Impalas.net banner
1 - 7 of 7 Posts

·
Registered
68 Impala SS convertible
Joined
·
15 Posts
Discussion Starter · #1 ·
I have a 68 Impala SS with a 327/400 auto combo. 225/70/15 tires. Passing a few radar signs, it appears that my Speedo is 6-7 mph slower than reality. Any suggestions on how to recalibrate it? Thx.
Steve
 

·
Registered
Joined
·
1,136 Posts
I have a 68 Impala SS with a 327/400 auto combo. 225/70/15 tires. Passing a few radar signs, it appears that my Speedo is 6-7 mph slower than reality. Any suggestions on how to recalibrate it? Thx.
Steve
There is no calibration, what throws off the reading is the difference in the mated components compared to the Speedometer gear. These plastic gears are readily available. If your car came with the 327/400 you need to find out what tires came with the car. The tire size will throw off the reading. Then you have to find the equivalent of the metric tires size to the original and find the correct gear for those tires and 327/400 combination. May be in th service manual or possibly the GM heritage Kit: https://www.gmheritagecenter.com/do...rmation-kits/Impala/1968-Chevrolet-Impala.pdf

Paul
 

·
Registered
Joined
·
1,136 Posts
I believe the original size was G70 15. The 225/70/15 I have on there are probably not tall enough.
Than you have to find the 68 equivalent of what you have on there and see what gear that combination used
 

·
Registered
Joined
·
24 Posts
My '61 Bel Air with a Muncie 4 speed had a 21 teeth gear that was off about 10mph (forget exact mph) but I calculated that a 17 teeth would bring it close to actual mph and it's dead on. Just sharing.
 

·
Registered
Joined
·
85 Posts

·
Super Moderator
Joined
·
1,620 Posts
And then, once you know the original size, you use a tire comparison site to match the old size to what you have now (and what you might need to correct that error).

 
1 - 7 of 7 Posts
Top