Although the 8.8-inch rear axle found under zillions of 5.0L and 4.6L Ford Mustangs is a pretty good piece right from the factory, there are a couple of drawbacks: a dismal selection of factory gear ratios (ranging from 2.73 to 3.27) and somewhat weak 28-spline axles. We found out just how easy it is to improve upon these drawbacks when we recently purchased a 8.8-inch rear-end for a 1985 Mustang GT with a five-speed.
Our GT’s original 7.5-inch axle was marginal at best, even for the stock 210-horse 5.0L under the hood. The 2.73 gear and lack of a positraction unit made the situation even worse. We chucked the 8.8’s tired stock innards (Traction-Lok differential, 3.08 gears, and axles), sandblasted and painted the housing, then stuffed it with a brand new Eaton Posi Performance differential, Superior Axle 3.55 ring and pinion and 31-spline axles, and a deluxe rebuild kit from Ratech. Ratech also supplied one of its very trick solid pinion spacers, which we think is a must-have for a serious 8.8.
The fruit of our labor is a rear axle ideally suited for our streetbound Mustang. The 3.55 gears will vastly improve the GT’s acceleration without putting a serious hurt on highway cruising and gas mileage. The Eaton Posi and Superior 31-spline axles are more than capable of handling the power of our stock five-oh-and are capable of taking lots more if we decide to turn up the horsepower wick. Follow along and we’ll show you how to add some kick to an 8.8 axle.
|SAG-F88355||Superior Axle Ring and Pinion Gear Set, 3.55 ratio|
|ETN-19588-010||Eaton Posi Performance Differential, 31-spline|
|RAT-305K||Ratech Ring and Pinion Installation Kit|
|RAT-4104||Ratech Solid Pinion Bearing Spacer|
|SAG-EV81||Superior Axle Evolution Series Axles, 31-spline|
|SME-8510500||Summit Racing Aluminum Differential Cover|
No Ford axle has “positraction”. That is the term for GM’s factory limited slip.
Make sure you also weld the tubes to the center.