Rear axel ratio

Posted by Jack Richard on March 04, 1998 at 10:32:20

In Reply to: MPH
posted by Jerome Bokelmann on March 03, 1998 at 08:31:42

Jerome-
You can tell what the rear axel ratio in your car is by jacking one rear wheel off the ground (block other wheels and release the parking brake). Put trans in high gear and remove your spark plugs. have a helper watch the rear wheel while you turn the engine over with the crank and count exactly the number of turns of the crank necessary to turn the rear wheel over twenty times.Divide the number of crank turns (and fraction of a turn) by 10 and that is the rear end ratio.If its still not clear, a more accurate result can be obtained by turning the crank until the wheel revolves 200 times, then divide the number of crank turns by 100, buts that's a lot of exercise!.

: I purchased my restored '29 coupe late last year so I am rather novice at this hobby.The max speed that I get out of it is around 45 mph (53 going downhill with a tail wind once).I just assumed that this is normal since times were slower and even Mike signs off with "God speed under 40".I just noticed in the "Model A Shop Manual" a chart that has RPM/Speed and my car more aligns with the AA truck. Now I'm not interested in driving more than 40mph (65 mph would scare me to death), I'm concerned that the RPM's for me to drive 40mph is higher than the average "A" driver out there. Thus premature engine wear.

: I assume (oh... how I hate to do that) that this is in the rear end and not the engine.Is this possible that I have a different gear ratio than most cars?What should the ratio be?How difficult is it to modify the ratio to get the car more normal.




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