R26 speedometer woes

Begonnen von BSA Bob, 03 Mai 2024, 13:16:11

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BSA Bob

The needle on my speedometer constantly waves wildly around the dial, sometimes worse than others. It's been looked at twice by a gauge repairer with a good reputation, & I've tried 3 cables. Today I had to disconnect the cable at the gearbox drive, & even with no drive the bloody needle still jumped wildly a couple of times before I got home.
Can people give their opinions on what could be  wrong?

BSA Bob



strichzwojan

Hi Bob, die VDO-Tachos sind leider die unzuverlässigsten Bauteile an einer BMW...
Sie sehen nett aus, gehen aber leider immer wieder kaputt. Das Pendeln kennt wohl jeder. Manche geben der Tachowelle die Schuld (hast du ja dreimal gewechselt), einer schlechten Schmierung derselben, einem zu weit überstehenden Vierkant an der Seite, wo die Welle in den Tacho gesteckt wird. Im Inneren des Tachos spielt wohl ein dämpfendes Silikonfett eine gewisse Rolle, was seinen Platz verlässt, wenn man den Tacho falsch - also auf der Tachoblattseite stehend - lagert.
Originale alte VDOs haben oftmals "Zinkpest", ein Korrosionsproblem, was auf Verunreinigungen im Nachkriegsmetall begründet ist.

Mein Tacho benimmt sich bis 60 km/h vorbildlich, aber ab etwa 80 fängt er an weit auszuschlagen. Wenn ich von der Autobahn herunterfahre, dann braucht er eine gewisse Zeit, wieder normale Werte anzuzeigen. Außerdem zeigt er zuviel an, wenn es steil bergauf oder auch bergab geht.
Ich habe mich daran gewöhnt, die Geschwindigkeit zu schätzen, was vermutlich sowieso genauer ist.

rolf.soler

Does it work when you turn the cable with a accu electric drill (counterclockwise !. Just put the square gearbox end in the drill jaws, start turning slowly and increase speed.
Probably won't. I suspect the speedo is bad...have it repaired again or buy a new one from BMW mobile tradition...if available. I bought several new ones over the last 15 years, they are all fine.
I hat needle waving too at times, but it was always the cable...most often it was not properly seated in the gearbox, or the speedo

cwf

Hello Bob,

Is the speedo a magnet revolving in a cage, ie the magnet is attached to the speedo cable, the faster it turns, the further round it drags the cage, which has the needle attached?

That was the /6 and /7 type and I worked on them many times. If it is, and the speedo cable is not the cause, I felt the problem was lack of lubrication somewhere, so there was 'snatching', ie slight slowing down then speeding up.

If you pull the needle off its spindle, and you'll have to be careful without a proper puller, note that the needle is 'preloaded' against the stop.

Charlie.

4Taktix

Hi Bob,
if your needle waves without connected cable and there ist obviously no visible damage for a gauge repairer,
it is highly likely a weakened spring. May look proper, but doesn't have enough tension to push the needle
against the stop.
Or else it might be, that somebody in the past already pulled the needle off, but didn't mark the 'tensionless'
position before and pressed it on in a slightly twisted orientation, thus the lack of tension against the stop.
Do you want to open the speedo yourselves ?
Did it read approx plausible speeds - average during waving ?
Does the needle also wave, when the bike is in neutral and engine running/reving ?

Cheers,
Sascha

Think outside the box !

BSA Bob

Thanks for all these replies.
cwf, I'm pretty sure my speedo is of the type you describe, others would know better.
I've since tried the speedo with the cable powered by a drill. It ran OK up to about 60km & then made a loud grinding, rattling sound with the needle going everywhere. With everything stopped the needle's now stuck on about 40kph.
I've put a speedo from a twin in as a place filler, it runs smoothly but of course gives the wrong readings.
I'm now considering my options, I fear the original is badly damaged again.
I notice there's a similar speedometer issue on the main mechanical thread here, & I'm following that.

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