Project FD RX7 Restomod: Part 15 – Building the Ford 8.8 Differential with a Detroit Truetrac LSD and WPC

We take a junkyard Ford Explorer 8.8” differential and transform it by installing a Detroit Truetrac limited slip differential, hand deburr the ring and pinion gears, WPC treat the gears and bearings, and modify the aluminum housing to fit the high-power goals, handling and drivability requirements of our FD RX-7.

The Ford 8.8” axle has been around since the 1980’s and has been used on everything from Mustangs to F-150s, Explorers and Crown Victorias.  The legendary performance of the 8.8 and the sheer number of cars that use this axle has created a massive aftermarket which has greatly driven down costs.  Gear sets can be found in almost any ratio with prices starting at less than $200, and there’s a wide assortment of limited slip differential options, rebuild kits, and upgrade kits on the market.

The solid axle Ford 8.8 has been the swap of choice for many domestic cars and trucks, and the Independent Rear Suspension (IRS) Ford 8.8” Differential is a staple in high horsepower road race, drag, and drift builds from import Supras and S2000s, to BMWs and domestic cars.

As soon as we realized IN PART 14 that upgrading to a Ford Explorer 8.8” differential was going to be a similar price as bracing the stock diff housing and installing a chattering aftermarket clutch-type differential, we immediately knew we were going to use the Detroit Truetrac Limited Slip Differential.

The Detroit Truetrac LSD (by Eaton) has always been one of our all-time favorite limited slip differentials.  The handling, performance, character, and smooth operation makes it perfect for street use, and performs incredibly well on the track.  The way the Truetrac handles high torque and puts down power in a consistent, predictable, and easy to control manner makes this helical (gear-driven) LSD one of the best modifications you can do to an S197 or S550 Mustang.

Unfortunately, this LSD is available mostly in domestic applications from Ford, GM, and Chrysler.  We were extremely excited that with the Ford 8.8” swap, we can use this limited slip diff in our RX-7.

We have used the Truetrac in many different cars, ranging from our Project Budget 400whp S197 Mustang Track Car, to daily-driven 600-800whp Mustangs, as well as a 540hp Roush Stage 3 Mustang that we finished 1^st in class and 3^rd overall in the grueling Tire Rack One Lap of America.  Needless to say, the Detroit Truetrac was actually a major driving factor in the decision to upgrade to the Ford Explorer 8.8” differential.

For more information, we went into extensive detail of how the Truetrac functions and performs in THIS ARTICLE on Project Budget 400whp S197 Mustang Track Car.

We bought this 2010 Explorer differential on Ebay for $250 shipped.  But any 2007-2010 Explorer diff will work.