Bmw K75s speedometer reads 2x speed

[Jbuffalo]

I put this speedometer together from two broken ones.  Everything works except the speedometer and mileage indicator now read about 2 times what they should.    For example 55 miles per hour is now reading  110 mph, travel 30 miles and it reads 60.  Any idea? 

[Inge K.]

Quite logical...if you put two speedometers together, you get the double speed......

 :hehehe Sorry, could not let this one pass, haven't got a clue..




The only thing that I can think of....is that you could try to change the preamplifer PCB, if you got a spare.
It's the narrow PCB that sits in the bottom at the rear side of the speedometer.
Can't say that this would solve the problem, but it's worth a try......

[Chaos]

hmm, I know if you hold a 120VAC soldering iron close to the speedo pickup in the rear end the speedo will read about 45 (?) mph.  Somehow yours is doubling it's sensor rate.  I did find this at http://www.ibmwr.org/ktech.shtml  :


K Bike Speedo Adjustment

By: Brian Curry
November 1996
Rob Lentini and I have been having a discussion on the "adjustability" of K bike speedo's with Rob not being able to find the adjustment potentiometer. I found it and this describes it.

The adjustment pot is on the side away from the stepper coil. It is towards the lights and unless you have separated the speedo from the rest, you will not see it. It is behind the gears that drive the odo, and on the little board that you can see in the unassembled view. This is the board that the 3 pin connector plugs into. This is a high (12V) signal. I think some of it is robbed to drive the electronics for the frequency sensitive circuit that drives the meter that functions as a speedo indicator. Even then it is well buried with the adjustment almost exactly in line with the plastic sheet. This is just like the tach where they obviously don't want you to get your fingers in there.

Now, how to drive it and adjust it. That is for a later time.

But for those who are adventuresome and have time on your hands, you too can adjust your odo.

Brian Curry, Chester Springs, PA, USA

[Inge K.]

The pot.meter is for fine tuning the speedo.........half or double speed is outside its range.

[Jbuffalo]

I just checked to see if I installed  Kph speedometer parts on my "stock" speedometer-no it is a Mph speedometer. Are any of the K bike speedometers different?  This was off 1980 K75.  It reads about 2x not sure.   thanks

[Inge K.]

Have you tried to swap the preamp which I mention in reply #1?

[ReneZ]

There are lots of differences. I just had 3 speedos on the table and they were all different. I bought a bike with a faulty speedo, so thought I would be OK fitting my spare. Indeed, everything worked as expected, but coming home my wife, who drove behind me with the toolbox etc  :yes asked why I was speeding all the time. Rather surprised, as I had been keeping to the speed limits I had a good look at the bikes original speedo and my spare from the UK RT one. The UK RT one has 70 MpH in the 12 Oclock position, but the others both 80 MpH at the top. I thought I was doing 70, but was 80  :eek:. Opening up the original and the donor there are quite a few differences, particularly for the 3-way connector to the speedometer itself and in the way the speedometer amplifier board was fitted.

[bocutter Ed]

I just checked to see if I installed  Kph speedometer parts on my "stock" speedometer-no it is a Mph speedometer. Are any of the K bike speedometers different?  This was off 1980 K75.  It reads about 2x not sure.   thanks

I think the only difference between Kph and Mph is the screen printing on the face plate. I've had both on my bike and have switched speedos between units (my original MotoMeter has oxidization on the wire loom at the input pins).

[Jbuffalo]

No I have not tried any of the ideas yet.  I have to get some time to take the fairing part off and get to the speedometer.