting), or the dual-cable type.
The throttle cam gear assembly was designed by BMW to be non-linear. As the throttle is initially rotated by your right hand from off to on, the cam design is such that the throttle cable initially moves a rather small amount per throttle rotation amount. As the throttle is rotated more & more, the cam moves the cable inner strands faster, in proportion, for any particular amount of throttle movement. The advantage is that as one takes off gently from a stop, there is smoother control over the carburetors; there is none of the jerky sensitivity of the throttle that one finds on many motorcycles, particularly some that are fuel injected.
BMW used different throttle cams for the various types of carburetors (primary difference is with 32 mm vs. 40 mm carbs) and for different sized engines. BMW also changed the design of the cam and cover in later production, and this is detailed in a section well below here.
An additional feature is that the design is such that the throttle cable is a straight-pull; there is no bending of the inner cable as in many other types of designs; thus the throttle cable at the bars-end can be expected to last a very long time, without excessive friction, nor fraying nor breakage. BMW even specified a Nylon-like lining material in the cables after the /5. Cable breakage at the throttle at the handlebars is almost totally unknown on BMW Airheads. It is the other end, at the carburetor, that will fray & break ...typically either because the rider does not keep the end barrel lubricated; and/or, bends the left throttle cable while checking the oil level dipstick.
The human hand is fastened to the human wrist & there are only so many degrees of easy movement in the average wrist before you'd have to release the throttle, and re-grip it further along. Therefore, there are restraints on the amount of throttle rotation per amount of cable movement. This is set by the throttle cam shape, & by the gear ratio between the cam & the throttle tube. BMW made a good compromise between this over-all 'throttle gear ratio', & the need for relatively good response for small throttle openings .....yet also allowing maximum throttle (100% carburetor opening) to be attained.
If you lubricate the throttle gears/chain assembly now & then, and the cable barrel ends quite regularly, and ensure they fit properly .....wear will be slow. Wear is almost entirely the teeth on the cam and teeth on the throttle. The teeth are usable until they get worn to a quite grumbly-feel point; or, overly pointed. Some moderate miles later they strip. There have been quite rare instances of a stripped throttle/cam, and a tooth breaks off and jams the throttle. So....be sure to keep the parts lubricated....and inspect them at lubrication time....riiiight ?
Throttle gears & cams, some specific problems:
There are ...or can be ...complications involved ...if you want to replace the throttle assembly gear-cam and/or assembly cover. They are not the same between early & late models. They are also not the same for 32 & 40 mm carburetor models. Some parts are no longer available, so you need to know which later parts are correct ones that will fit your bike. It is problematical with some dealership parts departments that you will get the correct items, so bring along the old parts. Know the details, see below, because just having the old parts along is not necessarily going to tell you ...nor the parts department ...everything you need to know, depending on your bike's throttle parts. There are even complications from installing different master cylinder piston sizes, for those MC that are mounted on the handlebars as part of the throttle assembly. A knowledgeable parts department person can be very helpful; often, this means a non-dealership repairs/service company, which we generically call Independents. The internet-located Airheads list, hosted by Micapeak.com, is a good source for information about Independents.....and I cannot overemphasize the need for these experts, for work, parts, ....and advice. More information is below.
The throttle assembly parts have caused confusion because BMW changed the design of some of the cams & the cam cover (especially for single throttle cable versions) in the twist-grip throttle assembly. Some earlier parts like the original cam gears are no longer available, so combinations of later ones must be used. I'll try to explain things in the next few paragraphs.
BMW's does not list the throttle assembly in the carburetion section of literature; rather, it is in BMW Section 32, which is steering.
The proper cover plate to use with the later throttle cam assembly is: 32-72-1-457-050.
The cover plate, 32-72-1-242-561, underside, was flatter at the screw hole.
The newer plate has a round protrusion at the center, and that is about 1/2" diameter & maybe 1/4" deep.
The throttle cover was 32-72-1-233-538 for the earliest models.
The new cams are thinner, don't fit the old assembly cover.
The cam assembly for the 40 mm carburetors is now 32-72-1-457-081.
The cam assembly for the 32 mm carburetors is now 32-72-1-457-080.
The throttle tube did not change.
The cam gear for the R65 series is 32-72-1-238-378.
Be sure what you purchase will fit. The throttle assembly has been a PIA, and it may be best for you to contact knowledgeable Airhead parts folks, such as Ted Porter's Beemershop or Tom Cutter's Rubber Chicken Racing Garage, or Anton (see box just below) if you don't understand.
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Anton Largiader did an excellent article on these above items: http://largiader.com/articles/throttles/ Anton also did a good article on control cables: You may find differences in part numbers and sizes between Anton's article & mine regarding cables;...my chart is way down this article you are reading. We did not necessarily measure the cables in the same way. |
Some folks have problems with unfastening ...and especially with re-assembly ...of the throttle cam/tube/chain/cable. You do not have to loosen anything at the carburetors nor the T connector under the tank (one cable models have those). You MAY want to unfasten the throttle cables at the carburetors, but I find that time-consuming, and wasteful of labor with synchronization, so I have shown you how I do it, below:
First, unscrew the single large slotted screw in the assembly cover. Lift off the cover plate. Notice that the throttle end of the cover plate has a curved and downwards section that sticks into a corresponding slot in the throttle tube. That keeps the throttle tube captive once the cover is in place.
Notice that the throttle tube has gear teeth at its inboard end and note the mark stamped into or next-to a tooth, and there is a corresponding stamped mark on the cam. When re-assembling, the marks must be lined-up to point to each other.
After you re-grease the cam, etc., and are ready to re-assemble, line up the two marks, throttle meshed to the cam teeth. Hold onto the throttle, pull on the cable(s) sheath(s) and hook the sheath(s) end(s) to the place provided for it (them), in such a way that it (they) is/are bottoming in the machined area. You will be pulling against a moderate spring tension. Do not let the cam slip, versus the throttle tube, you want the identifying mesh point marks to continue to line-up. With your left hand holding the cover, and right hand on the throttle, carefully push the cover into position. The cover will fit perfectly, no special force needed. Install the large head slotted screw reasonably tightly.
Some throttle assemblies have a friction screw, a large knurled shiny 'thumb-screw" operated by your finger tips, as a rider, you can use it if you wish, just use it carefully and wisely! Before you decide to use it, there is an article on this website about using throttle friction devices. If you use a minimum or modest amount of friction in the adjustment, so the throttle will return to off by itself, instead of staying at a higher than off setting (with hand off the throttle), then you probably will be OK. Read: https://bmwmotorcycletech.info/throttlescrews,etc.htm This was originally entitled something like Snowbum Gets Off & Running.
If you have the type of throttle on the bars with one cable coming out of it, you have (unless you are riding a BMW single!) a tubular junction, a T connector, under the tank. That has an adjustment for the single upper cable free play. Proper adjustment is to take out most, but not all, of the CABLE SHEATH free play. Do, also, rotate bars from left stop to right stop to be sure you still have some free play. I like a bit less than 1/8" of free play at the throttle sheath at the bars. Be sure the rubber sleeve on the nose of the T connector is in good waterproof condition. Failure to have the cable properly adjusted at the T connector can result in insufficient throttle movement for the carburetors; that is, you will not be able to get full throttle; or, if too tight, idle will never be stable. These bikes have a similar T connector for the choke (enrichener) cable. Neither T connector innards are normally to be lubricated. If yours is not perfectly smooth operating, you can disassemble them and clean the insides and then coat the piston with a dry lubricant like MolyKote M-88 or even graphite powder as used in locks. Dryslide sprays as used on bicycle chains can also be used ....just spray the tubing and piston, allow to dry a few moments, then assemble and adjust the free play.
In your on-bike tools & parts, you really should have a spare clutch cable, & a spare throttle cable(s). There are all sorts of lengths of cables, be sure you have the correct ones for your model, your carburetors, & your type of bars. BMW often prints the actual ordering cable number on the cables in white print.
Speedometer and Tachometer cables.
All speedometers. Mechanical tachometers.
If you have a jumping needle on either speedometer or mechanical tachometer, you can consider cleaning and lubrication by a specialist, but it is possibly better for you to do some of your own testing and analyze the problem first. You may be able to fix the problem yourself. The odometers have been known to act up. It is not uncommon to have the odometer be intermittent. Some models have ODOMETER gears...these are the outside gears...and there is a mesh adjustment to check and lightly grease them. Another common cause for an intermittent odometer is where the internal ODOMETER shaft (very small diameter, steel), fits into the plastic or metal first gear. Clean the interface, and put one tiny drop of Crazy Glue or any Loctite at that junction of shaft and gear. I use a toothpick to apply that TINY droplet. Think about what/why you are doing this, before you do this!
A well-worn drive cable can cause a lot of jumpy-ness, and can be tested, although rotating and feeling, cable disconnected top and bottom, is not always going to give a totally definitive test. One can test the speedometer/odometer by using an electric drill and making an adaptor from an old end piece of cable, or squaring a nail end. The drill motor should have a direction reversing switch and best to also have a speed control. You can force lubricate the cable with a decent lubricant. A graphite type works OK. There are cable lubrication devices, but most of you will likely just remove the cable, and let a decent liquid lubricant drip down the inner cable, drops at a time. Cable lubrication is a last resort 'temporary fix'; and may cause swelling of the plastic liner of the cable, depending on the product you use.
Otherwise it is time to overhaul the instrument and/or get a new cable.
Speedometer cable rubber boot at the transmission (this has caused a lot of $$$ damage to a lot of Airhead motorcycles):
The speedometer cable rubber boot located at the right rear of the transmission must be replaced if it is in poor condition. Failure to do so will result in water entering the transmission causing a very high repair bill. The top of this boot must fit tightly all-around the speedometer cable; it should NOT have a zip tie or wire tie on it, as that will likely squeeze the rubber out-of-round, letting water get inside.
Remove the 10 mm hex hollow bolt that holds the negative battery cable lug to the rear of the transmission where that hollow bolt also keeps the speedometer cable in place. The hollow bolt is also the breather for the driveshaft (& the transmission on most Airheads). The hollow bolt should have two flat washers, one under each side of the battery cable lug, & there should be a waverly type locking washer against the head of the bolt. You can modify the battery cable lug by snipping it just enough to be able to push it over the hollow bolt. This modification allows you to disconnect the battery without completely unscrewing the hollow bolt. You must have the washers, so that you will not spread the cut lug during during tightening. Never over-tighten the hollow bolt as it will fracture/break!
Installing the new boot (many find this tricky, so here are the 'secrets':
Method #1: Push the rubber back on itself & push up onto the cable with the large end upwards (pushed back on itself). You will then be pulling the large end downward, so the small end stays upwards.
Video: https://www.youtube.com/watch?v=_LQ27c7rX80&feature=youtu.be
Method #2: Install a piece of shrink tubing; lubricate it with one drop of dish detergent. Push the boot up. You can do this without the tubing too.
Method #3: It is possible to use a tapered device such as the tip from caulking tubes, & with removal of the end parts, use the taper tool, with perhaps a bit of grease, to slide the boot up, etc.
It is critical that the rubber boot does not allow water to get into the transmission. That has been the cause for many $$$ transmission repairs.
The typical indication of water in the transmission is transmission oil that looks like creamed coffee. My suggestion is that you seal the new boot. Some add a lot of grease inside the boot. I do not like that idea, as it can defeat the breather design. If you look at the outside of the cable drive part that is located inside the cable-fitting-hole-area, you will see that it is grooved for a reason, vapors must be allowed to escape, plus the oil must be free to return & stay in the transmission. Some folks use a zip tie over the top small end of the boot. That is also a poor idea, in my opinion. That is especially so if the zip tie is a larger one or is just a bit too tight. The tightening of the zip tie makes the top of the boot squeeze out-of-round, & can actually make things worse for water getting inside. Sealing the boot properly is simple. After you install the new boot (ncluding pushing it completely over the flange of the adapter in the transmission hole), then push the top of the boot (the top is the small upwards end of the boot) downwards some, so as to expose more of the cable sheath that was inside the top of the boot. Clean that exposed sheath area with acetone or other fast drying solvent that leaves no residue, using a clean rag. Be sure it is well-cleaned. Put a small amount of black RTV sealant or your sealant of choice at the top. Smooth it nicely with your finger; then slide the top back up to normal position, then add a bit more sealant. Smooth the sealant junction with your finger-tip so it looks nice, & let dry overnight. After the sealant cures overnight use something like Armor-all or 303, etc., on the entire boot. That greatly prolongs boot life, as the rubber compound BMW uses is adversely affected by smog & sunlight. Coat it again now and then. DO remember to inspect that boot now and then. PUT THE INSPECTION ON YOUR SCHEDULED MAINTENANCE LIST/CHART!! Accordion boot at driveshaft, breather ....& boot swelling: The hollow bolt is the only breather for the transmission on most models, and the driveshaft. A clogged bolt is often only noticed in very hot weather, when the large accordion boot may swell up. The pressure can force oil out of the boot. The earliest 4 speed transmissions did not have a vent hole at the rear of transmission, located above the output seal, forward of the U-joint flange area. Thus the accordion boot tended to swell-up, as the driveshaft area heated up. Leave it alone, unless you love playing with things like removing the transmission, removing the flange (special tool and big forces required), and drilling or otherwise machining a tiny hole in the transmission output flange area (at 12:00). Control cables, additional notes: Some of this article's below sizing information may seem to conflict with Anton Largiader's page. We made the measurements somewhat differently (and there could always be errors). Unfortunately, some of my information was lost, when/if I find it, I will add it to this chart,
below. There is additional information here: http://www.siebenrock.com/en/. It is easy to find a part number for any particular bike model & year, on any on-line fiche. What is NOT easy is to find out, at least not always, if yours are high, medium, or low bars; but, especially, if you are making changes, not just in the bars, you cannot search for cables by length. In my article you are reading, in the chart below & in Anton's article, you can see the lengths! Note that some cables come with the rubber boots at the end(s). R65LS low bars are a black version of the R90S/R100S bars. R65LS high bars are similar to /6 and /7 US shipped Hi bars models, but are black. Fuel cables, or throttle cables, may be listed as Accelerator Bowden Cables. Control cables are often listed as a Bowden...which is not a brand name but is a descriptive name. Refer to http://largiader.com/articles/cables/ for further information on cable lengths and what is meant by "length" and "free length". My information is primarily for bikes shipped to the USA. In some instances the Euro bikes, or Canadian bikes, etc., have 40 mm carburetors instead of USA bikes having 32 mm carburetors, and this may require different throttle cables. In my chart below I may have the part numbers and length for some of those, and if so, they are identified for you. If replacing cables due to wear, there is usually a BMW part number printed on them! Model of BMW, if known Where used Length, sheath & over-all. BMW part number Notes /6/7...to 1984 or 1985 Clutch 1386, sheath 1155, overall 1410 32732324958 32732324959 /5 standard Clutch 1320, sheath 1085, overall 1345 32731230041 /5 Hi bars 1460, sheath 1225, overall 1485 32731230042 /7 on, RT, GS, G/S 1495, sheath 1285, overall 1520 32731235956 K75S Clutch 1510 32732324955 R45 and R65 Clutch 1361, sheath 1130, overall 1386 32732324959 K100, K75, K1100 Clutch 1625 32732324960 R45 and R65 Clutch 1469, 1242, overall 1495 32731237694 R80/100 Mystic, R100R Clutch 1410, 1180, overall 1436 32732324957 Many Classic K models Clutch 1510 overall 32732324955 Throttle 528 mm, some literature says 517 mm 32731242135 Throttle 1158 mm 32731454584 Throttle 1118 mm 32731454585 R100GS Throttle 1130 32731454090 91-95 R100PD Throttles 1143 1178 32732311827 32732311828 Throttle 675 32731242128 Throttle
765
32731242127
Clutch lever at bars 32721230871 Perches (those easy to lose wedges at the controls): These tiny triangular-shaped metal wedges keep the controls from slipping, and also keep you from damaging the controls when you tighten them at the handlebars. Here is a sketch-drawing, in case you want the dimensions; perhaps you will be making some, or just want to know:
They are shown on BMW fiche on the sketches of the handlebar controls. These came in different finishes, depending on year, etc. Perches were used on R26, R27, R50, R60, and R69 models (up to 1969). Perches were also used on the Airheads (all models up to 1985 only..?). NOTE: BMW handlebars are 22mm. BEWARE! Some folks have installed 7/8" handlebars....this can lead to broken controls, ETC. The part numbers for these wedges are: 32-72-2-072-233; 32-72-1-232-929; and 32-72-1-242-626, etc. Various names have been used for them, including perch (some use that word for handlebar risers, however) and commonly wedge. The German word is Keil. BMW modified the top cover and gasket of the on-bars rectangular brake master cylinder, mostly due to problems of warpage and leaks. See:
https://bmwmotorcycletech.info/brakes.htm.
Failure to understand what changed, etc., can cause you to use the wrong cables, or, the existing cables may not fit. Revisions: © Copyright 2020 , R. Fleischer
That is their English start page, but navigation keeps changing, so you will have to navigate the website to find the cables, & you might have to do a site search, & then translate to English, perhaps wholesale translation, via Google (Google browser users can turn on automatic translation service; or, use their translation page).
FL = free length.
overall 1386
Low bars for both of these.
Low bars, standard
Hi bars
Hi bars
Lo bars
Hi bars
High RT & similar high bars
and many early Airheads with high bars
Lo-medium bars
40 mm carbs
32 mm carbs
32 mm carbs
32 mm
1165
When a GS is upgraded to 40 mm carbs, probably will use above two cables.
32731454091Left cable
Right cable
R100R; R80R R100GS, PD
84 FL
40 mm carbs, Left cable.
40 mm carbs, Right cable.
High bars, upper cable
All, since ~1976
32721232662waverly washer
Nylon-like bushing
https://bmwmotorcycletech.info/Airhead-Controls-Wedge-Perch.pdf
For photos of them in use: http://w6rec.com/duane/bmw/perch/index.htm.
04/26/2007: Add information on throttle gears and cams.
01/14/2010: Remove clutch cable from title, minor changes in article to clear up grammar & ensure clarity.
06/16/2011: Clean up some, clarify a few details.
09/24/2012: Minor editing; add QR code; add language button; change Google code.
11/13/2012: Add more to cables sections, show article in two places, 7B and previously unused 64.
01/06/2013: Add Perches section.
04/06/2013: Remove as duplicate article 64.
05/09/2013: Incorporate speedo rubber boot information, prev. in miscl.htm. Add another link to another of Anton's articles.
05/24/2013: Add introduction.
05/15/2014: Recheck article, very minor changes, mostly for clarity; add hint on assembly of throttle and cam.
08/03/2014: Somehow my own cable chart listings disappeared during the 7B and 64 interchange. Added a blank table, and will attempt to re-constitute what I can find in my existing notebooks.
08/05/2014: Started filling in that table. Next to do: SNABB and Fiche work to be sure table information is correct, and expand usage, and clarify partial part numbers.
08/08/2014: Finished for now. Cleaned up and uploaded 10/04/2014.
07/22/2015: Add more to section about clutch cables (regarding the transmission located lever).
02/05/2016: Increase font size. Narrow the article. Metacodes updating, ETC.
05/25/2016: Revise article, eliminate redundancies. Add part numbers for waverly washer and lever bushing. Minor clarifications.
12/06/2016: Expand information on perches/wedges, for clarification.
12/07/2016: Add video on how to install boot.
08/23/2017: Rework entire article for fewer font changes, fewer colors, improved layout, etc.
12/16/2017: Minor cleanup.
07/26/2018: Minor clarifications.
04/08/2020: Correct grammar. Clearer explanations.
Last check/edit: Monday, December 07, 2020