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Author Topic: Bouncy speedo needle  (Read 2513 times)

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Offline SG103

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Bouncy speedo needle
« on: July 09, 2017, 04:30:27 AM »
Hi,
I recently bought a 1975 CB750F. I've been pleasantly surprised at how well works with only a complete carburetor cleaning. However my speedometer needle seems to be constantly bouncing, maybe 2 to 4 mph each way, is this normal?
By the way, this forum is AWSOME.
Thanks,
Arnold
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Offline Bodi

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Re: Bouncy speedo needle
« Reply #1 on: July 09, 2017, 05:32:01 AM »
Usually a speedo drive cable that needs lube or is damaged. A kink or rusty spot can grab, the cable core is somewhat springy... the effect slows then speeds up ghe speedo end every turn. Remove and inspect the cable for kinks and that thdcore turns freely. The core can pull out from one end for insoection and cleaning I think, should be oily and dirty but no kinks. New cables are not too costly.
Could be internal to the speedo of course, not as likely. I suggest not trying to fix that yourself...
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Offline TwoTired

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Re: Bouncy speedo needle
« Reply #2 on: July 09, 2017, 11:31:36 AM »
+1 on cable lube and ensuring no kinks.  Do extract the inner cable and inspect for tight spot wear or kinks.  See if you can find "speedometer cable lube" at the parts store.  There's a good reason for this "specialty lube".

The speedometer needle attaches to a ferrous bell.  The cable ties to a sectioned bell that has magnets.  As the cable turns, the magnet pulls on the bell which deflects the needle.

If the gauge bearings wear out from old stale lube, the two bells can come in contact and that makes the needle deflect irregularly from friction contact.

Taking apart the speedometer is not for the timid, or neophyte.  Easy to mess things up inside and replacement internal parts are not readily available.
But, if you have more prowess than the norm, go for it!

If a refurbished or new cable doesn't correct the needle bounce, getting another gauge is the easiest option.

Cheers,
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Offline Don R

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Re: Bouncy speedo needle
« Reply #3 on: July 09, 2017, 12:01:11 PM »
 Thanks for that info TT. I put on a temporary speedo while changing to new faces and the needle promptly jumped until it came off the pin. The original one worked fine, I wondered why. I bought a few bikes with damaged gauges so I have a few to practice on.
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Offline SG103

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Re: Bouncy speedo needle
« Reply #4 on: July 10, 2017, 03:49:02 AM »
Thank you for the replies. I took the speedo cable out of it's sleeve, no kinks, a bit of caked grease at drive end. Overall it looked pretty good, will try and get speedo cable grease, but problem still persist after cleaning and replacing.
Arnold
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Offline flybox1

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Re: Bouncy speedo needle
« Reply #5 on: July 10, 2017, 07:13:32 AM »
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Offline Tusong200

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Re: Bouncy speedo needle
« Reply #6 on: July 17, 2017, 06:42:16 AM »
I had a very sluggish speedo  on a 350F that I recently purchased. It hadn't run for many years. I c leaned out and lubed the cable but this didn't help. I was concerned and thought that I'd have to get a different speedo or send it out for fefurb.

However, after I put a couple of hundred miles on the bike the speedo came back to life!! Works just fine now.
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Offline Bankerdanny

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Re: Bouncy speedo needle
« Reply #7 on: July 17, 2017, 07:11:30 AM »
Quote from: Tusong200 on July 17, 2017, 06:42:16 AM
I had a very sluggish speedo  on a 350F that I recently purchased. It hadn't run for many years. I c leaned out and lubed the cable but this didn't help. I was concerned and thought that I'd have to get a different speedo or send it out for fefurb.

However, after I put a couple of hundred miles on the bike the speedo came back to life!! Works just fine now.

+1 sometimes they just need some mileage on them to work out the dust and corrosion that can accumulate while sitting. This probably isn't the most common solution, but, after lubing the cable (personally I have always just used wheel bearing grease on mine) I would get the bike out and put some miles on it and see if it clears up on its own.
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Offline Deltarider

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Re: Bouncy speedo needle
« Reply #8 on: July 18, 2017, 03:05:32 AM »
Without having read the previous posts (I apologize), here's what helped me. Decades ago I had bouncing needles (both speedo- as well tachometer). I removed the inner from the outer cables, inspected them for damage (there was none), cleaned them and lubed them with lithium grease before assembly. Never had a problem no more.
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Offline SG103

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Bouncy needle fixed
« Reply #9 on: July 19, 2017, 03:37:15 AM »
Bouncy speedo fixed. I took my cable out again and rubbed a bit of synthetic brake grease on the cable and it's great now. There was so much difference in the way it works I have a hard time believing it was just the grease, maybe it wasn't in right.
Thanks again everyone.
Arnold
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