Date:         Mon, 20 Nov 1995 12:14:00 -0800 (PST)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Maher, Steve (SD-MS)" <SMAHER@PO2.GI.COM>
Subject:      Re: Help: 89 Westy w/Noisy Speedometer


>Does anyone know a common failure/problem that would cause a speedo to
>click constantly while driving? (needle bounces also) Current mileage
>92,000. Should I replace(new/used), or tear into the speedo head?


Isn't this a pretty common problem, for all makes and models of cars,
also with a common solution?

I've always heard that, when a speedo cable is new, and you pull it out
of its sheathe and lay it down on a flat surface (table or whatever),
it springs out to a perfectly straight line.

But if you take an old one that's been in a car for a long time, and
do the same thing, its natural state is a curve-- probably in the shape
of the cable housing that's in your car.

Herein lies the problem. If you put that curved cable into its curved
housing, it snaps around to where its curve matches the housing's curve,
and lives happily ever after-- until you try to turn one end by driving
the car. remember that the cable is very flexible-- the ones I've seen
(many years ago) are just very long, tightly-wound springs.

If you turn one end just a little, say by pushing the car forward a few
feet, on a new cable the entire cable will turn that amount, since there
is nothing trying to hold it still. But for an old cable, it likes to
sit in that curved shape, and resists being turned, since the housing
around it doesn't turn, and essentially forces the cable to bend the
other way.

So, the wheel (or transmission for you new-car types) might turn one end
of the cable, as many as two or three times around, winding the "spring"
tighter and tighter, before the other end of the cable is finally
persuaded to leave its comfortable curved position. This end is connected
to the speedo, and suddenly snaps around, maybe two or three times (or
even more with its momentum), before settling back into the same old
curve. And the speedo thinks you have suddenly gone from 0 mph to about
200 mph in half a second, then back down to 0 a second later. And so
that's how it indicates-- bouncing up and down.

A bad speedo head could also do this, but I believe that most of the time
it's the cable that's the problem. I had a bouncing speedo in a '69 bus.
Replaced the cable only, and it was smooth as silk afterward.

Steve Maher   smaher@gi.com   '71 VW Transporter
                              '80 V6anagon soon