What's the quickest way to figure out if I have 3.73 or 4.10 gears on my 2001 Suburban 2500?

 

Put the transmisson in neutral and jack up one rear wheel (the other MUST stay on the ground). Make a mark on the driveshaft, or watch the U-joints, and make a mark on the tire in a location you can remember EXACTLY - at the very bottom may be best. Spin the wheel that's off the ground exactly two turns, counting the driveshaft revolutions. The number of shaft revolutions is your rear end ratio.

Since I gather you've narrowed it down to two choices, you really only need to know whether the shaft goes around more or less than 4 turns.

Regards,

David

 

You can find you factory ratios on your SPID label (Most likely in your glove box). Also zx1100fl has access to your original build sheet and can tell you. PM him, he is extremely helpful.