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Speedo mis reading

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Stuartm:
Hi guys,

My speedo is under reading. I spoke to the guy at banks and he said to re calibrate it by pushing the car so the wheels turn round 6 times and count how many time the speedo cable spins. As anyone heard of this. How do you the calibrate it ?

Thanks in advance

Stuart

EuropaTC:
Hi Stuart,

I'm not going to be much help here because I've got to admit I didn't know you could re-calibrate a speedo, or at least not without changing either the cable drive wheels at the gearbox end or the internals of the speedo itself.  I thought the speedo's had the turns per mile figure on the dial and that was matched to the gearbox at manufacture, so in essence it's a fit and forget thing. Changing the gearbox or overall wheel diameter will mess this up, a dry/worn cable or oil/grease inside the speedo head can cause it to flicker about, but assuming your car is standard there shouldn't be a problem with the gearing per se.

How much is it out ? A constant number or does it become less accurate as speeds rise ?  The other question is how do you know it's out - I'll assume it's not because you've just gone through a speed camera at 30 and been given a ticket for 50  :)   

Brian

cal44:
Stuart,
could be any number of things wrong.  I send my stuff out to the pros as I don't know how (nor do I care to learn). 
One of the gear teeth could be broken, needs a good cleaning and oiling, the gears are plain worn out.  Most are plastic/nylon.

I sent my last set of gauges from a 356 to the guys in Hollywood.  For the life of me could not figure out how the chrome trim ring came off.  It came back looking like new and all worked perfect. 

Look at it like a wind up watch.......I don't know how to do those either.
 mike

Stuartm:
Thanks for the replies.

The speedo reads low and progressively gets worst with speed. Checked it against gps. I will check all that has been mentioned and put a new cable in. Otherwise I will send it off to someone.

Thanks again

Stuart

EuropaTC:
Hi Stuart,

My money is on  the cable, either sticking or having a sharp bend somewhere. My car is on it's 3rd cable and I really do try hard but they seem to have a finite life. But if you have to remove the speedo I'd be very tempted to take a peek inside and give it a clean because if you're resigned to send it away for overhaul you don't have much to lose, do you ?

Let's know how it works out.

Brian

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