I have a 94 TA with a stock rear. I have an opportunity to buy a complete borg warner posi rear, axles and all with a a 3.54 gear ratio.
What I need to know, is what my current gear ratio is. I have an automatic. I do have what I think is calle the build sheet. The only thing on it that is related to the rear is as follows:
"Axle Rear 9PM"
Does this mean anything, if not, how do I determine the gear ratio.
Thanks

I just checked the build sheet again and see that I have a GU5 code which is 3.23 gears.
Do you think it is worth changing the entire rear with the borg warner which has the 3.54 and is suppose to be much stronger ?

 

Either a 3.23 or a 2.73. Does your shifter have a marking for 1 or does it just go down to 2?? If only 2, then I believe it's a 2.73. If it's showing 1, I think it's a 3.23. Or vice versa.

 

Jack up the rear, unless you can see the D/S, have a friend help. Turn the wheel one full turn and count the number of times the D/S turns. The number of turns will be the gear ratio, i.e. almost 3 = 2.73, little over 3 = 3.23 and so on.

 

Now that's going out of the way!

If you can shift to 1st = 3.23s

If you can only shift to 2nd = 2.73s

 

An even simpler way to find out is: next time you go out riding, pop it into 3rd (1:1 ratio) and drive at exactly 70 mph. Your rpms will coincide with you rear gear ratio. I.E.- about 2700rpm indicates 2.73s, ~3200rpm indicated 3.23s, and so on.

I've done this with both the A4 and the M6. The A4 test was spot on at 2700rpm with the 2.73s. Now with the M6 in 4th (1:1) it turns right at 3700rpm with 3.73s. Piece of cake

 

That's a pretty cool idea, I think I'll give it a try, thanks.

 

You can also look at the RPO code in the glove box.

Assuming the gears haven't been changed, here's the codes:

GU2 = 2.73 gears
GU4 = 3.08 gears
GU5 = 3.23 gears
GU6 = 3.42 gears


If the gears have been changed, you'll have to either try one of the methods above, or pop the cover and get the tooth counts off the ring gear. Then divide the ring number by the pinion number and that gives you the ratio.