My "ratio" of crazy-pills

[Coltonis]

Umm so maybe I'm taking crazy pills, but I just tried to check the ratio on my rear differential and got some "interesting" results. (Its an "open"/non-posi , if that matters.)

I tried using the lift, spin, and count method. However, the first time I was counting how many times the tire went around for 10 turns of the drive shaft. I came back in an looked at the wiki and found I was supposed to count the opposite. So i went back out and did it the way it said; I counted the number of drive shaft turns required to turn the wheel 10 times.

At any rate none of my math seems to be panning out. Thought I might throw it out there see if anyone could shed some light.

First time, by turning the driveshaft 10 times the tire spun just under 8 times, like 7.8-7.9.

I couldn't make heads or tails of what that meant and thats when I went back checked and found I was counting backwards.

Second time, I counted just over 12 (like 12.25) turns of the drive shaft for 10 turns of the tire.

Does that mean I have a 1.2(?):1 ratio? Is that even possible? Did i do something wrong?

[svnt442]

When you spin only one tire you are actually doubling the speed of the tire because of the differential action of the spider gears.

Sounds to me like you have a 2.56 gear.

[monzaz]

Ok well to make sure that all goes smooth...This is what you need to do.
- remove the tire and the drum. This way the open diff spider gears will only tire from the ring and pinion spinning. IF you have ANY DRAG from the drum or tire the whole thing geats messed up from the spider gears turning.
-Next mark the axle in the 12 oclock position with chaulk, marker pencil or anything you can reference quickly.
- now mark the drive shaft parrellel with the ground maek the mark on the yoke dust sheild and onto the diff cast housing as again a reference start and finish point.
- NOW finally spin the drive shaft only!!!! the axles should both spin in the same direction...

- THE axle should only go around ONE FULL COMPLETE REVOLUTION. count how many times the drive shaft goes past the marked reference point and add the extra as a decimal...
IE 3 and 3/4 turns will probably be 3.73 ratio 2 3/4 turns will be 2.73 ratio and so on 2 1/2 will be 2.56 ratio 3 full turns of the drive shaft and a little past will be 3.08.

Hoe this help everyone.

Posi you can usually leave the tire and drum on if the car is a runner because of the clutches and cones keep the spider gears locked when turning the wheels. BUT it is still figure the same exact way. Jim

J D Race.com

[Coltonis]

Okay, that makes sense. There was definately only one wheel spinning, didn't realize it mattered. I could feel that there was some drag somewhere and either a drum or the gear box makes this wonderful noise like someone is sharpening an axe with a grindstone.

Looks like I get to learn how to rebuild the rearend too!

Thanks for the info.

[joe_padavano]

Originally Posted by monzaz

- THE axle should only go around ONE FULL COMPLETE REVOLUTION. count how many times the drive shaft goes past the marked reference point and add the extra as a decimal...
IE 3 and 3/4 turns will probably be 3.73 ratio 2 3/4 turns will be 2.73 ratio and so on 2 1/2 will be 2.56 ratio 3 full turns of the drive shaft and a little past will be 3.08.

All good info, but I like to turn the driveshaft to get TEN full turns of the wheel. The reason for this is that it is easy to tell the difference between 32.3, 33.1, and 34.2 turns of the driveshaft. Without a degree wheel and pointer, it is very difficult to tell the difference between 3.23, 3.31, and 3.42 turns of the driveshaft.