The Dynatrac Free-Spin Hub...
The Dynatrac Free-Spin Hub Conversion Kit for the Ford 4x4 Super Duty and Dodge Ram comes complete with all bearings, seals, and replacement spindles, hubs, and stub axles.
The unit bearing was a great engineering breakthrough. Imagine the time it once took to set up and properly adjust the front hub bearings on big Ford and Dodge 4x4 trucks on the assembly line. A unit bearing is all neatly packaged and sealed-no mess, no greasy fingers. Plop it in, tighten a few bolts, and send the truck down the road. However, as with all new things, there were bugs.
No Service
Unlike older front hubs/bearings, these sealed units cannot be serviced, and they have been known to fail without warning. When they die, the damage can be extensive. The replacement bearings alone can run about $400, plus new studs, nuts, an external O-ring seal, and labor. If it's not caught in time, the rotor, spindle, calipers, brake pads, and the stub axleshaft-basically everything in front of the galvanized brake dust plate-are history. All this can happen in just half a mile when you are driving 65 mph!
The inner and outer bearings...
The inner and outer bearings in the OEM hub are stacked right together, which decreases their mechanical ability to absorb the leverage. The Dynatrac design is much stronger, and the bearing cage is steel.
Better Bearings
Bearing maker Timken told us its bearings are engineered to have an expected life of 150,000-200,000 miles. That's quite a spread! In fact, the front hub bearings in our own Ford F-550 Super Duty failed at something under 10,000 miles. With heavy loads and/or bigger tires, failure rates increase. However, many people who appear to be using their Super Dutys or Dodge Rams under normal conditions (stock tires and light-duty use), have experienced failures within the first 50,000 miles. Unit bearings are often considered to be a "normal wear" item and, therefore, are not covered by warranty at any mileage level. Some dealers may approve this type of work under warranty on a case-by-case basis, but one-time repairs at a dealership can easily exceed $1,500.
The pre-assembled rotor, dual...
The pre-assembled rotor, dual wheel adapter spacer, and the new hub combine to make a rather heavy part to lift and slide over the spindle later, especially on F-550 and F-450 models. Individual components can be fitted one at a time to the steering knuckle.
Warning Signs
There are some signs to look for that may indicate your wheel bearings are close to failure. If the ABS light comes on and stays on, it may mean the tone ring located between the two sealed wheel bearings is wobbling. If this happens, immediate inspection is a good idea. Excessive heat and/or uneven brake pad wear is another sign of problems. The old jack-it-up-and-wiggle-the-wheel method can also tell you if something is amiss. Also, check if overheated grease is seeping out from the seal. You can also spin the wheel and listen for a grating noise. But you have to do something before the bearing fails-none of these tricks is much help when you're stranded on the side of the road with a truck that won't move.
The Fix
Fortunately, now there is a solution. Dynatrac has designed a "fixed spindle" unit that is far superior to the factory "live spindle." This is similar to the serviceable hub and bearing assemblies we have known since the early 1980s. The new spindle is forged from chromoly steel, and a cast nodular wheel hub replaces the OEM unit. The kit also uses Warn Premium manual locking hubs to engage or disengage four-wheel drive (a definite upgrade for Dodge drivers, who lost manual hubs after the '93 model year).
The new spindle is forged...
The new spindle is forged from chromoly steel. This is a traditional fixed spindle. The new hub rotates around it.
Dynatrac engineers also upgraded the OEM 1.31-inch, 30-spline outer stub axle to a stronger 1.50-inch, 35-spline unit. The conversion uses all stock components-rotor, caliper, and brake pads-and is fully compatible with the stock ABS sensor. The Timken bearings, races, and seals are the same as those used on '86-'97 F-350 4x4 trucks and are also common to many Dodge and GM 4x4 trucks. The parts can be purchased at any parts house for about $65 and can be inspected, repacked, and adjusted as part of normal service.
After experiencing bearing failures on two occasions on our '99 F-550, we took the opportunity to visit the Dynatrac facilities for a close-up look at the new conversion kit and the installation process. The owner of Dynatrac, Jim McGean, explained that the sealed OEM unit bearing had several problems. First, the two bearings are stacked right together, which decreases their mechanical ability to absorb the leverage exerted by the wheel. On dualies, this is compounded by the large dual rear-wheel spacer/adapter installed on the front axle, further increasing the leveraged force on the bearings. While the bearing may come from the factory properly greased and torqued, the sealed units cannot be inspected, adjusted, or serviced, so when the seal begins to leak or any contamination gets in, the bearings can overheat, causing more grease to escape. All of this is further aggravated by the fact that the bearing cage in the OEM unit is plastic, not steel. Once extreme temperatures are reached, the cage melts and total failure is rapid and complete.