Tach & Speedo question

[blkfordsedan]

Replaced the factory L cluster with a tach unit I got off ebay last year. When the car is off and sitting still, the speedo needle sits about 1/4" below "0"; to the point where it is actually down into the temp gauge area. Consequently, the speedo is about 5mph slow.
The same situation with the tach needle. My guess is the tach is also off about 500rpm since at idle it shows 850rpm but is too slow. My instincts tell me someone removed the needles, probably to adjust the milage and re-installed them incorrectly. Can the needles be removed easily and set back to "0"? any ideas?

[mechanicaldj]

maybe the needle stops are missing

[GenevaDirt]

I believe if you are careful you can pull the speedo needle off and reset it. The tach needle is probably right...my car idles at 650-750.

Not sure if there are internal stops on the tach/speedo but there are none that are visible on any I have.

[b8kedbeans]

Yup, the needles can be pulled off and reseated. I removed mine to brighten them up with red fluorescent paint and reinstalled without any problems. One needle is longer than the other so make sure you don't mix 'em up when reinstalling.

Good luck!

[blkfordsedan]

The tach needle reads about 850@idle but it barely stays running at a warm idle. I would estimate the actual idle speed is only around 400-500, meaning the tach is off by about 400rpm (which is roughly the same amount below "0" that the needle rests at. I think I'll reset the speedo needle since I timed it and know it is 5mph slow. Then I can either hook up another tach to check the factory one or calculate the rpm @ 60mph based on gear ratio and tire size.

Question: Don't the needles work on magnetism? If so, would the starting point of the needle in reference to the gauge face have any effect on the gauge accuracy? (i.e. the speedo cable rpm is determined by the trans gear speed and has no direct mechanical connection to the needle). Also, does the needle readout have any effect on the odometer accuracy? Seems to me the odometer is a direct connection to the speedo cable.

[Biglay5150]

maybe the needle stops are missing

There are no needle stops.

[Biglay5150]

The tach needle reads about 850@idle but it barely stays running at a warm idle. I would estimate the actual idle speed is only around 400-500, meaning the tach is off by about 400rpm (which is roughly the same amount below "0" that the needle rests at. I think I'll reset the speedo needle since I timed it and know it is 5mph slow. Then I can either hook up another tach to check the factory one or calculate the rpm @ 60mph based on gear ratio and tire size.

Question: Don't the needles work on magnetism? If so, would the starting point of the needle in reference to the gauge face have any effect on the gauge accuracy? (i.e. the speedo cable rpm is determined by the trans gear speed and has no direct mechanical connection to the needle). Also, does the needle readout have any effect on the odometer accuracy? Seems to me the odometer is a direct connection to the speedo cable.

The needle being off will not effect the odometer. Just pop the needles off and set them at zero and everything should be accurate.