Tips And Tricks For Regearing Ford’s TTB Dana 44

    Geared Up

    Bruce W. SmithPhotographer, Writer

    Gearing is the cornerstone to performance on-road and off. The numerically higher the axle ratio, the better the response to throttle input and the quicker the acceleration. Most wheelers know that and choose the axle ratios in their 4x4s accordingly when they purchase a new rig, opting for ratios like 3.73s and 4.10s over “taller” gears like 3.08s or 3.31s, which are meant for highway cruising.

    Many choose 3.55s, the middle ground in gearing. All is well in that respect until it comes time to add a lift kit and taller tires. Increasing the diameter of the tires by 3 inches has the same effect as changing the axle ratio say from 3.73s to 3.42s or, in the case of our Bronco, 3.55s to 3.31s.

    Stepping up to tires that are several inches taller than stock doesn’t take nearly as much of a performance toll in today’s newer fullsize 4x4s as it does on those built 20 or so years ago. That’s because the V-8s in today’s trucks and SUVs generate nearly twice the horsepower and torque as the same size engines offered back in the ’80s and ’90s. On top of that, 4x4s back in that era used four-speed automatics, while today, we have five, six, and eight speeds. Gearing is everything.

    Regaining Lost Performance

    That brings us to rebuilding the front differential in a ’91 Ford Bronco. Its 5.0L engine and A4OD transmission really felt the power drain when a set of 33s were slipped underneath. The factory 3.55 gears, which were fine when the Bronco was running stock tires, just didn’t cut it for our intended use with the taller, meatier Pro Comp treads.

    Recently, we swapped out the gears in its 8.8-inch rear differential for 4.09s and upgraded the open diff with an Eaton Posi. Then it was the time to face Ford’s Twin-Traction Beam (TTB) front differential that is found under ’80-’96 Broncos. It looked intimidating, but we soon found tackling the job wasn’t nearly as bad as we thought it would be, thanks to a few tricks Mobile Diesel Service’s Ruben Villalobos showed us as he went through the rebuild process. Yes, Mobile Diesel Service does more than just diesel tech.

    Carrier Breaks

    There’s one nuance to be keenly aware of when it comes to changing gear ratios in this era Ford truck, be it Bronco or F-series, as we learned from the techs at G2 Axle & Gear. The high-pinion Dana 44 uses two different ring gear carriers depending on the axle ratio. This is referred to as a 3.73/3.92 “carrier break.” This is important to remember because some DIYers have overlooked the carrier differences and installed the new gears, only to find the ring gear barely touches the pinion.

    Carrier breaks are common. What happens is as the axle ratio increases numerically, the ring gear typically remains the same diameter while the pinion gear diameter gets smaller. At some point in changing gear ratios, keeping the two in contact means the ring gear has to be made thicker—or the ring gear mounting flange, called the deck, must be moved closer to the smaller pinion gear.

    To change from 3.55s to 4.09s, like we wanted to do, required using the 3.92-and-up carrier, which placed the ring gear 0.320-inch closer to the centerline to make up for the lower axle ratio’s smaller pinion diameter. G2 Axle & Gear had both the carrier and the master rebuild kit to make the gear swap easy.

    TTB Diff Removal

    Removing the differential from the Ford TTB is actually pretty simple when you think of the components. The driver-side beam is also the cover for the third member. To remove it, you have to slide out the axles. The driver-side axle is held in place by the spindle, so it easily slides out of the Dana 44 once the spindle is removed. However, the passenger-side axle is two-piece, with the outer half held in place by the spindle like the driver side. The inner slip-shaft is held in place by a C-clip on the inside of the differential, and it can only be removed once the third member is on the work bench.

    Knowing this made the removal, regearing, and rebuild of the TTB Dana 44 a lot easier than we first imagined. Thanks to the expertise of both G2’s tech support staff and our mechanic friend Villalobos at Mobile Diesel Service, our big Bronco is going to feel a lot stronger when we hit the trails and backcountry roads this winter with the right axle ratio helping put the power down.

    Tapping For Oil

    Sometimes it’s handy to be able to drain the oil from the front differential. With the Ford TTB Dana 44, to do so requires unbolting the third member from the driver-side beam that serves as the diff’s cover. This is not handy at all, so we drilled a 37/64-inch hole through the bottom of the housing, tapped it for a 3/8-inch pipe plug, and installed a hex-head plug so we could easily drain the oil. We didn’t tap all the way through so the plug would stop just before it was flush with the housing, and it couldn’t work its way into the diff itself. Now we can drain the oil by simply using a standard 3/8-inch hex wrench.