HUB UNITS

In the 1970’s, the twin blows of expensive fuel and inexpensive imports led the US auto industry to move to front wheel drive vehicles. Incorporating the front driving mechanism into the hub and suspension greatly complicated the adjustment and maintenance of conventional tapered bearing sets. This led to the development of the hub unit, an easy to install, pre-adjusted, and lubricated for life bearing assembly. These precision engineered, more expensive units had the advantage of a pre-adjusted internal clearance which minimizes wheel wobble, premium grease and seals providing maintenance free operation, and longer service life. Hub units come in 3 styles – Gen. 1, Gen. 2, and Gen. 3.

Hub bearing Gen. 1 – ABS/TCS

Based on a double row angular contact ball bearing, Generation 1 Hub is optimized for the special operating characteristics encountered on car wheel applications. The unit offers specific support the moment load is applied to the bearing during cornering. The main components, an outer ring and two inner rings, are matched with the ball set to give the correct clearance. The cages for the two ball rows are made from glass fiber reinforced polyimide. Gen. 1 is greased and sealed for life. Used mainly for driven wheels, Gen. 1 is also found in integral drum designs on the non-driven wheels of smaller cars. With assembly space at a premium, the very compact taper units (Gen. 1 T’s) are often selected.

Hub bearing Gen. 2 – ABS/TCS

Designed with the experience gained with Generation 1, Generation 2 has an outer ring with an integral flange, replacing the function of a separate hub. The flanged outer ring is designed as a lightweight structural component; outer ring raceways are induction hardened for bearing performance. The flange is tough with threaded holes or studs and a spigot to center and mount brake and wheel. The dimensions of the flange and spigot are to customer requirements. Gen. 2 is typically used with a rotating outer ring for non-driven front or rear wheels.

Hub bearing Gen. 3 – ABS/TCS

The third-generation hub bearing units carry a flange for wheel and brake rotor attachment and a second flange for fixing the unit to the suspension. This fully integrated system provides a significant simplification in corner design and handling when compared with more traditional designs. The dynamic load carrying capacity is maximized by the use of a separate inner ring for the inboard ball row. This ring is mounted with an interference fit. The outer flange is bolted to the suspension. The rotating inner ring, with its tough flange, spigot and threaded holes or studs, is designed for mounting of the brake and wheel. Gen. 3 is greased and sealed for life, and used for both driven and non-driven wheel applications. For driven wheel applications, torque is

transmitted to the inner ring via an involute spline.

Hub units – fitting guidelines

Fitting instructions for hub bearing replacement in passenger cars.

When mounting or adjusting hub bearings, it is extremely important for the safety of the vehicle, as well as for the operation of the bearings, that the shop manual for the vehicle concerned is followed in detail. Due to differences in car construction, the following guidelines are only of a general technical nature. When replacing bearings, it is essential that the correct mounting methods are used, that the proper tools are used, and that the clean procedures are observed in handling and installing all components, particularly the bearings. Do not open the bearing package until you are ready to install the bearing. Let the rust preventive compound remain in the bearing during mounting.

Gen. 1:

FWD Bearing Installation Guide

1. Loosen the axle nut while the vehicle is still on the ground. Do not re-use the old nut. Never use an impact gun on the axle nut.

2. To avoid damage to components, be sure to use the proper specialized pullers to remove the CV joint, hub and knuckle from the bearing.

3. Inspect all components for signs of fatigue or damage. Check bearing mounting bore for distortion or out-of-roundness. Any irregularities will improperly load the bearing and cause premature failure, so replace if in doubt.

4. Clean the bearing area in the knuckle and hub to facilitate smooth insertion. A light coating of lubricant can be applied to the knuckle cavity and hub to ease installation and inhibit corrosion.

5. When press-fitting the bearing into the knuckle, be sure to apply pressure only to the outer ring .(When pressing the hub into the inner ring, force must only be applied to the inner ring and the hub. The inner ring must not move in relation to the outer ring. The application of force to the wrong part of the bearing will render it useless by severely damaging the balls and raceways. After each step, check for binding or damage by rotating the bearings to be sure it turns smoothly. Press-fitting locks the bearing radially but to lock it axially, be sure to install the snap ring where required.

6. On older or higher mileage vehicles, consider installing a new CV Joint boot as a good preventive measure. Manufacturers recommend replacement after 60,000 miles.

7. Lightly lubricate and then carefully align the splines of the CV shaft with the splines of the hub to prevent damage. Using the proper tool, pull the axle yoke into the hub and seat against the bearing. Install a new axle nut, using the specific torque nut for that application. With the vehicle on the ground, do the final torquing to the OEM specifications. This assures the proper mating of the split inner rings of the bearing needed to achieve the proper internal clearance. (These torque specifications are now contained in the SKF Torque Specification Guide #457377). For specific mounting instructions, refer to the vehicle manufacturer’s service manual for that model.

Gen. 2:

FWD Bearing Installation Guide for rear hub

1. Lift vehicle and remove rear wheel(s). Remove axle nut. Check axle nut for any thread damage and replace if needed. Loosen adjusting nut on parking brake lever, if necessary.

2. Remove disc brake caliper from back plate and disc rotor from hub (if equipped with disc brakes).

3. Remove brake drum from hub and disconnect brake pipe from wheel cylinder (if equipped with drum brakes).

4. Disconnect ABS speed sensor if equipped. Remove hub-mounting bolts. Remove rear brake shoes, stabilizer bar or other components that may interfere with hub removal. Remove hub separating axle hub and bearing if needed.

5. Installation is done in the reverse order. Be sure mounting surface is clean. Check other components for damage. Make sure torque specifications are used for all components as needed, including hub mounting bolts and axle nut.

Note: Two piece axle and hub assemblies may need to be pressed apart.

Note: Some models equipped with ABS tone rings may need the tone ring switched over from the old hub unit to the new hub unit. For specific mounting instructions, refer to the vehicle manufacturer’s service manual for that model.

Gen. 3:

FWD Bearing Installation Guide for front hub

1. Lift vehicle and remove front wheel(s). Remove caliper and secure it aside.

2. Remove brake disc rotor. Remove cotter pin and axle nut. Check axle nut for any thread damage and replace if needed.

3. On models equipped with ABS, disconnect sensor connector if needed. Using steering linkage puller, loosen upper arm ball joint nut. Always be careful not to damage ball joint of toothed rotor (if equipped). Shift knuckle to outside to maintain clearance

between hub mounting bolts and drive shaft.

4. Remove hub mounting bolts. Remove front hub assembly. Check other components for wear.

5. To install, reverse removal procedures. Install mounting bolts and torque to specification. Slide CV shaft stub through hub assembly. Install axle nut and torque to specifications. For specific mounting instructions, refer to the vehicle manufacturer’s service manual for that model.

Hub sealing problems

The function of the seal is to keep the grease inside the bearing and to avoid the entrance of water, dust and dirt, which will cause corrosion and premature bearing failure. Appearance of a moderate amount of grease leakage is acceptable – this

helps protect the seal lips from external agents such as dirt.

Impact damage

All bearings are sensitive to shock and impact. You should never use a hammer in fitting a bearing. SKF recommends only proper fitting tools be used.

Remember, the wheel bearing is a safety component!

Also, before re-fitting the bearing in a knuckle, be sure that the bearing seat is clean and lightly lubricated.