I have an LSD and the tag is missing. How would I figure out the gear ratio without opening it up? Is that the only option I have? Thanks

It is a 3.70 if it came from an older Subaru. If from a newer Legacy, who knows?

Spin the input shaft, and count the number of times the diff stubs spins per spin, or visa versa, and count the number of spins it takes to spin the input shaft.

 

Twitch

 

PS: I may have that backwards...

This should answer your question...

 

 

A little research before spitting out answers helps alot.

Thank you for the information. That's an easy to remember formula.

Tried the spinning and counting and got 1.9-2.0 count on the ratio. Turned the input yoke locking one output spline, tried counting the yoke by turning the output spline ,with one locked down. 1.9-2.0 to 1. never read about ratio's like that. What did I do wrong?

what is the car it came from?

I have an LSD and the tag is missing. How would I figure out the gear ratio without opening it up? Is that the only option I have? Thanks

 

Pulling the rear cover is the best way to be sure. You don't need to unbolt the side bearings though.

 

It will give you a good chance to inspect the gear teeth and the spiders, and change the fluid.

 

Just use good sealant for reassembly.

Tried the spinning and counting and got 1.9-2.0 count on the ratio. Turned the input yoke locking one output spline, tried counting the yoke by turning the output spline ,with one locked down. 1.9-2.0 to 1. never read about ratio's like that. What did I do wrong?

 

Hold on, if you were able to lock one diff stub in place, you either don't have

an LSD, or its completely shot.

 

And if you accidentally counted every 1/2 turn rather than every full turn, it

sounds like you have a 3.9.

 

Twitch