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5 speed transmission,
neutral switch testing and replacement.
Copyright 2023, R. Fleischer

4 speed transmissions have an internal neutral position contact, and a single wire fastens to it on the rear of the transmission.  This article is not applicable to the Airhead's 4 speed transmission, which does NOT have the various complications of the 5 speed neutral switch circuitry.  The 4 speed transmission neutral switch is used ONLY to indicate neutral by illuminating the neutral lamp.  Leaks at the 4 speed transmission neutral switch are rare, and easy to seal.  The rest of this article deals with the neutral switch mounted on the bottom of the 5 speed Airhead transmission.

The switch located at the clutch lever on the left handlebar on 5 speed transmission models is not the true neutral switch to illuminate the neutral lamp, although it functions with the real one, but not in the same way.  The switch under discussion in this article is the switch located on the bottom of the 5 speed transmissions.

Don't do a neutral switch replacement unless you are sure the problem is transmission oil that is leaking from the area, or you are sure that switch has electrically failed, or, you are changing the internal cam assembly to the later type (AKA 'shift kit' model).  You may be able to repair a mild weeping or small leak from the switch itself, using the procedure shown later in this article, although the switch should be removed for ease in doing the fix.

There are two versions of these switches, so be sure you get the right one for your bike.  The switch function was reversed in the 1976 model year (beginning September 1975), and they look sort-of similar.

The stock 1974-1975 year models 5 speed transmissions used a neutral switch with a somewhat shorter stem than the 1976 and later, the older switch was 61-31-1-352-153; which became 23-14-1-352-153.  Along the way was 61-31-1-358-142; all were OK numbers.  A thin washer is used on the early switch.   Various literature will show that washer as size 12 x 15.5, and the number as 07-11-9-963-130.  That washer was used at two other places on Airheads:  (1) 4 were used, two on each side of each of the banjo bolts for the oil cooler; (2) the same -130 washer was used on some fork lowers, the center bolts at the bottom.

The 1976 model year and later transmissions use switch 61-31-1-243-097 (see 61-31-1-355-262).   Some 1976 transmissions were earlier 1975 models but may have the earlier "1974-5" switch.   The change from one switch to the other did not occur exactly with the change of model year, so be careful.  The later transmission located internal cam plate uses the later switch.

For the 61-31-1-243-097 (see 61-31-1-355-262) switch you must use one special "2 mm" thick washer (do not use a common drain plug gasket washer!).   Reports of BMW having shipped the wrong part have been seen.   Tom Cutter measured a new one and it was 19.8 mm x 12.35 mm x 1.89 mm.    Original new ones, which might fit better (?) are probably 2.0 mm thick, but this is not important.  If you forget to install this ~2mm washer the neutral lamp will NOT work correctly, no matter which switch you have installed ...and you may have shifting problems.  The reason the switch was changed is that the updated transmission shifting cam uses valleys to positively locate the switch plunger; while in the prior version the switch plunger rested on the 'mountain-tops' on the shifter cam.

If you have pulled the transmission rearwards to, perhaps, grease the input splines, it is then easier to remove and replace the neutral switch.  If the swing arm is pulled to the rear somewhat, you have more room.  The effort varies with the models over the years.  If the transmission is out and on the workbench, the switch fix or change job is very easy. do NOT have to pull the transmission backwards nor do you have to remove it, to replace the switch.  It really is far better to remove the switch if trying to seal a leak from an existing switch.   With the transmission in place on the engine, you must remove the long aluminum spacer in order to get to the switch.

Most folks with an electrically bad, or oil-leaking neutral switch, should do as follows:

FIRST, determine that the switch really is leaking oil; or, that the switch is actually bad.  Testing is relatively easy using methods such as cleaning with a solvent and then taking a ride and blowing talcum powder at the area, etc.   The rest of this section assumes the switch is going to be removed and repaired for leaking ...or possibly replaced due to switch failure.

Place a support under the engine oil pan, perhaps sturdy large blocks of wood. Be sure to support the oil pan on something like wood blocks.  Loosen the front engine mounting stud don't have to loosen it much more than a full turn.  These pre-steps will usually make the follow items easier to do.

The long round aluminum spacer underneath, that the rear motor mount stud goes through, is in the your way for access to the neutral switch. The rear long steel engine mount stud passes through the frame, the spacer, and the frame again. There is a washer and nut at both ends of this long threaded stud.  You need to remove that stud and then remove the long aluminum spacer.  Replacing the switch is then relatively easy.   The question usually is how to remove that long stud, sometimes it is quite tight.  I sometimes just use a soft brass or aluminum rod I have, with a dead-blow hammer.  You probably don't have such rods, so, here is a nice method, one that you may want to put into your personal memory bank:

The following is called the "draw-bar method".  This method is sometime used to draw out piston pins, etc.

Drawbar method:

1. Remove the nut & washer from one end of the rear engine stud ....let us say the right side.  Which side is unimportant, pick the one you like. You can use oil if you wish on the stud you removed the nut and washer from, in this example, I selected the right side.   Sometimes oiling the exposed outside threads helps when pulling/drawing out the stud.   Use additional oil, if needed, as you proceed.

2. Tighten up the remaining nut this case the left side nut ...until you just about, but have not, reached the end of the threads.  Almost always the stud will not rotate as you tighten towards, but not to, the ends of the threads, after all, the stud usually has a lot of friction, which is why you are using this method.  If the stud rotates easily before the nut reaches the ends of the threads, it likely will come out easy, or at least in part easily use of a rod and dead-blow hammer on the right side.

3. Remove the left side nut & put any convenient metal spacer you have lying around over the stud, leaving enough room to enable 3 or 4 threads, which is a safe minimum number of threads to be engaged by the nut. You can start with some large washers, then graduate to any old socket that fits, with a washer if needed; or ...pieces of pipe ...whatever.

4. Again tighten the nut to near the end of the threads. Repeat by adding spacers, washers, sockets, whatever. Oil the right side if you want to try that to enable the stud removal.  I use a spray can of light oil. Notice that each time you do this 'drawing-out', the stud will be drawn out more to the left.  Continue to 'draw out' that stud by the process described until you can pull it out by fingers or a tool gripping the nut.  Clean the stud carefully want it SMOOTH when you reinstall it later on. I usually do a coarse polish job on the stud with a motor-powered rotary wire brush.  If you have not loosened the front stud a bit, and blocked up the pan, this drawing-out can be more difficult.

5. The next thing is to remove the long aluminum spacer. It is almost always wedged in tight.  It needs to be reasonably tight when replaced.   You will have to do some prying, so be careful, do NOT bang or pry on anything you shouldn't!  Usually one simply pries a TINY bit at one end, then the same at the other end, back and forth, working the spacer out slowly.  I like to leave no marks, and certainly not break or crack anything, especially the transmission fins/etc!  I may use a small piece of wood, or whatever is handy, to avoid pressing on the wrong areas.   A proper shaped pry bar will also work nicely, consider padding it or using a piece of wood, etc.  Don't injure fins, etc.

During this process of removal of the long spacer, do not push the spacer forward ...the whole idea is to remove it towards the rear for removal.

Sometimes just loosening the front motor mount will enable the spacer to loosen up some!!....due to various side forces including the springyness of the frame, and fitment of the studs, already did that, and supported the pan,  ...YES?   Note:  I made a tool to push the two frame members apart (by a few thousandths only), since I did this job rather often; and with the rear motor mount loosened, and front slightly loosened, it worked pretty good.  Some have tried loosening the swing arm, with little help.

6.  You need to drain the transmission oil!  If the oil has 8K on it or more, don't save it, plan on installing fresh 80W90 GL5 oil.

7.  With the spacer removed you now have access to remove & install the new & PROPER part number switch, suitably sealed first, as I recommended.

Switch leaks & preparation (new or used switch) for installation:

The switches were made with electrical spades pointing sideways (later types), and also made with them pointing downwards (early types).  With the downwards type, it is easy to use a deep socket or wrench.   With the sideways type, you will have to use an open-end wrench unless you have made a special socket tool.   Do not bend nor pressure the spades!  Do not warp the body! Switch bodies are much LESS likely to be warped by using a socket or box type wrench, so DO use a socket or box wrench.

Even brand-new switches (from BMW, and other sources!) can leak right after installation or after awhile. There is something wrong with the construction. BMW has been informed.  So far, no BMW fix.  The type of leak usually seen is a very slow weeping at the junction of the insulation and the metal body ...or ...leaking from the spades where they go into the body.   I have heard from several sources that Motobins sells copper (brass?) bodied types that do not seem to leak.   However, a noted Airhead Guru, Tom Cutter, reported on 05/04/2015, on the Airlist, that he bought twelve of part 76700A.  Seven were dimensioned incorrectly so that they did not switch reliably. Two leaked immediately on installation. The last time he ordered, they filled the order with OEM switches.  Tom reported on 07/01/2015, that he had purchased SIX from Siebenrock; and of that SIX, 2 did not work, 2 had threads too long, and 1 leaked.

I have had reports of good results with this gold colored switch from
61 31 1 243 097    This is for the later switch (after 09/1975).

The earlier switch from them is 23 14 1 352 153.

I recommend that EVERY switch, NEW OR USED, have the following done to it before installation or re-installation:

I will no longer install any 5 speed transmission neutral switch, new or used, from any source, without doing the following; and, remember, do not over-tighten, do not warp the body, and do not bend the male spades.

Using a quite sharp dental tool or other sharp small thin 'tool', get right into and scratch quite a fair amount at the junction of the metal body and plastic/bakelite insulation. If you want to seal the spades, do the scratching around them too.  You want a clean but lightly rough surface before applying sealant. Use a tiny piece of fine sandpaper, and rough-up the metal and the bakelite insulation, of that junction of the metal body (and spades, if so doing) to the hard plastic insulation section.  The idea is to sand the junctions areas for maybe 1/8" width minimum, right into the junction ...and then clean that area with a strong evaporating solvent.  Non-oily acetone is what I use, non-oily means not using your wife's fingernail polish remover. You can use MEK, etc.  Then apply a fine to moderate wet line, all-around, it need not be all that wide, of a thin viscosity 'wicking' Loctite.   I like to have the switch warm when I do the application of the Loctite.    Do this with the switch standing with the terminals upwards, threaded end downwards.  Make a little wood stand or use a little vice on the hex (do NOT tighten much).   Let sit, a full day, preferably in your warm houseThen clean the junction with a thin rag goodly wet with acetone or MEK, etc.

I then apply epoxy to the junction (yes, I use a double sealing method!), completely around, covering the junction. You do not need large amounts.   Either 5 minute or 24 hour epoxy, but I prefer the slower-curing epoxy.   Let it cure one full day, even if the 5 minute type.  Then install the switch ...being careful to install the proper washer, and tighten with the proper tool and do not over-tighten.  If you over-tighten, you can distort the bond and it may leak. The tool you select may depend on the particular switch and terminals orientation, as noted earlier. and what tools you have. Be sure the switch works properly before installing. You may want to further test the switch: 
If the transmission is out of the motorcycle, test with a continuity tester or ohmmeter, as transmission is shifted. If the transmission is in the motorcycle, rotate the rear wheel to help shifting, use neutral then gears, back and forth, to test the switch.

8.  Clean the spacer bore with a brush, or, whatever method you wish ....and then do similar cleaning of the frame areas the stud fits through.  I typically use old gun brushes, sometimes thin strips of old sheeting, dipped in solvent, etc.

9.  Install the switch into the transmission. Don't forget to install the proper washer,  using the special washer with the later style switch.

Do not over-tighten the neutral switch!   Be careful not to distort the switch body nor the spade connectors.  With switches that have prongs downwards, that is easy, use a proper depth of socket.  Do not overtorque!

***If the switch is OK, but just weeping or leaking a bit, you can likely fix the leak, using the procedure I outlined above.

10.  After you replace the switch/washer, and before you install the aluminum spacer, do not forget to install the wires!  If they do not fit moderately tightly onto the switch male spades, squeeze, slightly, the females.   It is a VERY good idea to test the switch electrically as previously noted; to be sure the switch is working.  Once connected, the neutral lamp should be lighted ONLY in neutral.  If you have the lamp on in all 5 gear positions likely installed the wrong switch.  The proper washer is needed too.  Check to be sure you did not pinch wires.   Both styles of neutral switch close their circuit to turn the light on.  The difference has to do with the cam changes.   That is, whether or not the switch plunger sits on a hill, or a valley of the cam, in neutral.  Thus, the physical direction for switch operation is reversed between the two styles of switches has its plunger OUT for turning the switch ON, the other has the plunger inwards to turn the switch ON.

The two push-on wires to the switch can be interchanged at the switch; either can fit to either terminal.

Some switches seem poorly made internally, and do not work properly ...yes, brand-new ones.   I always test switches before and after installing them. I always seal the switches.

RE-installing the long aluminum spacer:
Read this through ahead of time, and then you will be ready when the time comes.   I have already had, much earlier, my small floor jack under the oil pan ...lightly pressured, and position-biased towards the rear of the oil pan, because the rear stud was going to be removed early-on, and, with the front stud slightly loosened, you don't want the motor falling any.  In replacing the aluminum spacer, you may find you need to slightly adjust the jack if needed, mind the fins of course, etc.  I originally used a piece of wood on the jack to protect the pan fins.  The jack can be used to line up the rear frame and the spacer you will reinstall, etc.

1.  Clean the long aluminum spacer if not done already, inside and outside. I've already mentioned this. I sometimes use a gun cleaning kit and bore patch with solvent.  Good use for Hoppe's!   Put a slight smooth radius (16th or 32nd.) on the sharp ends edges.  This does not mean a 1/4" radius! What you want to do is smooth the edges at both ends, so it installs easier, yet not much contacting end surface area will be removed from the contacting face.  A piece of sandpaper or a mill file works nicely, or even a drill press with sandpaper or mill file.... if you don't have a lathe.  I have a lathe, and do it with a fine mill file in the lathe, but have done it in drill presses, and in my hand too.  Remember:  NO sharp edges.   When done, and the spacer is still nice and clean, spray the inside of the spacer with any handy thinnish oil.

2.  Freeze the spacer.  The freezing causes it to shrink in length.  In shops, we might quick freeze it to extra cold, with an old carbon dioxide fire extinguisher.  YOU can use your household freezer ....or?.

3.  Check the transmission area, and if any sharp edges, also remove those, carefully. You want that spacer to install fairly easily.

4.  Grease or oil the the stud (I first use a motor driven wire wheel or wire brush on the studs and threads too if cruddy) very lightly over its full length; then install one washer and one nut on one end, such that no threads are exposed outboard of the nut, but as many threads engaged as nut allows. I freeze that stud first before installing; but you probably don't really have-to.

5.  Install the well-frozen aluminum spacer quickly and evenly.   I use thin leather gloves.  Don't tilt the spacer, install it as squarely and quickly as you can,  ...using a plastic mallet or brass hammer, dead blow type hammer, etc. Try to line up the frame and spacer holes as closely as you can, using #1 eyeball.  Use a round tool of some sort (the stud or axle tommy bar?) if you need to, to align the holes of the frame and spacer.  DO NOT injure the transmission case fins.

Install the stud, using a brass or plastic hammer on the end you put the nut (nut flush to stud end).   If you had the internally lubricated aluminum spacer (well-eyeball-centered) still frozen, and the stud greased or oiled, this will go relatively smoothly.  You may have to move the rear of the engine up and down a small amount using a tiny movement on the jack.  Usually I do not have to.

6.  Install the other nut & washer, torque the nuts, keeping the amount of threads proud of the nuts approximately the same on both sides.   The typical torque is to be 55 foot-pounds.

7.  Don't forget to re-torque the front engine stud nuts that you previously loosened!

04-17-2003:  Add .htm title; clarify details.
07-07-2003:  Expand and clarify procedure.
08-24-2004:  Add techindex I.D. number; clarify some details.
02-24-2005:  Clarifications, and again in April 2007
11-20-2010:  Clean up, add part numbers from prior article on same subject, inadvertently left out.
12-05-2011:  Add information on sanding and epoxying even brand new switches.
02/04/2012:  Clarify neutral switches and their washers.
10/11/2012:  Add QR code; add language button; update Google Ad-Sense code.
11/25/2012:  Clean up and revise slightly for clarity, order of events.
04/02/2013:  Minor improvements in clarity; also removed language button sometime in 2013.
05/04/2015:  Add Tom Cutter's remarks about the Motobins switches; and, from Alan, bmw2valve info. 
07/01/2015:  Additional updating for clarity.
03/08/2016:  Update meta-codes, fonts, colors, layout, small changes for clarity.
02/28/2018:  Reduce excessive html, colors, fonts.  Change order of major sections and improve layout.
07/22/2020:  Clean up explanations a bit.  
07/30/2023:  Fix part numbers.

Copyright 2023, R. Fleischer

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Last check/edit: Sunday, July 30, 2023