There IS another way!
Before we get enamored of custom electronic designs, I faced the exact
same issue trying to match a Porsche 180 MPH speedo to my Custom Built
car (pictures in my article on TigersUnited.com) and found the perfect
solution. Trucks are commonly running into this calibration situation,
and a simple mechanical device has been designed to do this job.
The turns/mile of the transmission output cable are measured, and the
turns/mile of the speedo are either known or measured. Most American
units are 1,000 turns per mile, but for best accuracy this is measured
on a simple bench test.
A small case, containing some gears, a cover, and two speedo cable
connections is fitted with the correct set of gears that reduce/enhance
the output turns to correct the input turns to match what output is
required. This fits in line with a two piece speedo cable, usually
fabricated by cutting and putting the proper ends on your original
cable. Results are dead accurate, if you did the homework correctly.
Best of all, that cover is field removable, and a new set of internal
correction gears can be installed quickly, if a change in tire size is
made.
No speedo work is necessary at all, as long as it is in good shape, and
it's calibration is correctly known. Notice: due to age and loss of
magnetism, the speedometer and the odometer may not agree, and the
speedometer's magnetic field must be fixed by a speedo shop. Easy job.
Had this device for 17 years, and it still works fine.
See professional speedo shop that works on trucks.
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
http://www.TigersUnited.com/gallery/SteveLaifman.asp
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