I have been told you can check the rear end gear ratio by jacking rear up and rotating the rear wheels on rotation and counting the # of times the driveshaft also rotates?? Is this correct and accurate. This seems to a much easier way than pulling the rearend cover to get #'s off the gears. any thoughts suggestions. Before replacing my trans i want to be sure my trans is a posi 3:70 ratio in my 69 z/28.

if it's a posi- that method works. as long as both wheels turn the same direction when you either spin a wheel or the yoke, you just count how many times the yoke turns when you turn a tire one full revolution. if it's a one-legger, i think you leave one wheel on the ground and do it, then multiply how many times the yoke turns by 2.. i think..

If it is a posi and both wheels turn together then turn the wheels exactly one turn and count the number of times the drive shaft turns. If it isn't a posi then leave one wheel on the ground and turn the other wheel exactly 2 turns and count the number of times the drive shaft turns. If the drive shaft turns 3 3/4 times then it is a 3.73, if it turns 3 1/3 times then it is a 3.31, if it turns just over 3 times then it is a 3.08, if it turns 2 3/4 times then it is a 2.73...

i just did that on my car...it doesnt have posi and i got 2 1/2. Am i mistaken or do i really have some crazy freeway gears...

It'sprobably a 2.56. Did you turn one wheel exactly 2 full turns with the other wheel held still?

yep and i got 2 1/2. are those stock gears most likely?

Yes, those would be stock gears.

jacked up the rear of my 69 z/28 today!!! With both wheels off the ground when i turned the tire forward the opposite wheel also turned in same direction. Does this tell me i have a posi rearend???? Also when i turned the lft tire and counted the yoke turns i got a different count from if i turned the rt. wheel and counted the yoke turns??? When i turned the rt wheel i got 3 3/4 turns of the yoke. When i turned the lft wheel i only got 2 1/2 turns??? Any thoughts. Also i tried putting one tire on the ground and turning and got also the 3 3/4 yoke turns. Am i correct in that i have a 3:73 posi???

Todd Miller

My old 10 bolt open would turn both of the tires the same way when it was jacked up. You may have an open rear end. Got the numbers from your axle tube? (If it's got the original guts).

Todd,
You could have a standard differential with galded pinion gears and cross shaft. You may also have a posi. The only way to be sure is to remove the cover and look at it. The reason you got different numbers each time is because something in the differential was slipping when you were turning it. Try putting one wheel on the ground and turn the other one exactly 2 times. It may be a little difficult to turn, but you will get more accurate numbers.