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Checking an axle ratio

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vping

vping

Yoda
Bronze
Country flag
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How is it done? I have an extra TD rear that I want to check to see if it is a 5.125:1, 4.875:1 or a 4.55:1.

Once I do determine the ratio, how much do these bring the RPM's down in relation to the other? are we taking a 10 MPH different at 50 or a 2 MPH difference? I ask because I've heard that top speed is only about 50 in these.
 
David_DuBois

David_DuBois

Jedi Warrior
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Vince - If it is out of the car, the easiest way would be to open it up and count the teeth on the pinion and on the crown wheel. The counts are as follows: 5.125 - 8/41, 4.875 - 8/39, 4.555 - 9/41. The speed per 1000 RPM in top gear are: 5.125 - 14.42 MPH, 4.875 - 15.2 MPH, 4.555 - 16.3 MPH. These speeds are with the original tires fitted, bias ply 5.5X15.
Cheers,
 
Steve_S

Steve_S

Yoda
Offline
If on the car, jack up the rear end. Brake one wheel, then spin the other wheel exactly one turn while counting how many revolutions the drive shaft makes. Divide that number in half and you have your ratio. You can spin the wheel half a turn instead but a full turn then dividing by two seems to narrow the margin of error.
 
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