I've done a lot of work on my BJ8's speedometer--the tach is basically a
speedometer without the gearing for the
odometer and trip meter.
You can go through the tach yourself. There is no mystery--the cable rotates a
magnet which causes a flanged flat disk
to turn ('magnetic coupling') which moves the needle. There are no ball or
roller bearings to be concerned about; the
cable drives a small shaft--which kinda looks like a little camshaft--to turn
the magnet. There is a small watch spring
to return the needle to zero. Probably what's happened is whatever lubricant
was on the small shaft has dried out and
impeded the needle and plate from turning. Worst case is the old/misrouted
cable damaged or wore out something.
You'll need a jeweler's screwdriver kit ($5-10). Get a clean workbench and I
lay down paper towels to keep small bits
from escaping. The Anthony Rhodes 'white paper' on speedometers that's been
around forever might be helpful. I use
'electronic circuit cleaner' to clean the parts; DO NOT use 'electrical parts
cleaner;' it's too harsh. I use a light
lithium grease to lubricate the shaft.
If anything's busted and you can't find the part then you can button it back up
and send it out for service (I'm
guessing about $100-200 plus shipping, etc.).
Bob
On 4/19/2012 1:11 AM, Derek Job wrote:
> Hi all
>
> Have an issue with the tacho on the car I'm selling. When I bought the car
> 2 years ago the tacho was working fine. I didn't get to spend much time
> with the car but when I finally did I noticed the tacho cable was wrongly
> routed which made it very tight and possibly stretching it. I re-routed the
> cable and it was working fine.
>
> About two months ago when I got the car to my house I noticed it was
> sticking at 2000 revs sometimes at 3000, anyway not moving freely. I
> checked all connections, lubricated and I tested it using a drill attached
> the cable but that procedure never got it to move even a tiny bit. When I
> reconnected it to the engine it did at least move but got stuck again.
> Decided to buy a new cable assuming old one might have been damaged with
> stretching etc. Connected it yesterday and nothing, not even the tiniest
> movement. At least it moved with the old cable.
>
> Any ideas? Is it time the tacho was serviced?
>
> cheers
>
> Derek
>
>
>
--
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Bob Spidell San Jose, CA bspidell at comcast.net
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