"You can check rear gearing by jacking up one wheel, and turn said wheel, while counting how many times the driveshaft goes around. One complete rotation of the wheel should turn the driveshaft 4.56 revolutions."

Close but no cigar, IMO. :-)

Given the way an open differential works, with one wheel stationary and 4.56 rear gears, you won't see 4.56 turns of the driveshaft to 1 turn of the wheel; you will see 2.28 turns of the driveshaft to 1 turn of the wheel.

Here's a post on the subject that should eliminate the guesswork:

Differential ratio?


BTW, I do agree that the tachometer or speedometer (or both) are grossly inaccurate if the car has stock diameter (~25.4") tires and the original 4.56 rear end. It calculates to around 3500 at 70 mph, which pretty much agrees with the R&T test from back in the day.

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Gary L - 142E ITB race car, 73 1800ES, 02 S60 T5