Yukon Gear High Performance Gear Set For 10 & Down Ford 10.5in in a 4.88 Ratio
When a 1999-2010 Super Duty or Excursion goes from stock tires to 37s, or a diesel truck spends its life pulling a heavy fifth wheel up grades, the factory 3.73 or 4.10 gears leave it straining. The Yukon YG F10.5-488-31 is a 4.88 ring and pinion for the Ford 10.5 in. full-floating rear of those years, and it is about as deep as most owners go in this axle.
The 1999-2010 Ford 10.5 uses a 10.50 in. ring gear fastened with 12 bolts and a 31-spline pinion. With 4.88 gears the driveshaft turns 4.88 times for every turn of the rear wheels. Compared with a 3.73 that is about 31 percent more torque at the tire, and about 19 percent more than a 4.10, which is roughly what it takes to restore the original feel after a big jump in tire diameter. In a full-floating axle the shafts carry no weight, so the gear set and pinion bearings absorb all of the towing and tire load, which is why setup and break-in matter so much here.
Make sure the axle is the 10.5 and not the earlier 10.25, and read your current ratio from the door sticker axle code or the tag on the cover; our axle code and ratio guide covers both. If noise is the reason you are shopping, use the whine on acceleration vs deceleration guide to tell gear wear from bearing failure, and see the Ford 10.5 problems and rebuild cost guide for the usual failure points.
Fits 1999-2010 Ford 10.5 in. rear axles with the 31-spline pinion, the full-floater under F-250 and F-350 Super Duty pickups, Excursions and E-Series vans of those years. It does not fit 2011 and newer 10.5 axles, which went to a 37-spline pinion, and it does not fit the older 10.25. On a 4x4 the front axle has to be regeared to the same 4.88 ratio. Ratio-to-carrier and housing details vary by year, so send us your year and VIN if you want us to confirm before ordering. If 4.88 is more than you need, compare the 4.11 set and the 3.73 set for the same axle. Other heavy axle gears are in the hard parts collection.
Yukon's setup chart for the Ford 10.25 and 10.5 lists about 0.025 in. OEM pinion shim depth, 20-35 in-lb of pinion bearing preload with new bearings, 95 ft-lb on the ring gear bolts and 80 ft-lb on the bearing caps. Set pinion depth first, then preload, then backlash, and read the contact pattern with marking compound before closing the cover. Replace the bearings, races, pinion seal and crush sleeve together; the Revolution 10.25/10.5 master install kit or the Yukon master overhaul kit for 2007-and-older 10.5 covers them. Use 75W-90 or 75W-140 gear oil with friction modifier for a clutch-type limited slip. Yukon recommends a short first drive of 15-20 miles with a cool-down, no towing for 500 miles and an oil change after that. Yukon also lists 37 in. as its maximum recommended tire for the Ford 10.25 and 10.5, so trucks going bigger should consider stronger axle parts.
| Brand | Yukon Gear & Axle |
| Part number | YG F10.5-488-31 |
| Fits | Yukon Gear High Performance Gear Set For 10 & Down Ford 10.5in in a 4.88 Ratio |
| Type | Final Drive Gears |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. 2011 and newer Ford 10.5 axles use a 37-spline pinion. This set is the 31-spline version for 1999-2010 axles.
On a 1999-2010 Super Duty, 4.88 is usually paired with 37 in. tires or with heavy towing on stock-height tires. Diesel trucks often run a little shallower than gas trucks on the same tire.
Yes, on a 4x4. The front axle must have the same 4.88 ratio or the drivetrain will bind in 4WD.
New pinion and carrier bearings and races, a pinion seal, crush sleeve and shims. A 10.25/10.5 master install kit or overhaul kit supplies them. You will also need gear oil and friction modifier if you have a limited slip.
Yes, any ratio or tire change affects it. Most of these trucks need the speedometer recalibrated with a programmer or tuner after the regear.
