OK, here's a weird one!

Riding along today, knock it up in to 4th, looked down and the gear indicator said 5, OK thinks I, drops it down one and it goes to 3! After a bit of flicking up and down I realise that the bike is going through the gears fine, 3rd to 4th to 5th and back down, however the gear indicator is not playing, when in 4th it still says 5 when I knock it up to 5th it still says 5 and then back down to 4th and it still says 5, down to 3rd and it says 3! 

I know that sounds more confusing than it needs to be and in the grand scheme of things doesn't make much difference as I ride in the gear the bike needs but it's just bothering me now. Everything else works fine, the ride is smooth and the gear selection is easy. I'm not a lover of electrics in any shape or form but I absolutely hate motorbike electrics, they just confuse the hell out of me!

So, if anyone out there has ever come across this before I would love to know the how's and why's and if it's an (easy) fix.

Cheers all

Dave

Davep 

The chances are is the indicator switch that is playing up, mine wasn't working in some of the gears, so replaced the indicator switch that is at the back of the gearbox, bit awkward to get to.

If I remember rightly you may have to remove the rear swing arm. 


Hope this helps.

https://bimmercat.com/bmw/EN/search/selectCar/89V1/ohne/BMW+K+100+RS+%280523%2C0533%29/ECE/23_1154

The switch is subjected to water and road crap. Sometimes they will resurrect themselves when they dry out. You can remove them and disassemble and clean. It is worthwhile waterproofing them when refitting with silicone or in my case Plasti Dip.
Regards Martin.

And sometimes that will crumble to pieces when you attempt to remove them.

duck wrote:And sometimes that will crumble to pieces when you attempt to remove them.

Yup, lost one and successfully rebuilt a second one with silicone

The switch is fairly easy to service...once you have it off the bike.  You need to remove the swing arm and the battery mount to get it off the bike.  That can take a couple hours depending on how experienced you are.

The insides are full of tiny springs and bits you need to be careful not to lose.  As long as you are careful and take your time you won't have a problem.  I work on my switches in a shallow plastic food storage container about 10"x10".  A very fine point tweezers from a hobby shop makes handling the springs and contact pins easier.  Deoxit and an old toothbrush work well to clean the parts.

The main problem I have seen with the two switches I've had to service is the potting compound used to seal off the wires on top of the switch.  I looks like it was some kind of wax that over the years has hardened and cracked, allowing water to work it's way into the working bits and screw up the operation. 

I carefully remove every bit of that stuff and clean the part really well with lots of 91% rubbing alcohol applied with small brushes and Q-tips.  After it dries overnight I mix up some slow setting epoxy and cover all the wires and connections on the top with it.  I let the epoxy cure overnight before reassembling the switch.  The joint where the switch splits is sealed with a couple wraps of self-amalgamating tape.

Reinstall the switch with Allen head screws.  They are much easier to remove and reinstall when the body of the switch is wrapped with a bit of tape.

As pointed out, your gear switch is acting up. Based on your symptoms, the Yellow/Blue wire on the switch is permanently open circuit. That could be the switch itself but more probably it is the connector contacts that are corroded or weak, not making contact. Try reseating the TGPI connector on the right side of the bike frame. Also give it a cleaning and check that the metal connectors are in good shape.

I bet if you cycle through the gears, you'll see the following on the gear display: first=1, neutral=1, second=3, third=3, fourth=5, fifth=5

Dave, before taking out your swing arm to get at the switch, try this idea that I've been using for the last 25 years or soon both of my K's.

https://www.k100-forum.com/t6936-gear-position-switch?highlight=gear+position+switch

For the few pence that resistors cost it's worth trying.

Paul.