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Speedometer reading almost twice as fast


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#1 Sl1m1

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Posted 19 August 2018 - 04:40 PM

Bought the car and speedometer wasn't working. Did into it and found that the car had a 17 tooth Auto gear in it. (Car is a manual). Replaced the assembly with a 23 tooth gear assembly. Speedometer works now but it reads out almost twice as fast as the car is really going.

Any ideas?





#2 mikec

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Posted 19 August 2018 - 05:03 PM

Is the odometer accurate?  If so, odds are the internals of the speedometer are full of transmission oil.  There is a seal on the transmission end of the speedometer cable and speed pick-up assembly (which is used by other things on the car)...  when that seal fails transmission oil wicks up the speedometer cable.  That oil fills up very small clearances in the speedometer assembly throwing off its accuracy.  The odometer though is driven by the cable directly so the transmission oil doesn't affect it.

To fix: replace the speedometer pickup gasket.  then remove the cover over the instrument panel (2 screws above the clear plastic, one in the bottom of each switch pod).  Remove the instrument panel screws, reach around behind it and unclip the speedometer cable.  Then undo the wiring harness connectors.  You'll have to eyeball the assembly to see how to pop the clips off to open it (watch the trip odometer reset button - don't bust it off.  Unscrew it first).  Remove the fasteners holding the speedometer assembly.  Use spray brake or carb cleaner to wash out the guts.  Do NOT touch nor get spray on the face of the guage - it damages/scratches easily.  You'll also see a small glass tube on the back of the assembly - that's a magnetically activated switch for the cruise control.  The brown ring below it has several magnets in it; don't damage either piece.  Looking inside the gauge guts, you'll see a circular part a little larger than a quarter... it's a few small pieces and there is a very thin spiral spring there too.  That spring is critical - and fragile.  Dribble (don't spray) the carb/brake cleaner in this area.  Get those circular parts totally clean though - especially the thin gap between them.  Then drain the speedometer cable too.

mike c.

#3 Sl1m1

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Posted 20 August 2018 - 07:26 PM

Thank you for the thorough explanation Mike! Sounds like you have experience with this issue. I will take a look.

Appreciate it!

#4 Bradrock

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Posted 20 August 2018 - 07:27 PM

Sounds like a fun project..............................NOT. :)
Run's with scizzor's




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