Speedometer Problem

I don't really want to start a new thread here. But I think I've looked pretty closely and don't see one that addresses my problem. I apologize if I've missed something. Speedometer always bounced a bit, but today it really started bouncing and than wouldn't recover after slowing my speed. It progressively went downward and pretty much finished at about 10 mph, quite erratic. The only thing that I did different today was that I was polishing the back wheel hub and occasionally the buffer wheel (using a drill) would come in contact with the speedo drive (lightly but made contact). Not sure how that could have caused the problem.

What I'm really wondering is will I cause damage to the instrument or other issues if I ride it until I get around to fixing it. If so, should I disconnect the cable from the speedo drive or speedometer? The speedometer is the original Smiths and is still quite nice. I really don't want to restrict my riding because of a speedometer other than the ability to have an accurate odometer and the weather here in New Hampshire is getting very nice.

For me the bouncing speedo stemmed from the drive and or cable. The first and easiest thing is to clean and lube the cable. Second and a little more involve is clean and lube the drive. Might as well do both. If a new drive is needed, stay away from used. I think people try to re-coop losses when they buy a new and I get stuck with another bad one. New ones are rather handsome. My issues with the speedo is its tendancy to run high down the highway. +20 mph sometimes. That one will cost me some jingle cause I ain't goin in there!
I think running with just the tach is more grassroots anyhow. I tent to watch that more.

hi jim,first off i would suspect the cable,disconect it at both ends and see if it turns freely with fingers,if not try lubing it and try again, make sure any curves in it are as smooth as possible,if all is ok you can then test the speedo with an electric drill conected to the drive end of the cable{cordless with reverse is best cos i cant remember which way it turns}

chris plant said:

hi jim,first off i would suspect the cable,disconect it at both ends and see if it turns freely with fingers,if not try lubing it and try again, make sure any curves in it are as smooth as possible,if all is ok you can then test the speedo with an electric drill conected to the drive end of the cable{cordless with reverse is best cos i cant remember which way it turns}

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Not sure what to use for lube. Should I just spray a little lithium lube into the cable? Silicone? Both easy to do.

I think any regular grease is ok, pull the inner part out, clean it & lightly coat it as you slide it back in but remember NOT to grease the last 6 inches at the top by the Speedo. I've was told long ago that the grease is not to be allowed to get in the Speedo for some reason. Good luck.

Lubricated the cable - it was bone dry - probably not a big surprise after 36 years. Didn't solve the problem. Disconnected the cable from the drive and turned it with my drill. Speedometer worked properly. Looks like a bad drive.

Could be that the square ends on the cable could be rounding off & not driving properly in either end. Common problem.

Flo said:

Could be that the square ends on the cable could be rounding off & not driving properly in either end. Common problem.

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Not on the speedometer end since it drove cleanly when using the drill. Is the rounding noticeable? The drive end looked square but than again I wasn't looking for that.

JimR said:

Flo said:

Could be that the square ends on the cable could be rounding off & not driving properly in either end. Common problem.

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Not on the speedometer end since it drove cleanly when using the drill. Is the rounding noticeable? The drive end looked square but than again I wasn't looking for that.

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I had to replace my speedo drive a year ago. I had ridden up to Nortona and back on a one day deal, and when I reached Jupiter on my way home, I noticed the Speedometer was bounced between 50-70, though I knew I was going just over 80. by the time I reached Pompano Beach, the Speedometer was reading 10-30. Once off I-95, an occasional blip was all it would do. Drill check showed the gauge worked fine. Replaced the drive with the Emgo part (about $75) the next day, and no issues since.

Though I re-greased the original unit, I did not take it apart. I suspect sitting for 25 years without spinning had something to do with its early demise. Though I had put about 1500 miles on the original unit, doing 600 in one day probably killed it.

Got the new speedo from Old Britts this week. Don't have a whole lot of time so I figured I'd ask for some help. Looking at the blowup of the rear wheel assembly it seems like I can just remove the portion of the axle on the side with the speedo and put the new speedo on without removing the wheel or the rest of the assembly. Seems like it would be a 30 min. job. Anything I should know or worry about?

I assume you are talking about the speedo gearbox on the rear wheel. Make sure the assembly does not touch or rub on the rear wheel hub cover. If it does, it has a tendency to drag the gearbox around and mess up everything. There is a top hat spacer (item 34 on OB rear wheel assembly) that usually needs replacing to keep the gearbox from rubbing. There are a couple of threads to this issue.

Dave
69S

Check the length of the cable protruding beyond the outer casing of the cable and into the speedo. It should stick out no more than 7/16 inch. If more, it can ruin the instrument. A few of the aftermarket speedo cables I have purchased have been too long and needed to be shortened. Also check your speedo drive. It may be in need of some attention.

Hey Jim,
I have had this problem with a new oiled cable and I fixed it when I made sure the speedo hub cable outlet is perfectly horizontal.
If the outlet points down the speedo bounces around like a fat tart on a trampoline!

Good Luck

Jim,
I had the same problem a couple of years ago after fitting a new cable. I found the cable length was a little short and was migrating out of the speedo drive. I solved this by fitting a small spacer.

Cash

Make sure the speedo drive tabs engage the two notches on the lockring on the hub. Carefully rotate the drive until you feel the tangs engage - it will slip in towards the hub maybe an 1/8 of an inch. Once home, rotate the drive so it lines up nice and straight with the cable, re-fit the spacer and axle.