Here's two options for repairing
your speedometer: Do It Yourself.........PDF file link at the
bottom of the page OR follow the steps below and send your
speedometer out for repair.
Between the new Toyota
transmission gearing, the new Nissan 4.08:1 differential and
lower profile tires my speedometer was way off both with regard
to speed and distance covered. Fortunately Herman addresses this
by including what you need to do before sending your speedometer
out for recalibration.
I had noticed in the past that
there's a number on the bottom center of the Smith speedometer
face. It might be 1200 or 1120 or, in my case, 1000. This number
represents how many times the speedometer cable will turn one
mile (5280). When you start changing things like tire size or
diff gearing the cable will end up turning more or less than the
required turns to be accurate.
So what you need to do is remove
the speedometer from the car so you can watch the cable turn as
you drive. Put piece of tape on a flat side of the cable so you
can count revolutions. Now all you need to do is drive exactly
one mile and count 1000 times! Ok.... that won't work so how
about measuring off exactly 1/100th of a mile or 52 feet 9-1/2
Here's the steps:
- Remove your speedometer.
- Put a piece of tape on a flat
side of the speedometer cable.
- Mark off exactly 52 feet
9-1/2 inches on the pavement.
- Have a friend watching your
rear tire to tell you when to stop.
- Park your car with the rear
tire centered on the start mark.
- Drive toward the finish mark,
counting the times the cable revolves.
- Stop the car when your rear
tire is centered over the finish mark. That's your friend's
- Record the number of turns
including your best estimate of the last fraction of a turn.
- Do this about 4 or 5 times
and use the two results that most closely match.
In my case the cable was turning
about 11-3/4 times. The speedometer number on the face was 1000
which divided by 100 (we were doing 1/100th of a mile) equals
10. To be accurate my cable should have been turning 10 times in
the measured distance.
So now all you have to do is go to
the speedometer repair shop of your choice with your speedometer
and cable and tell them how many turns the cable made in 52 feet
9-1/2 inches. If they look at you like you have two heads, pick
up your speedometer and head to a shop that understands Smith
I used West Valley Auto in Reseda, Calif which specializes in British cars.
Their phone number is 818-758-9500 and ask for Morris.
They did a great job rebuilding the speedometer, including new
gearing for the odometer and a new inner cable. And turned it
around in about 10 days.
Since then I've had then calibrate
my tach and this winter (2012-2013), I'm thinking about a total
gauge refurbishing right down to a re-paint of all the
faces in black letters/numbers on white face. They do great
The proper cable is key to an
accurate and long lasting gauge as the wrong cable specs can
damage the internal workings of the gauge. When I spoke to
Morris he asked me to measure the tip of the cable and then told
me it was 1/16" too long. He explained that basically a
cable tip that's too long or thin/fat can damage the inner
workings of the gauge.
So here's the specs that Morris requires:
1. The minimum tip protrusion is 1/4" and the maximum is 5/16"
2. The tip should be square and measure a minimum of .122"
square to .124" square
3. He prefers that the cable bushing be nylon and not steel.
If your cable doesn't meet those
specs have the cable rebuilt to the specs. It will only cost
And don't assume that the new
cable you just bought from Moss or TRF has the proper
specs..........measure it and confirm that it's correct.
If you want to try and rebuild the
speedometer yourself, you can
download this PDF file.