Might sound like a goofy question... But I just replaced ( Finally!!! ) the spedo in my 57 Wagon.. THANKS HELLFISH! ! ! The first one started going haywire on the way to indy a couple years back, and we just disconnected it while flying down the highway. It looked like the original spedo so I just figured it was bad from when I bought the car. I just got the brand new one in, and took it around the block.. About 25 mph it was showing around 60,, maybe 35 it was showing 90.... The car originally came with the 283 and a powerglide, now has the 350/TH400 combo.. IS the spedo drive on the TH400 a different ratio than the Powerglide? Can I get an adapter gear that would possibly compensate if that is the case? I'm going to disconnect this new one before I take off for Ohio just incase.. Don't want to fry another one if that indeed is the case.
You just need to get the right two gears in the 400Turbo to make the speedometer read correctly. The above photo actually shows a 700R4 ... but the 400 Turbo works the same way. If you know you rear end gear ratio and the height of your rear tires. It is just simple math to fix. Here is a on-line calulator ... that does all the math for you http://www.tciauto.com/Products/TechInfo/speedo_gears.asp Just plug in your numbers and it will tell which gears you need. Here is a on-line chart with the gears ... http://www.tciauto.com/Products/TechInfo/speedo_gears.asp#400
There used to be a speedo box that held gears that you could change to correct speed being off,it went on the speedo drive and had 3 gears in a box with an output to hook up the cable .Ck speedo shops.
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