Rear end change and speedometer effect
#1
Rear end change and speedometer effect
I have a 69 Cutlass that a previous owner did a lot of changes to. He put in a 455 and judging by the high rpms a=it seem he swapped out the rear end as well. At 60 mph my speedometer reads 75-80. It is a real gas guzzler and I am not concerned about setting track times. I haven't had a chance to pull the rear end cover and count teeth to see what I have. I may well put it back to original but for the meantime would like to have a accurate speedometer. Can I change the speedometer gear to correct this issue?
thanks,
Steve
thanks,
Steve
#2
Yes Steve you sure can. You'll likely be changing both the drive gear and driven gear, depending on which housing you currently have. If you're lucky, you'll only be swapping the driven gear but you have pretty big spread of inaccuracy. Don't forget to do the proper math.
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
#7
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
Too much error that way. 10 turns of the tire is better to determine accurate driveshaft revolutions. Too easy to mistake 3.08, 3.23, 3.42 doing only one revolution. but with 10, it's easy. Sounds like the rear is closer to a 3.91 or 4.33 though. Standard rear end on that car should be either 2.56 or 2.78
#8
Yes Steve you sure can. You'll likely be changing both the drive gear and driven gear, depending on which housing you currently have. If you're lucky, you'll only be swapping the driven gear but you have pretty big spread of inaccuracy. Don't forget to do the proper math.
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
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