With new gears on the carrier and the pinion assembly, everything was put back in the housing to start the adjustment part of the installation. Afterward, we set the backlash to zero, with those cool threaded carrier pre-load adjusters we mentioned earlier, meaning the carrier was adjusted over to engage the pinion. The tech broke out the dial indicator and set up the final backlash, which should be between 0.005 to 0.008 inch. | 
With the backlash set and locked down, it was time to check the gear engagement. By coating the ring gear with grease and then spinning the assembly by turning the yoke, you will get... | 
...a visible wear pattern on the ring gear. Again, this is where experience comes in to play. Knowing what an acceptable wear pattern is and how to get it is beyond most of us normal gearheads. |
Changing the thickness of the shims placed between the pinion assembly and the housing will adjust the engagement of the two gears and set the wear pattern. | 
Once the technician was happy with the wear pattern, everything was torqued to the proper specs, and then the diff was filled with new 90W fluid. A bottle of friction modifier was also dumped in to cut down on heat. | 
After the job was complete, the technician put the spare tire back in and took the truck out on its maiden voyage to break in the gears. Yes, the gears need to be broken in, which basically means light pedal for the first 20 miles. Pull over and let the gears cool off, and refrain from towing or hard launches for the first 500 miles. We know it might be hard to control the gas pedal with a lead foot, but try to show some restraint until the gears are properly broken in. |
The Final Word
This story's Final Word should be called the Final Math Problem. Check out the math equation we put together to justify the gear swap.
By this math, you can see that we have a projected savings of 2,600 bucks and some change, which is not bad for a few parts and a day's worth of work.
Stock Vs. Regeared Rearend
| STOCK GEAR RATIO | 4.10 |
| 70 MHP CRUISING | 2,800 rpm |
| FUEL ECONOMY | 10.97 mpg |
Money Saved Via Increased Fuel Economy
| STOCK REAREND |
10.97 x 33 gallons =
362.01 miles per tank of gas |
| REGEARED GEAR RATIO | 3.21 |
| 70 MPH CRUISING | 2,400 rpm |
| FUEL ECONOMY | 11.43 mpg |
| REGEARED REAREND |
11.43 x 33 gallons =
377.19 miles per tank of gas |
Now There Is An Extra 15.18 Miles Per Tank Of Gas!15.18 miles x 52 fill-ups (average) per year = 789.36 miles 789.36 miles x 3.33 gallon (average price for 91 octane fuel) = $2,628.56 saved