Car Repair Question: Noise Diagnosis for Axle Shaft Bearings

Rear Axle Shaft Bearings

Luckily diagnosing axle shaft bearings does not come up very often, because the sounds they make can be mistaken for other drive train problems..

Even a noisy tire with choppy tread can be mistaken for a defective bearing. This article talks about rear axles, seals and bearings. Not to be confused with a standard hub wheel bearing that a rim and tire attach to.

Generally speaking front wheel drive vehicles have rear sealed hub bearings. they often contain ABS wheel speed sensors and can be expensive.

Rear wheel drive vehicles with pumpkin style differentials and solid axles have axle bearings. They are inexpensive but labor intensive to replace and diagnose.

Many vehicles go to the junkyard with the original axle shafts and bearings. If the rear differential is serviced properly and the fluid level is maintained, this will in turn lubricate the bearing.

Periodic inspection of your rear differential and checking fluid level is a good maintenance routine to get into and can save you a lot of trouble as the automobile ages.

Some of the key areas that fluid can leak from are the rear differential pinion seal as well as the axle seals.

When axle seals begin to leak the heavy gear oil can be dispersed onto your rear brake shoes or pads and rotors or drums. This can reduce braking efficiency as well as create noise and possibly a burning odor.

Types of Axle Shaft Bearings

There are three major bearing designs used in cars and trucks. There is a ball type, straight roller and a tapered roller style.

Regardless of the type utilized the main function is to support the vehicle’s weight, reduce rolling friction by allowing the wheel to spin freely.

A visual inspection of the bearing in most cases is not possible until you slide the axle out of the differential housing. In some cases its obvious how the axle is held into the differential housing.

In many Ford applications you will see bolts that hold a flange against the differential tube. Removing these bolts allows the axle to slide out. On GM vehicles it is more common to have the shaft retained in the differential carrier.

On these types of set ups you have to remove the differential cover then remove the pinion shaft. Next push the axles towards the center to reveal and remove a C clip retainer.

With the C shaped clips removed they will easily slide out of the differential housing. When replacement is needed, often the axle bearings are pressed onto the shaft using special equipment and holding fixtures.

Many auto parts stores will provide this service for free if the replacement parts are purchased at the store. You should also replace the axle seals at the same time. The parts store shouldn’t let you walk out the door without new seals.

Diagnosing Bearing Failure

With the axles removed as described above you can perform a visual inspection of the shaft bearings and look for scoring, burn marks or even pitting or chips on the individual rollers.

Most often when lack of lubrication causes bearing failure you can actually see heat damage in the form of bluish or purple marks on the rollers.

When it comes to diagnosing defective parts in any drive-train system a good diagnostic road test should be performed before dis-assembly occurs.

This can often point you towards a suspect part. It may also eliminate other items that can be mistaken for axle shaft bearing noise. Bad axle bearings often make a growling or rumbling sound at highway speeds.

Changing lanes may cause the noisy bearing to either increase or decrease the noise level. An example is if you are in the center lane and you move to the left lane.

Additional weight is put on the right rear. An increase of noise from the right rear during that lane change may indicate an inspection of the right side is necessary.

These types of lane changes and diagnostic methods should only be used in a safe manner. Preferably on a quiet road way with no other traffic around you.

Making drastic lane changes could be considered reckless driving and an accident is highly possible. It wouldn’t make any sense to wreck a perfectly good vehicle just to find out what bearing is noisy.

HOW TO FIX BLACK SMOKE?

HOW TO FIX BLACK SMOKE?
Begin with the vehicle on level ground, parking brake set while wearing protective eye wear and glove

Step 1 - If the check engine light has illuminated the PCM has detected a malfunction that could be causing the black smoke such as a shorted fuel injector

Step 2 - When a fuel pressure regulator fails it allows raw fuel to enter the engine producing black smoke.

Step 3 - A stuck or shorted fuel injector can allow too much fuel to enter the engine.

Step 4 - Occasionally a computer can malfunction holding the injector drivers open longer than it should, causing an excess of fuel producing the black smoke.

Step 5 - A bad computer system ground can lead to a malfunction that can include allowing too much fuel to enter the engine producing black smoke, inspect wiring harness grounds at the battery and engine.

Step 6 - On older engine's inspect under the hood for vacuum leaks which can cause the computer to malfunction creating black smoke.

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HOW TO FIND A VACUUM LEAK?

Easy step by step guide on how to detect and fix an automotive engine vacuum leak, this information pertains to most vehicles.

Begin with the engine cool on level ground with the emergency brake set, also wear protective eye wear, gloves and clothing. Carburetor cleaner is flammable so use caution when testing, have a fire extinguisher ready. (Note: Never spray exhaust manifolds.)

Step 1 - Inspect vacuum hoses for dilapidation or cracks, this will cause the engine to stall, idle poorly and hurt gas mileage.

Step 2 - Vacuum lines can become hard due to under hood temperatures which produce an unwanted vacuum leak.

Step 3 - After removing the old vacuum line and check for blockage, install a new replacement hose, this can be done by using vacuum or fuel hose.

Step 4 - If after inspection, no broken vacuum lines are found carburetor cleaner can be used to further inspect for leaks.

Step 5 - After starting the engine and allowing it to idle, spray the cleaner near and around the throttle bore gasket, if the gasket has failed the engine will react to the spray by increasing the engine idle speed as the cleaner is burned. If the engine is idling rough it will temporarily smooth out as the cleaner is consumed

Step 6 - Continue testing by spraying around the intake manifold plenum and base gaskets while observing engine speed, if the gasket has failed the engine speed will increase.

Step 7 - Moving on to external components such as EVAP control solenoids, valves and connections while still observing engine speed.

Step 8 - A large amount of vacuum is used to work the brake booster and can allow major leaks, spray around the booster while observing engine speed. Also, an audible hissing noise can sometimes be heard coming from around the brake pedal when the brakes are applied which also indicates the booster has failed. An alternative method of a vacuum leak inspection is to pinch a supply line to the accessory and observe engine speed, an increase indicates a leak.

Step 9 - Check small vacuum tubes for cracks and broken pieces, these tubes provide vacuum to many accessories such as the heater/air conditioner, leaks under the dashboard near the heater plenum can also occur.

Step 10 - Use a small piece of vacuum line to act as a connector which will repair the issue and return the heater/defroster/air conditioner to it proper operation.

Step 11 - A vacuum gauge or tester can be used to check an external system for additional leakage. This is done by disconnecting the vacuum tube from the vacuum source (engine) and attaching it to the tester. Pump the tester and observe the vacuum, it should hold vacuum if the system is working properly. (Note: A small amount of seepage is normal.)