‘87 K100RT with Speedometer & Odometer Issues

[RK Ryder]

My ‘87 K’s speedometer and odometer are not working; the tach and clock are fine. The speed sensor wire from the rear wheel is fine; been tested. The problem seems to be the wire which joins the rear wheel sensor wire. These wires connect near the bike’s computer, under the seat and close to the tank on the bike’s left side.

 

The wire that I am certain is the problem is part of the bike’s wiring harness. My assumption is there is a break in the wire which needs to be cut and have a new piece spliced in place.

 

The non-dealer BMW mechanic who has yet to check the wiring thinks that replacing the speedo unit that he has will be the solution. However his unit reads about 37;000 whereas mine is 284,000. I prefer to keep my original unit.

 

My question is for those with more skill and knowledge than me.

 

What is possible solution is more likely correct; a replacement speedo or checking the wiring for a fix?

 

Your input is very much appreciated as he is going to be looking at my K in a few days time.

 

Paul

[dirtrider]

On 8/31/2024 at 3:31 PM, RK Ryder said:

My ‘87 K’s speedometer and odometer are not working; the tach and clock are fine. The speed sensor wire from the rear wheel is fine; been tested. The problem seems to be the wire which joins the rear wheel sensor wire. These wires connect near the bike’s computer, under the seat and close to the tank on the bike’s left side.

 

The wire that I am certain is the problem is part of the bike’s wiring harness. My assumption is there is a break in the wire which needs to be cut and have a new piece spliced in place.

 

The non-dealer BMW mechanic who has yet to check the wiring thinks that replacing the speedo unit that he has will be the solution. However his unit reads about 37;000 whereas mine is 284,000. I prefer to keep my original unit.

 

My question is for those with more skill and knowledge than me.

 

What is possible solution is more likely correct; a replacement speedo or checking the wiring for a fix?

 

Your input is very much appreciated as he is going to be looking at my K in a few days time.

 

Paul

Afternoon Paul

 

If you have an AC electric soldering gun or better yet an old style soldering iron then plug that in & try moving it around near the pickup end of your rear speed sensor. Not all but some soldering guns or irons put out a 60 Hz signal. With key-on that should indicate something over 60 mph. If it doesn't work then you still won't know if it is just your soldering iron or if your speedometer system has other issues.

 

Otherwise, if you have a small digital volt meter with a low

A/C voltage setting then put it on the lowest  A/C voltage setting that it has then hook it to your rear sensor then spin the rear wheel (you should see a low voltage output (how much I don't know). If your K bike has a front wheel speed sensor you can use it's output as a comparison. 

 

Those old K bikes are difficult enough to diagnose with the bike in hand & way more difficult over the internet.

 

 

[RK Ryder]

Thank you for your reply Dirtrider.

 

Paul

[Lowndes]

You might try a temporary test wire from the sensor to the speedo. EZPZ.