The table below you will assist you with determining just what rear end ratio you have by using your RPO code, answering the question: What rear end ratio was in my Chevy or GMC vehicle when it left the factory. You can typically locate your RPO code on driver side door panel or glove box.

General Motor rear end differentials are referred to by the diameter of the ring gear, i.e. 7.5, 8.5 inch, 10.5 inch.  Our experts can help you find the correct ring and pinion set.  Give us a call at 800-216-1632 to get started. We have a large selection of gear sets in stock and can recommend the correct gear ratio to match you engine horsepower, transmission specifications and tires to give you the desired performance.

Switching your rear end gear ratio helps your gas mileage or improves your power!

If you need more gas mileage, you want to switch to a higher gear ratio.  If your looking for more power or performance, you would switch to a lower ratio.  It's just backwards from the way we think, if you have a 4.10 ratio and need more fuel mileage you would switch to say 3.42 or 3.73.  If you have a 3.42 rear end ratio and need more towing power you would switch to say 4.10.  If you have installed larger tire they rob the performance and you would want to go to a lower ratio say 4.56 or 4.88 depending upon your tire diameter.

Want to search for rear end parts by application, ask the Gear Wizzard

We specialize in matching your tires and ring and pinion ratio for your specific application and needs.   Thinking about changing tire size we can help, consult our Look up chart for determination of engine RPM, gear ratio and tire size combination.  Larger tires on lifted truck suffer from loss of power, changing the ring gear and pinion to a lower ratio is the answer.

Why you need a positraction?

Without positraction only one rear wheel receives the power.  In bad road conditions say, mud, ice or snow traction to one wheel is bound to get you stuck.  Installing a positraction provide power to both wheels at the same time, a significant improvement in traction.  For positraction replacements and parts see the following link.  Positraction units are available for many General Motor FWD Front Wheel Drive models.

A chart is also provided which presents Differential cover/cover gasket shapes, a common technique to identify differential ring gear diameter.  And a Dana/Spicer Parts illustration showing how to locate the Dana bill of material number is provided. This is a critical number to ensure that you find correct Dana parts the first time.  For example Dana used in some cases 3 to 4 different ring gear widths for say a Dana 35 ring gear, so the set up is not the same for each gear category. 

When ordering Dana/Spicer Differential Parts provide bill of material number. This number is stamped on your right hand side axle tube. It's a number like 603XX-X, 604XX-X or 605XX-X. With this number you can tell exactly what components the factory used in the assembly of your differential.