Erratic Speedo

[BooG]

This prob has been around for a while. Get to about 80mph, and the needle on the speedo goes AWOL: flying around the gauge and then settling on a ridiculously high reading. I have opened up the speedo to investigate. I am unfamiliar with its workings, especially the "clutch" type discs and the thin needle which joins them. Anyone know how they work and what to look for? Heres a photo.

[mikethebike]

Not sure if this is same one but may be worth a read for info:-
http://www.airheads.org/content/view/160/98/
or this one:-
http://home.jtan.com/~joe/speedo.htm
Mike

[BooG]

Cheers Mike! Exactly what I needed. Let the surgery begin!

[mikethebike]

You're welcome.  Keep us informed. I've never tackled one myself but they look very fiddly!  :-/

[BooG]

Had a go and a test run, but showing up about 10mph slower than should be. Another go.......

[not-so-fast-ed]

Let us know how you managed to get it working.  Many of us are in the same boat and would like to get the odometer/speedometer working and more accurate.
Thanks,  Ed

[J_Hirst]

Anyone ever opened up their speedo?  can't figure out how to get the ring off of the front.

The ABC link shows them opening up the intrument cluster off of a R100, which is completely different.

While Blue is in pieces, I'd like to address the speedo problem.

[k_enn]

Interesting thread.  But it does not seem to help with my problem.  The erratic nature of my speedometer is not that it just stops, or runs low, but that it also runs way high at times.  The issue is more one of inconsistency than straight out inaccuracy.  For example, yesterday when I was riding I noticed that it was at zero.  I tapped the speedometer lightly to get the needle off of zero.  Well, it went off of zero, and kept climbing.  It was reading 80 when I was doing about 50.  I stopped for a traffic light, and it quickly dropped down to about 25, but took another three or four seconds to drop down to zero after I was at a dead stop.  When I resumed riding from the traffic light, it was again reading way high.  It was like that all the way on the ride home.  About a half hour after I got home, I took the bike out again and the speedometer was operating back in the range of "normal."  

Any ideas?  It doesn't sound like a slipping gear would account for an excessivley high reading.  I would like to avoid replacing the speedometer, since it is relatively new (replaced a couple of years ago, and has only around 5,000 miles on it).

k_enn

[Justin B.]

Jonathan, you have to "uncrimp" the black ring around the perimeter.  I have done a couple but have never had good luck "re-crimping" the ring and always wound up JB-Welding it back on...

k_enn, it sounds almost like something is rubbinbg or hanging up and catching.  I have dealt with jumpy needles before but nothing as bizarre as you are describing.  The drive gear bushings on one went bad that caused it to intermittently go from reading correctly to the needle bouncing all over the place but it never stuck like you are describing.

[Darwin_R65]

the clutch mechanism you describe is actually a magnetic drag cup.

the magnetic disc spins and the faster it goes the more it drags the needle against the hair spring.
the jewel is the seat on which the needle sits. (the cup has the needle poking from it.)

the surface between the needle and jewel are meant to be be very low friction. If you have any contaminant, or wear they will tend to grab and drive the needle higher than it should. NEVER oil or grease this.

I am currently looking at my speedo as well. Speedo is OK, Odometer is dodgy.

Here in Australia I've been quoted A$600 for another speedo. I think a repair will cost between $150 and $250. That's a guess, the last speedo i had repaired was a Smiths from a Hillman Gazelle by the same company I'm about to use, with more wrong than my BMW has.

At the time I decided a repair was the same cost as a speeding fine, so I didn't hesitate in sending it off for repair.

I pulled mine apart last night and discovered I need parts replaced. So the DIY repair is out of the question for me.

John

[Darwin_R65]

And yes uncrimping the face plate is a bit of a skill.
I use a small flat blade screwdriver and slowly move around uncrimping slightly. (no need to fully uncrimp the edge all at once)
you need patience or else you end up with an edge that looks like someones butchered it open
Then it also takes a delicate hand to tap the edge back over when replacing it.

try not to get finger prints on the face after you remove the glass, as the oil from fingers will show up very well.
I undo the two screws and then actually gently pry the whole face up to remove the needle with it.
when replacing the face, do up the two screws and then another frustrating task is replacing the needle in the correct location, or else your speedo will read high or low.
you need to place the needle on so that it is just clearing the needle stop by a hairs width. If there's too big a gap, it will read that much too high. If it is pressing against the stop, your speedo will read low, depending on how much it is pressing against it.

John

[MrRiden]

I've had mine apart at least three times for various malfunctions. First was erratic reading and I discovered that what Darwin_R65 posted was the fix. The second was for the odometer. Due to the speedo being a big rain cup the shaft that the odo digits ride on had rusted, I fixed this with a length of brass rod / wire sourced from a hardware store. The third was the needle falling off. I reset it with a bit of retard against the stop pin fastened with a drop of red loctite. It now reads somewhat less optimistic. As for the bezel, there is no elegant way to un-crimp it. A careful hand and a thin blade seems the way to go. Likewise re-crimping takes a careful hand for less than perfect result. I have in mind a circular jig with the profile of the crimped edge routed into a split circle of hardwood. this could be slowly compressed and repositioned during compression to produce a good result. I just need to find a friend who has woodworking skills / tools and a source for new bezels.
rich

[k_enn]

Thanks, Darwin.  The speedometer was back to normal today, but if it acts up like that again I try what you mentioned.

k_enn

[drewboid]

Eratic speedometer readings can also be caused by a cable about to fail. Mine was being eratic one day and suddenly went all the way around the dial several times. Wrecked the hair spring inside.

[BigJohn]

Another source of speedo problems is the angle drive assembly at the back.  Make sure the bevel gears have some white lube on them.  Mine didn't and the needle was all over the place but became steady as a rock after lubrication.  These can be greased without removing the bezel! It's worth a try before opening the speedo.