Bud:-
I think you may be expecting more from your tach than it is willing or
able to give. If you read the old road tests, one of the things they
always used to measure was the accuracy of the speedo. Why? Because
they were all significantly inaccurate, and they just wanted to tell the
car buyer by how much! Why don't you see that in modern road tests?
Because the instruments in today's cars are very accurate, or
insignificantly inaccurate.
Probably on the TD both the tach and speedo are accurate at one spot in
their range.
It's like my father always used to say, "Even a stopped clock is right
twice a day!"
David Littlefield
Houston, TX
On Thu, 12 Jun 1997 18:42:52 -0400 Bud Krueger <bkrueger@ici.net> writes:
>Sorry about bombing, but maybe some one has the answer. Checking out
>Lazarus' new 4.30 rear end showed up a nasty non-linearity in the
>tachometer reading. It's close, but reads a bit low at sub-1000rpm, is
>very close at 2000, reads 3500 at a true 3000, says about 4700 at a
>true
>4000. (I quit there, that's fast enough for the statistics).
> The non-linearity makes me feel quite certain that it's not a wrong
>ratio in the tach-drive gearbox. I opened it up last night and
>cleaned/degreased it. Stability improved, but not the error. When I
>had
>it apart I noticed that there is a bridge across the framework at the
>area where the face is attached by the two screws. The bridge consists
>of two pieces separated by a small gap with a hole concentric with the
>needle shaft. A small brass screw joins the two pieces. I'm guessing
>that this screw could function as a calibration tool. Anyone out there
>have any ideas on this?
>
> The non-linearity makes me wonder about the spring. I do recall
>from freshman physics that f=kx for linear springs. What's the
>function
>for quasi-planar springs? is the torque a linear function of the
>angular
>displacement? The pre-load on the spring can be varied by attaching
>the
>needle after different amounts of rotation. If I had a spare
>tachometer
>I'd start playing around, but right now I've got to make up for seven
>weeks of not having my lbc fix.
>
>Any and all help, advice, or sympathy will be welcome. (Even TS will
>be
>accepted.)
>
>Bud Krueger
>52 TD "on the Road Again"
>
>
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