Double-Eight Rebuild: New Life For A 26-Year-Old Ford 8.8-Inch Axle

DOUBLE-EIGHT REBUILD

Bruce W. SmithPhotographer, Writer

“My mama always said life is like a box of chocolates. You never know what you’re gonna get.”

Forrest Gump’s philosophical words were on our mind the moment Mobile Diesel Service tech Matt Johnson removed the last bolt holding the dirt-and-rust-coated cover on our 26-year-old Ford Bronco’s rear 8.8-inch differential. When the gear lube first poured out, we were elated to see it was clean and free from any obvious signs of heavy gear wear or broken bits. Then one of those chocolates that taste bad popped up as Johnson set aside the cover. The ring gear looked OK, but the spider and side gears were discolored and had a bad case of “crow’s foot.” The damaged gears would have broken under the first good shock load on the trail. Disappointing, yet not totally unexpected on a Bronco differential with more than 200,000 miles on it.

Gearing Down For Power

Although a rear diff rebuild wasn’t in the original game plan for this rig’s mild trail tune-up, it will work out for the best in the long run. The Bronco is fit with 33-inch tires, and with the stock 3.55:1 gears and 5.0L V-8 there’s not much power down low. The stock open differential makes traction in slippery situations an added concern.

The good news is that the aftermarket has the parts needed to rectify our Bronco’s woes. We contacted G2 Gear & Axle and the company sent us a 4.10:1 ring-and-pinion, Ford 8.8 Master Installation Kit, and 31-spline axleshafts. We addressed traction issues by giving Eaton a call to procure a Posi limted-slip differential.

The 4.10s will offset the taller tires, giving the Bronco the equivalent of 3.73:1 gearing. That’s a good ratio for everyday driving and light-to-medium off-road use. The G2 axleshafts will be a vast strength improvement over the OE ’shafts. The Eaton Posi will provide good traction for all-around use on- and off-road without breaking the bank.

Addressing Small Details

Those rebuilding Ford pickups and Broncos that have the early ABS system (mid-’80s to ’91) will also need to be diligent in checking over the reluctor gear tone ring on the differential carrier and the vehicle speed sensor (VSS) mounted in the top of the pumpkin. These older Ford trucks had drum brakes on the rear, discs up front. The ABS, along with the operation of the E4OD automatic and speedometer/odometer, are tied into the signals received from the VSS that’s reading the rotating speed of the tone ring’s teeth passing beneath it. So when it’s time to rebuild the double-eight, it may be prudent to install a new sensor and tone ring so the ABS and automatic work harmoniously.

Another little detail is to have new bearings and seals on hand to replace the old ones. The seals and bearings in older Ford axlehousings tend to wear a groove in the axleshaft, creating both a potential weak point and a leak point. If you aren’t replacing the axleshafts, an easy fix is to replace the normal traditional seals and bearings with axleshaft repair bearings. The repair bearing combines both bearing and seal into one part and moves the position of the bearing and seal outward so they ride on an unworn section of the old axleshaft.

Parts in hand, we turned to Johnson’s expertise on putting our Bronco’s ABS-equipped 8.8-inch axle back into trail-ready, daily driver shape. Read on for some valuable tips we learned along the way.