Alaska 86’ differential questions

[BJedi76]

86’ Sierra Classic 1500 4x4 swb

Is there a way to identify the differential gear ratio, without pulling the cover and physically counting them?

The front differential has not been replaced, but the rear axle was replaced (not by me).

My front driveline is missing and I want to make sure the differentials are the same gear ratio before I put in a front driveline.

Thank you...

 

[TubeTruck]

In the driveline section

https://www.gmsquarebody.com/threads/how-to-calculate-gear-ratio-wo-removing-covers.3860/

 

[FlockofGorillas]

1. Jack one wheel off the ground, put the transmission in neutral and take the parking break off. ***Be sure to use jack stands under the axle for safety precaution***
2. Mark the wheel and the drive shaft with chalk or masking tape.
3. Turn the wheel TWO revolutions and count the number of driveshaft turns.
4. The number of driveshaft rotations will help you determine your rear axle ratio. For example, if it turned 3 and a half times, it's a 3.50:1 ratio. If it turned 4 and a quarter times, it's a 4.25:1 ratio.
5. For better accuracy, turn the wheel 20 times and divide by 2 for your rear axle ratio.

this only works if its an open rear end.

 

[MikeB]

Many of the GM axles had a code stamped into the front side of the passenger side axle tube.

This for 70s cars, but it's an example. https://www.novaresource.org/axle.htm