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> Jumpy tach
mittelmotor
post Jun 13 2012, 03:03 PM
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My tachometer needle tends to jump around a lot, rather than swinging in a nice smooth arc. Any suggested fix? If others have experience here, I'd love to hear how you've fixed it.

Thanks!
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brant
post Jun 13 2012, 03:04 PM
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do you still have points.
often its an ignition or points signal problem
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Black22
post Jun 13 2012, 03:10 PM
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I've have the same problem. Seems to be very common on our cars. I have a point-less system and it still bounces. I'll be watching his thread.
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SirAndy
post Jun 13 2012, 03:15 PM
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Several years ago, i bought a (brand new) relay board for unrelated reasons and one of the (many) things it fixed was my jumpy tach.

My guess is that on many cars the solder connections on the relay board are getting tired after 40+ years of abuse.
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mittelmotor
post Jun 13 2012, 03:25 PM
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Thanks! Car still has points. Now I have some areas to start the troubleshooting process.
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brant
post Jun 13 2012, 03:42 PM
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QUOTE(mittelmotor @ Jun 13 2012, 03:25 PM) *

Thanks! Car still has points. Now I have some areas to start the troubleshooting process.


on cars I have run points on....
I always notice an improvement when I reset dwell, clean up the points, and check the timing...

I noticed on cars with points that the tach would be bouncy and it would get slowly worse without me noticing.

worth checking your dwell and maybe replacing any worn points.
cheap enough to try

brant
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Bartlett 914
post Jun 13 2012, 04:03 PM
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You will find threads about changing capacitors in the tach. This may be a solution. I was under the impression that some dampening of the needle was done and may no longer be working correctly. Think grease or some such component. My tach was jumpy and nothing helped.
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914Bryan
post Jun 13 2012, 07:03 PM
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There were a lot of ideas here, I just learned to live with it and will fix another day. Check out this thread for possibilities:

http://www.914world.com/bbs2/index.php?sho...=148422&hl=

Good luck
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Series9
post Jun 14 2012, 09:13 AM
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QUOTE(brant @ Jun 13 2012, 05:42 PM) *

QUOTE(mittelmotor @ Jun 13 2012, 03:25 PM) *

Thanks! Car still has points. Now I have some areas to start the troubleshooting process.


on cars I have run points on....
I always notice an improvement when I reset dwell, clean up the points, and check the timing...

I noticed on cars with points that the tach would be bouncy and it would get slowly worse without me noticing.

worth checking your dwell and maybe replacing any worn points.
cheap enough to try

brant

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sean_v8_914
post Jun 14 2012, 09:19 AM
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always check teh cheap stuff first but...NH speedo told me that the damping fluid goes away after 40 years. they rebuilt my tach and it tracks solid now
but check teh easy cheap solutions first
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Valy
post Jun 14 2012, 12:44 PM
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I had the same problem in the past.
I took a plot of the points voltage with my scope.
The blue line is the actual voltage on the points and the red one is what you would like it to look like.
The biggest problem is that the negative spikes near the pulse middle cause the tach to believe the engine is spinning faster than it realy does. Some spikes are dumped by the tach filtering circuit but some are too big for it to handle so you see the tach jumping up.
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larss
post Jun 14 2012, 12:55 PM
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My tach got cured from jumping after fixing the earth wire inside the dizzy (that connects the plate to the body), the connection had come lose and I re soldered it.

Lars S
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hedgehog
post Jun 14 2012, 01:25 PM
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what i found when i had that problem was a loose coil wire....
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