my speedometer does not work on my 1986 560sl.(R107) not sure if its the gears or the speed sensor on the trans. how do i test to see if its the speed sensor. plus where is the sensor located?

I am guessing it uses the ABS wheel speed sensors. Judging from the videos on YouTube, the speedometer itself is more likely the problem. I am not an expert on those however, but you might watch a video and see if that sounds like the problem you are having.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

No, it doesn't use the ABS sensors. It uses a sending unit in the tailpiece of the transmission. The speedo is electronic, there are no "gears" other than for the odometer portion of it. How are the rest of the gauges and indicators in the cluster?

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'11 Honda Accord EX - "The Daily" 70K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "Diseasel Jr." 173K
'94 BMW 525i - "The Red Car" 180k

thanks for the replies. the problem lies with the speedometer and odometer. everything else works fine. i was hoping it wasnt the gears inside the speedometer , but it seems to keep pointing to that direction since these cars are notorious for the gears wearing down over time. car has 125,000 miles . i was hoping it was an easier fix , rather than taking apart the dash . i guess i was hoping there was a way to test the sensor to see if it was bad