Hi All,
I am learning all the time, and am very grateful for this forum. I have an untagged rear axle, & am wondering what the gear ratio is, it must be a "middle of the road gear" since my engine isn't screaming @ 60 mph on the freeway (no tachometer, sorry). It's a shortened 9" ford axle - Many Thanks Kenny for your posting of the sticky on rear axles. I started by putting the truck up on stands, I rotated the tire (passenger side) 1 rotation & counted 1-3/4 rotations of the drive shaft. Thinking it too low, I rotated the tire 1 more turn & got 3-1/2 turns of the drive shaft (1:75 ratio again). I did a 3rd rotation & got 5-1/4 turns (1:75 again, very consistent). 1.75 sounds way too low & is also 1/2 of 3:50, which seems too coincidental. Any ideas what I am doing wrong, or how I am mis-interpreting the results?
Thank You & Regards,
Jon

 

Both tires must turn at the same time wile you are turning. If you are only turning 1 tire only and got 1.75 with a open diff. Then I you can take 1.75x2=3.50 like you thought. I would try and do it with both wheels and see for sure.

 

Actually, both wheels WILL turn at the same time only if you have a posi or limited slip type rear end, but if you don't have a posi, when you turn one wheel the other one will either turn in the opposite direction, move partially, or stand still. Jack the truck up so that both wheels are barely off the ground and then block the wheel on one side from turning. Then you should be able to check the revolutions and determine the ratio accurately.

Vern

 

If the oposite wheel was not turning while you were doing this you have 3.50 gears.

The way you tell the ratio on open diffs is to jack up one side and rotate the tire 2 complete revolutions and count the yoke revs.