10.5 - Rear Axle¶
Type: Sterling 10.5, full float
Source: 2005-2010 Ford F-350 Super Duty, SRW
Locker: ARB RD140 Air Locker
Axle Shafts: Factory 35 spline
Specifications¶
| Specification | Value |
|---|---|
| Type | Sterling 10.5, full float |
| Source | 2005-2010 Ford F-350 Super Duty (SRW)2 |
| Width (WMS) | 68.87"2 |
| Bolt Pattern | 8x1702 |
| Spline Count | 35 (shafts), 31 (pinion)2 |
| Locker | ARB RD1403 |
Housing Identification
Corporate Sterling is identified by the absence of a filler hole in the OE inspection cover. Housing must be 2010 or earlier; 2011+ went to a different pinion spline and 5.13 gears do not exist for it. A 2008-2010 housing also needs an extra pinion spacer with the gear install kit (see Ring & Pinion).
Ring & Pinion¶
| Specification | Value |
|---|---|
| Ratio | 5.13 |
| Manufacturer | Revolution Gear |
| Part | F10.25-513L (long spline)4 — sourcing TBD #297 |
| Install Kit | Revolution 35-20465 |
| 2008-2010 Housing | Add Revolution SK F10.5-Conv pinion spacer (sold separately)5 |
Gear and Housing Mismatch
There is no 10.5-native 5.13. This is a 10.25" ring gear run in the 10.5 housing. Revolution supports the combination: the F10.25 long-pinion set fits both housings, and 35-2046 is the kit for a 10.5 housing running it (not 35-2046A, which is for a factory 10.5 gear).4 Add approximately 0.120" to the pinion depth stack as a starting point, then adjust. A solid crush sleeve spacer works without modification despite not being listed for the 10.5.2 RD140 fitment with this gear: TBD #300.
Differential¶
| Specification | Value |
|---|---|
| Locker | ARB RD140 Air Locker3 |
| Spline | 35 |
| Ratio Coverage | All ratios (no carrier break)3 |
| Solenoid Draw | ~2A |
| Control | SwitchPros Button 10, OUTPUT-10 |
| Air Source | ARB Twin Compressor via manifold |
Air locker selected over the Ford factory electric locker (BC3Z-4026-B). The air system already exists for the front locker, so the marginal cost is one solenoid and a 6 ft line. The e-locker has no published current draw, requires a housing pass-through and bulkhead connector, and its 12V-engage / 5V-hold profile is not reproducible on a SwitchPros output.6
See Air Lockers for wiring, air line routing, and operation.
Axle Shafts¶
| Specification | Value |
|---|---|
| Manufacturer | Factory |
| Type | Full float |
| Spline Count | 35 |
Brakes¶
| Specification | Value |
|---|---|
| Type | Factory Super Duty disc |
| Pads and Rotors | PowerStop Z36 Truck & Tow |
| Park Brake | 8.1" drum-in-hat, mechanical2 |
Factory disc with integrated park brake. No conversion required. Master cylinder sizing, flex hoses, proportioning, and bias are on the Brakes page.
Housing Preparation¶
| Item | Part |
|---|---|
| Truss | Motobilt |
| Differential Cover | Motobilt |
| Pinion Yoke | 1350, 31 spline, strap style |
| Brackets | TJ/LJ suspension brackets |
| Breather | Relocated; braided line routed high into the engine bay |
Pumpkin is offset to the passenger side with a longer driver-side tube. Lay out ORI lower mounts and link brackets before the truss goes on. Pinion pointed at the transfer case for the CV driveshaft (see Driveshafts).
All welding completed before internals installed.
ABS and Tone Ring
No ABS on this build; speed is GPS-sourced via the Dakota Digital GPS-50-2. Tone ring omitted and the sensor opening plugged; an unplugged housing opening leaks gear oil. The arrangement depends on the donor year, the same 2008 boundary as the gear install kit.1 Plug sizes: TBD #310.
Outstanding Items¶
🔴 Critical (1)
- Rear 5.13 long-spline gearset (Revolution F10.25-513L) sourcing confirmation (#297) — There is no 10.5-native 5.13; the rear Sterling 10.5 runs the Revolution F10.25-513L (Ford 10.25" long pinion) with master kit 35-2046. Confirm availability and lead time with Revolution or a dealer before ordering the kit. A 2008-2010 donor housing also needs the SK F10.5-Conv pinion spacer (sold separately).
High (8)
- Re-spec 8HP70 → NP241OR adapter path (case changed from JK NV241 to TJ Rubicon Rock-Trac) (#313) — The transfer case selection changed from the JK NV241 GenII Command-Trac (2.72:1) to the TJ/LJ Rubicon NP241OR Rock-Trac (4:1) (owner decision, 2026-09-18 — deeper low range). All the adapter research on the transfer-case page was done against the JK case and does not carry over automatically.
- iBooster pedal ratio verification against 1.25" booster stroke (#301) — Verify the brake pedal ratio (approximately 4:1 per owner notes, 03-06 TJ/LJ auto pedal) against the Bosch Gen 2 iBooster's 1.25" stroke so the pedal reaches full booster travel without the cylinder bottoming, with the 1-1/8" Wilwood master and Super Duty calipers at all four corners. Bench-measure on assembly.
- ARB RD140 fitment with Revolution F10.25-513L in the Sterling 10.5 housing (#300) — The rear runs a 10.25" ring gear (Revolution F10.25-513L) in the 10.5 housing with the ARB RD140 carrier (Ford 10.25/10.5, 35 spline, all ratios). Confirm with ARB or Revolution that the RD140 flange and ring gear bolt pattern match the F10.25 gear in this housing before ordering, and confirm the pinion depth starting point (owner note: add roughly 0.120" to the pinion depth stack).
- Ball joint delete clearance against ORA high steer arms (#299) — Verify the American Iron ball joint delete (upper and lower, welded) clears the Offroad Anonymous 05-16 Super Duty Dana 60 weld-on full hydro high steer arms through full steering travel (40 degree target with the 8" PSC ram) and full suspension travel.
- Front axle ball joint delete bushing offset (0 / 1.5 / 3 degree) (#298) — American Iron ball joint delete bushing offset sets caster and camber together, summing to the bushing rating. Select after caster is measured with the Dana 60 under the vehicle at ride height. Every 15 degrees of bushing rotation gives 0.5 degrees of change on a 3-degree set.
- 4WD/4LO indicator — NP241OR position switch → PMU → HDX (measure switch at teardown) (#145) — Reversed 2026-09-18 — the 4WD indicator is wanted after all. (Previously closed as "omit the indicator.") Updated the same day for the transfer-case change from JK NV241 to TJ/LJ Rubicon NP241OR (#313), which makes this easier.
- Turbolamik Aux: P/N (#48) — Confirm aux output channel + pinout configured for P/N (start interlock)
- Turbolamik Aux: Reverse (#47) — Confirm aux output channel + pinout configured for Reverse signal -> PMU In 3
📋 Medium (9)
- ABS sensor opening plugs, front and rear axles (#310) — With no ABS on the build, the tone rings are omitted and the wheel speed sensor openings must be plugged. An unplugged opening in the rear housing is a gear oil leak path.
- Confirm ORA high steer kit quantity (per arm vs per pair) (#302) — Confirm whether the Offroad Anonymous 05-16 Super Duty Dana 60 weld-on full hydro high steer kit is sold per arm or per pair before ordering, so the purchase tracker quantity is right.
- Steering Cooler Fan (electrical) (#101) — On PMU Out 8 (~15A, 180F inline thermostat); confirm actual Mishimoto fan draw fits budget
- Steering Pump Specs (#99) — Kit pump PK40JP2-FH is Jeep 4.0L-only - source Cummins R2.8 PSC pump/bracket; flow/pressure/drive TBD
- Rear Suspension Components (#98) — Coil rate, bypass valving, control arms, track bar, sway bar
- Front Suspension Components (#97) — Coil rate, bypass valving, control arms, track bar, sway bar
- Rear Driveshaft Specs (#94) — Custom (Tom Woods) decided - measure length at final ride height & order
- Front Driveshaft Specs (#93) — Custom (Tom Woods) decided - measure length at final ride height & order
- Transmission Pilot Bearing (#91) — If required by flywheel/crank combination
📝 Low (2)
- Steering Reservoir & Fluid (#103) — Fluid = PSC/SWEPCO 715; remote reservoir (in pump kit) model/location + system fill qty TBD
- Suspension Geometry (#102) — Departure and breakover angles (calculated from chosen suspension)
Build Tasks¶
- Verify no filler hole in OE inspection cover
- Confirm donor housing year; a 2008-2010 housing needs the Revolution SK F10.5-Conv spacer in addition to kit 35-2046
- Confirm park brake hardware complete
- Cite an OEM or vendor source for WMS width, 8x170 bolt pattern, and spline counts before bracket layout or wheel order
- Locate and plumb the axle breather before the truss is welded
- Confirm the Motobilt cover fill plug clears the truss, and whether it includes a drain plug
- Adjust and verify park brake shoes before the axle goes under the vehicle
Related Documentation¶
- Front Axle
- Air Lockers - Locker control, air lines, operation
- Air Compressor - ARB Twin Compressor and tank
- Driveshafts - Rear shaft yoke and CV
- Brakes - Master cylinder sizing, flex hoses, proportioning valve, park brake
- Suspension - ORI strut and link bracket layout
- Purchase Tracker - Axle swap parts
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Sterling 10.25/10.5 rear ABS: through 2007 the tone ring mounts to the differential carrier against the ring gear and the sensor reads it through a window in the axle housing; 2008 and later moved to a sensor at each hub with smaller rings. Vendor and service references via Torque King and DieselHub, accessed 2026-09-17. Confirm against the donor housing. ↩
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Owner build notes, 2026-09-16 — donor range, housing identification, WMS width, bolt pattern, spline counts, park brake size, pinion depth offset, and the solid spacer note. Not yet backed by an OEM or vendor citation; see Build Tasks. ↩↩↩↩↩↩
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ARB RD140 — Air Locker, "Ford 10.25/10.5 Inch", 35 spline, all gear ratios; $1,399.95. Revolution Gear listing, accessed 2026-09-16. Supersedes the RD116 (30-spline Dana 44) previously specified for the rear. ↩↩↩
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Revolution Gear F10.25-513L — Ford 10.25" long-pinion 5.13 ring & pinion. Revolution: "Ford 10.25 Inch (Long Pinion) Gear sets can be used in 10.25 Inch and 10.5 Inch Ford Differentials. Master Overhaul Kit P/N 35-2046 is required to use gears in a 10.5 Inch Differential." Revolution Gear dealer listings, accessed 2026-09-16. ↩↩
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Revolution 35-2046 — "Fits 1993-99 Ford 10.25 Inch and 1999-2007 10.5 Inch housing with Revolution Gear F10.25 ring and pinion. 2008-10 10.5 Inch housings require spacer for install, sold separately, part number SK F10.5-Conv." revolutiongear.com, accessed 2026-09-16. Do not order 35-2046A, which is the kit for a factory 10.5" gear. ↩↩
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Owner decision, 2026-09-16 — ARB RD140 over the Ford factory e-locker (BC3Z-4026-B): the air infrastructure already exists for the front locker, and the e-locker's 12V-engage / 5V-hold drive is not reproducible on a SwitchPros output. ↩