R65 Speedometer question

[R65Biker]

Hi everybody,
When I reach about 70-75 mph, the speed indication jumps to max speed reading. What could be causing this? Cable or speedo itself?
Thanks, Ernst

[montmil]

Have you checked the condition of the speedo's drive cable? Could be dirty, dry or crimped. The speedometer takes its cable drive off the right side of the gearbox. A hollow bolt -which vents the gearbox and should not be clogged- secures it in place. This bolt should never be overly tightened; it strips very easily...$ Snug is good. Also, the rubber boot on the speedo cable, if in poor condition, will allow water to enter the gearbox with unhappy results. Check these items closely.

Got that manual yet?

Monte

[Justin B.]

Could be grunge in the works causing the two magnetically coupled parts to "lock" together...  Usually gets erratic before that point, though...

[tvrla]

It doesn't sound like the cable to me since it should be 'jumpy' before 70mph. But the first thing would be to lube the cable and make sure it has no sharp bends.

If that doesn't do it, then it may be time for an overhaul - clean and lube. When the needle starts bouncing major damage follows.

I fix these things (BMW mechanical gauges) so you can send it to me for repairs. I'm also interested in buying used or junk gauges.

[Semper Gumby]

I don't think the cable is supposed to be lubed.  With a Teflon lining I think when it goes bad you are supposed to replace the cable.

Unless someone has a lubricant suitable with Teflon and drive shaft universal joints?  

[tvrla]

I believe only the control cables are teflon lined...but I could be wrong. It's easy enough to check. However, there are lubricants that are compatible with teflon - a speedo cable lube that's a dry graphite, and another one that also works for the teflon control cables, but forgot its name.

[Bob_Roller]

I've cleaned and lubed the speedometer drive cable on my '81 about 7 times in the last 29 years .

I take a plastic bag, cut the corner out of it put it over the cable conduit put a ty-wrap around it to get a somewhat leak proof seal, put some alcohol in the bag .

With the cable at the transmission end chucked into a drill motor, turn the drill motor on the alcohol will flow down and clean the interior of the conduit .

Do it a couple of times until it looks good to you .

I use a light air tool oil, do the same as the alcohol, but it gets a bit messy at the drill motor end when you use oil .

Don't use anything like WD40, it turns into a sticky varnish over time .

[R65Biker]

Great advice - will give it a try.
Thanks guys.

[Lucky_Lou]

The speedo cable is probebly the hardest working cable on the bike its not unusual to fail but the problem you describe is unlikely to be the cable usualy it will go "jumpy" then under read.More likely the speedo is the problem.
Lou

[Bengt_Phorqs]

At the risk of sounding sarcastic, I would equate the accuracy of a BMW speedometer, any BMW, to the accuracy of a sun dial.  You have at best only a general idea of your speed.  For what it costs to repair you're money ahead to use either a Vapor or a GPS.

[Justin B.]

The one on my RT-P is certified +/- 1 mph...  

[R65Biker]

Hi gents - I flushed the cable as per your recomendations. Too late and too cold to take it for a spin now. Will let you know if this sorted the jumping problem.
Cheers.

[montmil]

The one on my RT-P is certified +/- 1 mph...  

That ain't no Airhead.   Monte

[R65Biker]

Hi everybody - tested the "speedo cable service" this morning.
At about the same spot where it used to jump to max speed - it did so again. So that rules out the strange behaveour of the speedo. But something else happened - as it hit the max speed position (trip reset pin) - the needle completely broke off. I so wanted to take it for road worthy on Saturday...
Anybody flying into Johannesburg to bring a spare part with him?
What now - can it be fixed? Do I toss it and pay around 500 USD for a replacement unit?

[Barry]

Did the needle break in half or just pop off the spindle ? It might have been loose as they are just a push fit.  Either way it can probably be fixed by a specialist outfit if there is one in South Africa otherwise they do come up on ebay now and again. Airhead breakers should have them too.