how do you determine rear gear ratio?

I have a non-posi rear end

how do i determine rear diff gears without having any id tags.

Turn the wheel check the drive shaft. Need some help? Anyone have some instructions.

Thanks for the replies guys


Found a goodwebsite and here is the answer

Determining which kind of differential you have
1. The vast majority of cars have an open differential as it is cheaper to manufacture, has no clutches to wear out, and is generally better-behaved. But posi units are out there, sold under titles of "Traction-lok", "Sure Grip", "Limited Slip" and the like. The concept is to place a clutch pack in-between the left and right end-gears, trying to force both wheels to turn the same speed at all times. Of course, to turn a corner, the wheel speeds must vary - thus the clutch-pack friction between the two end gears cannot be set extremely high or you'll suffer from hard steering (the car will want to continue in a straight line) and accelerated tire wear. OK, I've said enough. You get the picture.


2. Secure the car from rolling forwards or backwards and place the car in Park (if you have an automatic) or first gear (if you have a manual trans). Raise the rear end of the car so both rear tires are off the ground. Place jackstands under the car to safely support it.


3. Try to rotate the left wheel. You have "locked" the driveshaft from turning by placing the car in Park (or in gear), thus posi or no posi, the other wheel MUST turn the opposite direction at the same speed. If you have an open differential, this will take minimal effort. The wheels will rotate in opposite directions at the same speed. If you have a limited-slip differential though, the clutches don't like to let this happen so they'll fight you. A lot. A tight posi might take over 100 lb-ft to get the wheel to turn. By this point you'll know which procedure below you should use.

4. Open differentials: Secure the car from rolling forwards or backwards and place the car in neutral. Raise ONE SIDE of the car off the ground (left in this example) and place jackstands under the car to safely support it. If you just did steps 1-3 as a test, note that this is different from step 2, requiring you to change your setup.

5. Place a mark on the tire at bottom-dead-center. Crawl under the car and place a mark on the driveshaft. You'll be counting how many times the driveshaft turns in this test, so place the mark at a convenient place that you can call "zero".

6. Have a friend turn the left wheel for 20 rotations. Have them count to themselves while you count driveshaft rotations. When they are completed, divide the number of driveshaft revolutions by 10. For instance, 30 turns is a 3.00 differential ratio. 37 and a third turns is a 3.73 ratio. If you know the factory-available ratios, this will put you close enough to quickly determine which ratio you have. If you don't know the factory options, then do a larger number of wheel rotations (say, 100) and divide by 50 for a little more accuracy on that last decimal place. You're done! You can put the car back on the ground now.