Eaton Detroit Truetrac Differential 31 Spline 1.32in Axle Shaft Dia Front 8.8in/Reverse Rear 8.8in
The Eaton Detroit Truetrac 913A561 is a helical-gear limited-slip carrier for the Ford 8.8 in. axle with 31-spline, 1.32 in. C-clip shafts. That is the axle under a long list of F-150s, Mustangs, Explorers, Expeditions, Rangers and Crown Victorias, and drivers usually go looking for this part when a worn Traction-Lok chatters in parking lots, or when an open carrier lights up one tire on a wet road or a gravel launch. It needs no clutches, no switch and no special additive, so it suits a daily driver that still needs to put power down.
The Truetrac replaces the usual cross shaft and spider gears with pairs of helical pinions running in pockets in the case, meshed with helical side gears. Driving straight or turning normally, the gears spin freely and the axle behaves like an open differential. When one tire starts to slip, the helical teeth thrust against the pocket walls and case, and that friction biases torque toward the tire with more grip. There are no clutch plates to wear, which is the main reason 8.8 owners move to it after rebuilding a Traction-Lok more than once.
Lift one rear tire with the transmission in neutral and turn it. If the opposite tire turns backward, the carrier is open or its clutches are gone. Before buying, count the axle splines or check the axle tag, since the 8.8 came with both 28 and 31 splines. Our 28 vs 31 spline guide shows how to tell. If you have a chattering Traction-Lok, try the steps in 8.8 Traction-Lok chatter fix first, and compare options in Detroit Locker vs Truetrac.
Eaton's application guide lists 913A561 for 1987-2011 Ford C-clip 8.8 in. axles with 1.32 in. 31-spline shafts, all ratios, in both passenger car and F-150, truck, SUV and van applications. The catalog name also references front and reverse-rotation 8.8 housings; those share the 8.8 ring gear size but not always the same carrier, so match it carefully. For the 2009-2023 F-150 4x4 front axle, Eaton catalogs a separate unit, the 917A738 F-150 front Truetrac. The 2015-up F-150 Super 8.8 uses 34-spline shafts and does not take this carrier. Send us your year and VIN or the axle tag if you want us to check. More axle parts are in our hard parts category.
| Brand | Eaton |
| Part number | 913A561 |
| Fits | Eaton Detroit Truetrac Differential 31 Spline 1.32in Axle Shaft Dia Front 8.8in/Reverse Rear 8.8in |
| Type | Differentials |
| 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. It is for 31-spline, 1.32 in. axle shafts. A 28-spline 8.8 needs a different carrier, so count your splines or check the axle tag first.
No. Eaton lists 913A561 for all ratios in the Ford 8.8, so there is no carrier break to worry about.
Not the rear. The 2015-up F-150 Super 8.8 uses 34-spline shafts. For the 2009-2023 F-150 4x4 front axle, Eaton catalogs Truetrac 917A738.
A GL-5 mineral-based gear oil is recommended. Synthetic is acceptable if the axle maker allows it. Do not add friction modifier.
A helical limited slip needs some load on both tires. If one is fully in the air, light brake pressure helps it bias torque. A locker drives both wheels regardless.
New carrier bearings and races, ring gear bolts and a cover gasket or sealant at minimum. Replace pinion bearings and the seal too if the axle has high miles or whines.
