speedometer 1982 124 spider

[smokey14]

when I hook up the cable to the trans and start the car the speedometer starts to read about 10 mph, the same as the tach. I just got the car back together from replacing the seals and gaskets so I had the motor and trans out of the car. any help will be appreciated.

[18Fiatsandcounting]

Maybe the car is just eager to get underway...?

But seriously, the speedometer drive is on the output of the transmission and only spins when the driveshaft is spinning. So, if the car is just sitting there, the driveshaft is not spinning, and I'm totally perplexed as to how the speedometer could be reading something. The speedometer is mechanical, not electric.

What happens when you drive the car?

-Bryan

[smokey14]

I am just putting the car back together after replacing all the seals and gaskets so it's up on jackstands right now. It's not in gear and I didn't fool with the trans, and when I remove the cable it stops. I am waiting for another part and will try running it sometime next week.

[18Fiatsandcounting]

Wait a minute, you didn't say the car was up on jackstands??? Then yes, if the rear wheels are off the ground, with the engine running, clutch engaged, and the transmission in neutral, there is enough friction in the gearing to slowly turn the driveshaft. If you look closely under these conditions, one or both of your rear wheels will be slowly turning. If the rear wheels are on the ground, this friction is not enough to cause the car to move, so the speedometer is motionless.

So, perfectly normal actually. If you put the brakes on while the speedometer is slowly inching upward, that will stop the driveshaft from turning and the speedometer should return to zero.

-Bryan

[smokey14]

Sorry, I misspoke the rear of the car has the tires on cinderblocks, the driveshaft is not connected and the car is not in gear. thanks for help

[18Fiatsandcounting]

Ahh, now I understand, thanks. Yes, if the driveshaft is disconnected, the transmission will spin slowly and perhaps erratically even when in neutral, enough to cause the speedometer to jump around a bit. Put the clutch in and the speedometer should return to zero.

-Bryan

[smokey14]

Thanks, I'm waiting for a gasket - oil leak and I will do as you said.