1990 Chevy Lumina Speedometer Too Fast

1990 CHEVROLET TRUCK
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KAINAIGUY
  • MEMBER
  • 1 POST
Recently had a used transminssion installed into my 90 chevy lumina car. Now my speedometer says i am going about 20-30km/h faster than i am actually going...Any suggestions what the cause is?
Mar 4, 2006 at 4:54 AM
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BURRBRIAN
  • ✓Experienced Mechanic
  • 158 POSTS
Howdy, a couple things to consider would be the gear ratios. If the gears are a different ratio from one tranny to the other this could throw off your readings. Also if you have changed the rear tires and went a different size, say p245 to a p265 profile this would change your readings.Just a couple of possibles to look into. I think you will find that something along these lines is what is happening.
I'm not an expert but have run into similar problems,
Best of luck and watch for radar. :!:
Mar 6, 2006 at 12:07 AM
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Suggested Repair

Compare the replacement transmission gear ratio with the original, and confirm tire size has not changed. Either a different ratio or a larger tire diameter can make the speedometer read high.

Conversation Summary

After a used transmission was installed in a 1990 Chevy Lumina, the speedometer read about 20-30 km/h faster than actual speed. The reply suggested a different transmission gear ratio or a change in rear tire size as likely causes and advised checking those.

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