Author Topic: Tachometer Unstable  (Read 674 times)

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Offline grumpy56

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Tachometer Unstable
« on: September 25, 2024, 03:53:18 PM »
OEM tachometer works perfectly under 7K. Steady as a rock. However, at or above 7K or so, it bounces around like a madman in a padded room. Any ideas? Thanks.

Offline newday777

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Re: Tachometer Unstable
« Reply #1 on: September 25, 2024, 05:49:04 PM »
There is a bell around the needle shaft in the tach, that bell is filled with oil to dampen the bounce. When oil leaks out the bounce happens.
There are some posts on refilling it.
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Offline grumpy56

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Re: Tachometer Unstable
« Reply #2 on: September 25, 2024, 07:09:00 PM »
Thank you. Will check it out.

Online scottly

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Re: Tachometer Unstable
« Reply #3 on: September 25, 2024, 07:16:37 PM »
Since it's steady as a rock up to 7K, the damper is probably not the issue. ;)
The first thing I would check is the drive cable: if the inner cable is dry or kinked and binding, it can wind up like a spring, making the needle drop, then suddenly breaking loose and unwinding, making the needle jump.
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Online CycleRanger

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Re: Tachometer Unstable
« Reply #4 on: September 25, 2024, 08:57:08 PM »
Since it's steady as a rock up to 7K, the damper is probably not the issue. ;)
The first thing I would check is the drive cable: if the inner cable is dry or kinked and binding, it can wind up like a spring, making the needle drop, then suddenly breaking loose and unwinding, making the needle jump.

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Offline Deltarider

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Re: Tachometer Unstable
« Reply #5 on: September 26, 2024, 12:14:49 AM »
A long time ago, I took out the inner cables (both speedo and tacho), cleaned them with some kerosene and lubed them with lithium grease. Never had to do it again. Bike has done 100.000km since.
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Offline pjlogue

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Re: Tachometer Unstable
« Reply #6 on: September 26, 2024, 06:22:21 PM »
I would also add to the above, once the inner cable is cleaned, is to flush the sheath the cable runs in with kerosene.  Hang it to dry for a day then lube the inside with a good lithium grease or chain lube.  Then grease the inner cable with the same grease and put it back together.  If the cable or sheath has been bent so it got kinked the above won't work. 

-P.

Offline fire113

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Re: Tachometer Unstable
« Reply #7 on: September 28, 2024, 05:06:27 AM »
OEM tachometer works perfectly under 7K. Steady as a rock. However, at or above 7K or so, it bounces around like a madman in a padded room. Any ideas? Thanks.

What CB bike (Modell/Year) do You have there ?
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Offline grumpy56

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Re: Tachometer Unstable
« Reply #8 on: September 30, 2024, 07:13:07 AM »
 I have a 76 CB400F with about 6.5K miles. Will clean and lube my cable first. Thanks all

Offline HondaMan

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Re: Tachometer Unstable
« Reply #9 on: September 30, 2024, 12:58:18 PM »
If the bike is a 750K0-K6 model, parking it for long periods (like winter) with the steering turned fully to the right side can make the cable for the tach unhappy. It then takes about 1000 miles for the needle to settle back down, provided the bike isn't parked in that position every night after a ride. Mine reminds me of this often...
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Offline grumpy56

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Re: Tachometer Unstable
« Reply #10 on: October 01, 2024, 06:43:51 PM »
Cleaned and lubed the sheathing and cable and re-attached. Didn't test it at high revs yet. Did strip the screw holding the cable in the valve cover. Used a Dremel to cut a slot in the head of the screw and it came out pretty easy with one whack from an impact driver.