Eaton 913A315 Detroit Truetrac LSD for 8.875-in 30-Spline GM 12-Bolt Rear 3.73+

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Product Specification:

SKU:EAT913A315

MPN: 913A315

Weight: 25.9 lb

Inventory: 6

Type: Differentials

Vehicle Fitment

1964-1982 General Motors Half-Ton / Three-Quarter-Ton Trucks with GM 12-Bolt rear, 8.875" ring-gear, 30-spline axle shafts

Fitment Notes

Requires GM 12-Bolt "Truck" rear housing, 8.875" ring gear diameter, 30-spline axle shafts; will not fit GM 12-Bolt car rear without verifying housing specs.
Gear ratio MUST be **3.73 or numerically higher** (steeper) to ensure proper internal gear-clearance and performance.
Axle shaft diameter ~1.30 in; verify your shafts are compatible.
Only compatible with GM rear ends using 12 cover bolts ("12-bolt cover"); verify correct bolt pattern.

Features

Helical-gear limited-slip differential delivering torque bias smoothly in both forward and reverse.
Sealed, maintenance-free design - no wearable clutches, no external adjustments.
Quiet operation thanks to helical gears rather than clutch pack or plate-type LSD.
Designed to handle street, restoration, light off-road and towing use.
Durable construction from Eaton, proven in GM 12-bolt truck housings.
Supports ring gear ratios of 3.73 and steeper, allowing you to keep existing gears or upgrade.
Relatively light for its class (unit weight ~24 lb) to help reduce unsprung/rear end weight.
Proper bearing compatibility notes provided for small vs large bearing bores where applicable.

Specifications

Differential type: Helical-gear Limited Slip Differential (LSD).
Ring gear size: **8.875 in** (GM 12-Bolt truck rear)
Axle shaft spline count: **30 splines**
Axle shaft diameter: **~ 1.30 in**
Compatible gear ratios: **3.73 and up** (numerically larger)
Cover bolt pattern: **12 bolts** matching GM 12-bolt rear housing.
Product weight: **~ 24 lb**
Location: Rear axle application only.

Included Components

1x Eaton Detroit Truetrac differential carrier assembly (part # 913A315)

Product Description

The **Eaton 913A315 Detroit Truetrac** is a premium helical limited-slip differential engineered for GM 12-Bolt truck rears with 8.875" ring gear and 30-spline axle shafts. Designed to operate flawlessly with gear ratios starting at **3.73 and steeper**, this LSD gives you more traction without the drawbacks of clutch-type units - smooth engagement, minimal noise, and less maintenance. Ideal for Chevy and GMC half-ton and three-quarter-ton trucks from the mid-1960s through early-1980s that use the GM 12-Bolt housing.

This Truetrac replaces open differentials or worn factory LSDs, bolting in directly when your housing, ring-gear, spline count, and ratio are correct. Note: ensure your ring & pinion gears are within the 3.73+ range and that your axle shafts are 30-spline and ~1.30" in diameter. Bearing bore and cover bolt count must match the GM 12-Bolt truck spec. Fitment confirmed through 2024. 2025 unconfirmed.