Selling Services: Wheel Bearing Hub Unit Q&A
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Selling Services: Wheel Bearing Hub Unit Q&A

Can I use an impact wrench to remove or install a wheel bearing hub unit?

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While it may appear to be easier to use an impact wrench, it is not recommended. We recommend the use of a certified, calibrated torque wrench. Impact wrenches can damage the wheel speed sensor. It can also create a false sense of security when adjusting a nut or bolt, which may be under or over torqued. This can leave a hub assembly susceptible to failure.

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What types of noise will a bad wheel bearing hub unit start to make?

The first symptom of wheel bearing trouble is usually noise. A rumbling, growling, chirping or cyclic noise of any kind from the vicinity of the wheels is a good indication that the bearings need to be inspected without delay.

Wheel bearing noise is usually proportional to vehicle speed, and does not change when accelerating, coasting or decelerating (which distinguishes it from differential, transmission or U-joint noise). The noise may change when turning, or become louder or even disappear at certain speeds. But it shouldn’t be confused with the clicks and pops produced by a worn or damaged outer CV joint on a FWD car. A bad outer CV joint usually only makes noise when turning, not when driving straight ahead.

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What should be done if the splines are damaged on the axle shaft?

Nothing really can be done to the shaft except replacement. Damaged splines can cause damage to the new bearing. When installing a new hub unit, check the positioning of the splines on the axle shaft as the hub assembly is inserted into the knuckle. Carefully position the two components so the splines are not damaged during this process. Never force the hub assembly on the shaft or strike with a hammer.

The new wheel bearing hub unit I am installing has new wheel studs, should I lubricate them?

Never use lubricants or penetrating fluids on passenger vehicles’ wheel studs, nuts or mounting surfaces. Wheel nuts, studs and mounting surfaces must be clean and dry. Lubricants on the studs can cause inaccurate torque settings and damage to the threads. A thin layer of moly-lube may be used on the inner mating surface of the rotor where it meets the hub to slow down corrosion.

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Why are more vehicles using hub assemblies?

Hub assemblies are unitized, maintenance free and non-serviceable units that are preset, pre-greased and pre-sealed, easing installation and increasing product reliability for enhanced performance. These hubs require no maintenance or handling, which eliminates the need for preventive maintenance, grease and/or future adjustments.

How much runout on the rotor’s face can rust cause?

Rust on the hub’s mating surface is a leading cause of runout. The rust can form to a point where it actually pushes the rotor away from the hub even with the wheel bolted on. This process has been termed “jacking.” As little as .001” of rust at the outside edge of the rotor will result in .002” to .004” of runout when measured at the outside edge of the rotor.

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Can I replace the bearings or seals in my hub assembly?

No, because the hub assemblies are unitized, maintenance free and non-serviceable. Most hub assemblies are designed with a unitized bearing or flange that is intricate to the hub and/or bearing housing, which are not replaceable.

What happens when the wheel speed sensor in a hub unit affects the ABS system?

If a sensor becomes damaged or has malfunctioned, the system is meant to revert to normal braking mode. This means the ABS system will shut down if trouble is detected. The wheel hub unit will continue to operate in its normal function. It is safe to drive on the hub unit, but the ABS system should be checked at your earliest opportunity.

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Since a wheel cannot be steered unless it is rolling, a locked wheel offers no steering control of the vehicle. ABS restores steering control by quickly applying and releasing pressure on the affected wheel or wheels.

What does bearing play have to do with air gap in the wheel speed sensor?

The tone ring on most hub units is on the internal moving parts. As the bearings wear out or are damaged, the air gap changes. In extreme cases, internal and external sensors can be damaged from excessive movement caused by too much endplay. This indicates a lack or loss of bearing clamp. This normally results from severe mechanical break up or damage.

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The internal tone rings can be mounted on a variety of surfaces. Some newer units use a magnetic impulse ring for ABS that is part of the seal of the bearing. This ring does not have teeth, but instead it has small magnetic regions embedded in the side of the seal. To make sure what side the impulse ring is located, one can use a thin, light metallic object that you carefully place against the side of the bearing. The magnetism from the bearing will attract the object. Mount the bearing with the magnetic impulse ring toward the inside, against the ABS sensor. Be aware that incorrect mounting can lead to failure of the braking system to function properly. Don’t let the magnetic impulse ring be subjected to hits and bumps or make contact with other magnetic fields.

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Is it possible to repair or splice wheel speed sensor harnesses?

No, it is very difficult to repair wheel speed sensor harnesses. The harness is in an environment that is exposed to water, heat and flying debris. The voltages measured by the next generation of wheel speed sensors are so small that an alteration in the wiring can cause problems. This can lead to even more ABS diagnostic codes being set.

Is it permissible to use a replacement bearing with impulse wheel on a vehicle that does not have ABS?

Yes, a bearing with impulse wheel can be used on both ABS and non-ABS applications. In the cases when the car does not have ABS, the impulse wheel is there, but is not used. It does not affect the function of the bearings.

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What triggers an erratic signal code in a wheel speed sensor of a hub unit?

Understanding the two types of systems currently in use will help understand what triggers an erratic signal code.

Type 1 or “Passive System” uses a couple different types of impulse wheels. One of the most common is the gear-toothed style. This is usually pressed on to the back of a hub unit or CV shaft. A sinusoidal signal is created as the gear rotates past the magnetic sensor. The magnetic senor is usually bolted to the knuckle of the vehicle and the wiring is routed to the ECU. The toothed portion of the gear creates a high magnetic flux and the open portion causes the magnetic field to breakdown.

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This open type of system is susceptible to grit, dirt, water, heat and vibration. All of these can cause problems and trigger an erratic wheel speed sensor code. After verification of the trouble is complete, a good visual inspection should be done.

Type 2 or “Active System” uses an integrated sensor and magnetized impulse wheel built into the carrier portion on a hub unit. These systems are less susceptible to the environment, but they can break down internally either mechanically or electrically. If this occurs, an erratic signal code can be triggered.

In both types of systems, all connections should be checked to make sure they are clean and tight. Wiring needs to be checked to make sure it is routed correctly. A stretched or pinched wire can break down internally. If you are routing a new sensor, make sure all the connectors are utilized.

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If the cord is going through the knuckle on the vehicle, make sure it is placed through the gap in the knuckle made specifically for the ABS cord. Testing should be done following the manufacturer’s guide lines for that specific vehicle. An oscilloscope or DVM may be needed along with an ABS scanner.

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