Thread: Gear ratio

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I just bought a 1955 210, I have been trying to get the speedometer to work right. I replaced the cable to get it to stop jumping around and now it is about 10-20 MPH off. I am guessing the rear axel is not orginal and I am trying to figure out what the ratio is. Is there a trick to figuring out the gear ratio with out taking the rear end apart? I have already looked all over the axel for some sort of tag or mark saying what the ratio is. Thanks!

Jack up the back of the car and put it on stands. Mark the pinion and rear end with a line and then spin the right rear wheel one revolution while counting the number of times the pinion goes around. The trans will have to be in neutral. If the pinion goes around 3 1/2 times you have a 3:43 - 3:55 approximately. A little over 3 1/2 and it could be a 3:73. Under 3 times and it would be a 2:73 or so. This will get you in the ball park but is not as accurate as pulling the cover.
Mark

Astroracer--that works with a posi, but an open rear you jack up one wheel and turn it twice while counting pinion turns. Its plenty close enough if you know the possible ratios for your rear, you can tell the difference between , say, a 3.23 and a 3.08.