sredmyer Posted November 11, 2017 Share Posted November 11, 2017 So I just bought another 70 SS454 which had the rear gears changed to 3:55s. While I like this gear a lot for local cruising (and tire spinning of course) it is not so good on the freeway. That said, I think I will leave it as is at least for now. Can anyone tell me if I can simply change the speedo gear in the transmission to correct the speedometer...it is currently reading about 90 MPH when doing 70 on the freeway. Quote Link to comment Share on other sites More sharing options...
stangeba Posted November 11, 2017 Share Posted November 11, 2017 I think so. Here is a web site that may help. https://transmissioncenter.net/product-tag/speedometer-gears/ Quote Link to comment Share on other sites More sharing options...
72-CLASSIC_RIDE Posted November 12, 2017 Share Posted November 12, 2017 Here is another Calculator Tool to help you . If you know what your Drive & Driven gears in Transmission are, it will help in deciding what course of action to take. I had the same issue when I replaced the Rear End & gears to 331:1 ratio 12 Bolt Posi from a 273:1 ratio 10 Bolt if I remember right. I ended up putting a Gear Reduction devise between speedo cable at Tranny connected to devise and to Transmission. Damned if I can remember what the Technical name is. I was way off and brought actual speed within 1% of accuracy. Pretty sure you will get a lot of help on this. http://www.tciauto.com/tc/speedometer-gear-calculator/ Doug 1 Quote Link to comment Share on other sites More sharing options...
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