Eaton 917A739 Detroit Truetrac Limited Slip Differential for 2015-23 Ford F-150

Vehicle Fitment

• 2015-2023 Ford F-150 (XL, XLT, Lariat, King Ranch, Platinum, Limited, Tremor, Police Responder, SSV trims) Rear 8.8-in axle

Fitment Notes

• Requires 8.8-inch rear axle with **34-spline** axle shafts
• Fits gear ratios 3.31 & up (factory 3.31, 3.55, 3.73, etc.) but **does not** fit OEM Electronic Locking Differential (ELD) models - must be for open or non-locking rear ends. 
• For rear application; front differential or front 8.8 variants (if exist) require different part number (e.g. 917A738) 
• Fitment confirmed through model year 2023; 2024-2025 unconfirmed unless explicitly specified by vehicle build doc (Eaton's listing covers up to "Ford F-150 2015-2023") 

Features

• Helical-gear style limited-slip differential, delivering smooth power transfer and traction without harsh locking behavior 
• Works in both forward and reverse directions, automatically biasing torque when needed 
• Optimized for Ford's 8.8-inch rear axle with 34-spline shafts, 1.32-inch shaft diameter 
• Compatible with gear ratios of 3.31 and higher (factory or aftermarket) without interfering with fitment 
• No electronic locking mechanism needed - this is a passive limited-slip unit ideal for daily driving, street, towing, or mild off-road traction improvements 
• Maintenance-free design; requires standard gear oil (petroleum/mineral GL-5 80W-90); synthetic or friction modifier lubricants are not recommended 
• Ring gear size of 8.8-inch ("8.8 in") for seamless installation in stock 8.8 housings without modification 
• Product weight around 27 lb, robust build to handle torque loads typical of F-150 use 

Specifications

• Axle type: Ford 8.8-inch solid rear axle
• Spline count: 34 splines on axle shafts 
• Axle shaft diameter: ~1.32 inches 
• Ring gear ratio: 3.31 & up (factory 3.31, 3.55, 3.73 etc.) 
• Ring gear diameter: 8.8-inch nominal, to fit OEM 8.8 housing
• Differential type: Limited-Slip (Detroit Truetrac) 
• Product weight: ~27 lb 
• Fitment confirmed through 2023 model year; 2024-2025 unconfirmed per Eaton listings 

Included Components

• 1x Eaton Detroit Truetrac differential assembly (complete carrier internals installed)
• 1x Differential cover gasket or appropriate seal (depends on interchange with OEM hardware; confirm with vendor)
• Set of hardware where needed (bolts, shims; check your existing hardware if reuse is desired)
• Instructions / installation guide from Eaton for proper preload / break-in procedure

Product Description

The Eaton 917A739 Detroit Truetrac is a premium limited-slip differential designed for the Ford 8.8-inch solid rear axle, specifically high-spline (34-spline) axle shafts. It offers smooth, side-to-side torque transfer without the abrupt engagement or noise of locking differentials. The helical-gear design ensures quieter operation in both forward and reverse, making it ideal for daily drivers, off-road users, or towing setups looking to improve traction and stability on slippery or loose surfaces.

This differential fits 2015-2023 Ford F-150 trucks (most trims: XL, XLT, Lariat, King Ranch, Platinum, Limited, Tremor, etc.) that have the stock 8.8" rear end with 34-spline shafts and 3.31 or higher gear ratio. It is *not* compatible with models equipped from factory with an Electronic Locking Differential (ELD), and must replace an open or non-locking differential. Installation is relatively straightforward using OEM mounting points, but requires correct gear oil (GL-5 80W-90, mineral-based), proper torque on hardware, and following Eaton's guidance for break-in. Fitment beyond 2023 for F-150 or newer models to 2025 is not explicitly confirmed by Eaton's published materials.