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Speedo Recalibration


Super Jamie

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It just so happenes that i was discussing this with Peter Robinson on Saturday.

"GM Instruments" trading as "Automotive Instrument Repairs".

59c Glenvale Cres

Mulgrave, VIC 3170

Ph.(03) 9561 2366

Fax (03) 9561 9134

 

Auto Instrument Repairs

 

They manufacture a box that contains replaceable gears. The box is fitted to the back of your speedo and then the the speedo cable plugs into the box.

By changing the internal gears within the box, they are able to adjust the rpm's of the speedo cable to correct it back to the proper reading.

They drive the car and test the real speed of the car with GPS or something along those lines and then simply swap gears to adjust your speedo reading.

 

This product can be used to compensate for not only varied rolling diameters of aftermarket wheels, but also to compensate for different diff ratio's.

The product is a bit pricy at $250. I don't know what speeding fines cost (never had one), but i would imagine thats roughly 2 speeding fines there.

 

I realise this place is not practical for you, but its worth a call to see if they have stores near you, or know of anyone that manufactures a similar product up your way.

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"Recalibration

When a mechanical speedometer is suspected of being inaccurate, Beale Instruments check it against a Smiths Speedometer Calibration machine.

 

If the speedo does come up with a false reading, it is either partially magnetised or de-magnetised accordingly. For example, to trim downwards the speedo's indicated speed, the magnets at the back of the gauge are moved up against a de-magnetising block built into the calibration machine. This reduces the amount of magnetism on the gauge's main shaft, and the needle therefore doesn't travel as far."

 

" If the speedo unit itself is functioning accurately but you've altered the car's overall gearing (diff ratio or wheel diameter), you need a ratio box. The first step is to drive the car with a pulse counter plugged in to measure the number of speedo shaft revolutions over a measured distance (say, one kilometre). This number is then cross-referenced on a special chart and the right gear for the job is chosen from the list. It's then just a matter of putting the right gear set into the small ratio box housing and installing it to the cable between the gearbox and the speedometer input. These mechanical ratio boxes generally cost around $110 retail."

 

"Contact:

Beale Instruments

+61 8 8445 6644

 

[email protected]"

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does anyone know a place that will recalibrate a mechanical speedometer?

Hey jamie you could make custom guages to suit your wheels - reposition the markers ;)

 

intead of like on your tacho "x1000"

 

Speedo can say "@235/45/17"

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