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I just replaced a speedometer cable and came across the speedometer transducer. I was curious why a transducer is needed in the system when the speedometer is mechanically driven. There is no cruise control, the speedometer is not digital, and I can not see any other reason that the mechanical input would need to be converted to an electrical output. Does anyone know what it is used for? Thanks, Mark
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Re: 75 Corvette speedometer question
Mark-----
You didn't mention where you found this device. There is no transducer that I am aware of used in a 1975 Corvette speedometer system. If you referring to the device which is mounted on your transmission speedometer output fitting and to which the speedometer cable then attaches, that device is a speedometer ADAPTER which is used to provide an accurate output speed given the installed speedometer gearset and rear axle ratio. Many 70+ Corvettes were originally fitted with speedometer adapters, depending upon rear axle ratio, in order for GM to more "standardize" transmissions used at the assembly plants. Earlier there were a variety of different transmission part numbers, but the transmissions mainly differred only with respect to the installed speedometer gear set. Multiply M-20/M-21/M-22 variants by the necessary speedometer gear sets depending upon rear axle ratio and you see why this method was instituted.
The speedometer adapter is a geared device which modifies the output of the speedometer driven gear by a fixed percentage. Usually, they are in the .9 to 1.1 range and the exact ratio is often stamped on the unit.
However, notwithstanding the above, I'm still curious if this is the device that you're talking about. You mention converting mechanical speedometer output to an electrical output. There are no wires whatsoever connected to the speedometer adapter making it impossible for this device to be construed as a transducer, so perhaps, you are referring to something else. Please advise with a better description of the device.In Appreciation of John Hinckley -
Re: 75 Corvette speedometer question
Mark, transducer's are found on 77-82 Corvettes with cruise control. No others unless someone added it to your car as an aftermarket kit etc.Comment
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Re: 75 Corvette speedometer question
Thanks Joe, It must be the speedometer adapter that you mention because I can't find any other equipment to suggest it was an after market add-on of a cruise control. MarkComment
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