Sterling 10.50
Fact: This axle received a larger ring gear, which improved its overall strength and addressed the premature failure issues of the 10.25-inch axles when used with 4.10:1 or numerically higher gear ratios. Unfortunately, it was designed with a smaller pinion bearing than its predecessor.
Found under: '99-'05 F-250 and F-350
Type: Full-float
Weight (lb., approx): 333 (single wheel), 348 (dual wheel)
Ring gear diameter (in.): 10.50
Pinion shaft length (in.): 10.50
Pinion shaft spline count: 31
Axleshaft spline count: 35
Axleshaft diameter (in.): 1.5 (at the splines)
Hypoid offset (in.): 1.50
Gear ratio range: 3.08-7.17
Brakes: Disc
Normal GAW range (lb.): 9,750 (single/dual wheel)
Nominal GCW rating (lb.): 26,000 (single/dual wheel)
Output torque maximum (lb-ft): 10,660 (single/dual wheel)
Output torque continuous (lb-ft): 2,900
Weak points: This axle uses an inner bearing and race that is not as large and strong as the bearing and race used in the 10.25-inch axle. Also, the ring gear is mounted to the carrier using bolts that are non-shouldered and tend to loosen, resulting in the possibility of catastrophic damage to the differential. This is actually a problem that affects both the 10.25- and 10.50-inch Sterling axles.
Fixes: To address the bearing and race issue, you can use the ring-and-pinion from the 2nd-generation 10.25-inch. The trade-off is that you'll get a slightly weaker ring-and-pinion, but you'll get a larger inner bearing and race. To solve the ring-gear bolt problem, replace all of the bolts with shouldered bolts. The technicians at Custom Differentials can set you up with shouldered Dana 70 ring-gear bolts.
Hot tips: If you're short on cash during a rebuild (depending on the ratio you want to use, factory parts for the 10.50-inch Sterling can be almost double the cost of 10.25-inch aftermarket parts), you can use the 2nd-generation 10.25-inch case/carrier and gearset in the 10.50-inch housing (as mentioned above). This can significantly lower your parts bill. Also, a three-spider case/carrier is available instead of a normal two-spider gear case/carrier. This update increases the strength and longevity of the differential because the third-spider gear helps share the load when delivering power to the tires and helps reduce spider-gear wear and failure.
This is a 2nd-generation 10.25-inch Sterling axle. From the outside it looks no different than either the 1st generation 10.25-inch or the 10.50-inch axle. All of the Sterlings found under the '85-and-up F-250 and F-350 pickups boast durable axleshafts with unique O-ring seals. Unfortunately, these axles also sport non-shouldered ring-gear bolts that can loosen and cause major damage. | 
When it comes to beefing the 10.50-inch Sterling, a very effective method is to replace the two-spider gear (left) with a three-spider gear. We used a GM three-spider for this illustration. Upgrading to a three-spider gear/case will increase the strength and longevity of the differential because it helps share the load when delivering power to the wheels. This helps reduce spider-gear failure. | 
If you own a '99-and-up Super Duty, that's your pinion bearing on the right. If you want the larger bearing, you'll have to swap in the ring-and-pinion from a 2nd generation long-pinion 10.25-inch axle. This will give you a larger pinion bearing but a slightly weaker ring-and-pinion. |