Wednesday, May 23, 2018

Check Wheel Bearing Noise By Rotating The Wheel

Worn out wheel bearing will make a noisy sound, like a humming sound or even rumbling. Sometimes it is difficult to find which wheel has a worn out bearing.

One way to find a worn wheel bearing is to rock the wheel by hand. Jack up the wheel, grab the top and bottom (12 and 6 o'clock) of the tire by hands, then rock the tire like arrows in the above picture. If the wheel moves like wheel nuts loose, then it has excessive end play, and possibility of bearing worn out.

For the rear wheels can also be grabbed at 9 and 3 o'clock position. But for the front wheels where there is a steering system, test result can be confusing. Because when the wheel is rocked, end play in the steering system will make the test result confusing.

But in this case, there is no wheel with excessive end play found. So the bearing is tested by rotating the wheel directly by hand, after the wheel is jacked up.

This vehicle has FWD (Front Wheel Drive) system. So the rear wheels can be easily rotated by hand. The test results indicate that the left rear wheel has a worn out bearing, because it is humming when rotated.

In the video above, the bearing produces humming sound at a speed of about 70 km per hour, before being repaired. Then the humming sound disappears after being repaired, when tested at the same speed.

The video also shows the rotated left rear wheel. It produces humming sound, before it is repaired. Once fixed the humming sound disappears, and the wheel rotates more slowly due to the tighter new bearing.

Today wheel bearing is also equipped with magnetic ring to determine the speed of the wheel for ABS (Anti-lock Braking System). And many manufacturers make these bearings. So it needs a practical way to test the strength of magnetic ring before buying it. The following video shows how to test magnetic ring easily.

Sometimes the sound of the tire can also make confusing. By jacking up the wheel, and turning wheel by hand, it can be distinguished whether the noise is coming from the tire or from the bearing. If the wheel is not noisy when rotated by hand, it means the noise is coming from the tire, not from the bearing.

A worn out tire tends to make a humming sound. For sedan car, moving the worn out tire from the front to the rear can reduce the humming noise.

In addition, the front wheel bearing is also equipped with magnetic ring. The video below shows another way to test the magnetic ring.


  1. Hi

    Good info

    I have ABS light on. Autel scanner told me front wheel driver side - sensor needs cleaning.Fitted new sensor but this did not fix it and i cant find anything magnetic. Do you know if the bearing is the reluctor or the bearing seal..?

    Car is 2003 CLK 2.7CDI

    If you can help pls email me:-


    1. Hi Tony..Before blaming wheel bearing magnets are producing low signal, ensure wiring harness is still good. It can be damaged by dirt and stone thrown by tire. The harness also can be worn out or cut because it is at the front wheel which can be turned to left and right. Open the wire loom and check wire condition. Disconnect sensor and check voltage from the control unit harness when ignition switched on. It is a small DC voltage, compare to other cable harnesses.
      Some sensor can be checked by turning the wheel by hand and producing alternating current. The output voltage of sensor is about 0.1-0.2 VAC, when the wheel is turned by hand. Compare the output voltage to other sensors, to get the standard value for your car (Mercedes Benz Diesel CLK 2.7 CDI 2003).
      Higher wheel speed will produce higher voltage. If you dont have sensor tester, the voltage test can be done with a volt tester with long probe wires. Connect the sensor to volt meter, you may need and small alligator clips or special connector to do it. Drive the car to check the output voltage. Or jack the wheel and run the wheel by engine, if it is the driving wheel, for your car is the rear wheel.
      The reluctor ring is rarely damaged, it is usually dirty. The magnetic field can be obstructed by dirt, so it needs cleaning.
      The bearing seal cant be replaced, because it is integrated with the bearing.
      I hope this will be helpful for you.
      Rgs, Heru.

    2. Hi Heru and thanks for your reply..

      Being an Electronics Engineer i did test the wiring and sensor. With my Fluke 87V on ac mV the sensor produced no output. I then measured the sensor resistance and got an open circuit. At this point I changed the sensor for a new one but it wasn't an OEM sensor and measuring it's resistance gave me 48k ohms which is higher than some internet sources give sayoing it should measure between 1k & 2k ohms.

      I then removed the wheel hub to get at the rear where the sensor picks up the magnetic encoder. The rear bearing seal was very dirty so i cleaned it thoroughly and then tested with a small ferrous pin suspended by a thread. There seemed to be no magnetism present.
      Since then I have purchased a set of new front wheel bearing kits which are complete with rear seals.. which btw are separate to the bearing. They haven't yet arrived.
      I have also purchased a small magnetic field tester which will prove invaluable to test the old and new bearings which i have been told house the magnetic encoder. Will know for sure when they arrive and will keep your blog updated with what I find..

      As a final note.. I re-tested the old removed sensor again when I was inside that evening and it did show a high resistance and give a 1.2mV when i passed a magnet close to the sensor end.


    3. Hi Tony...Sounds like you have already done a correct procedure. I’m wondering about weak magnetic field. Because usually magnetic field is weaken by heat. Looks like the closest heat sources in that area are brake and bearing. Can brake and bearing heat weaken magnetic field?? Again.. You have done the right thing to purchase magnetic field tester.

      You are correct about the rear seal of your Mercedes, it is separated from the bearing. I was confusing with integrated type of bearing, like the one in my articles. Thanks for correction...

      Im looking forward for progress and result of your car repairment, hopefully the problem will be solved soon.

      Rgs Heru.

    4. Hi again Heru..

      Well the new bearings arrived and I could see the magnetic encoder is attached to the rear bearing seal metal casing. Using the magnetic field tester I can clearly see each little magnet on the encoder.
      Seeing the new seal it was immediately apparent that my magnetic encoder was missing from my seal..! This is where the importance of the brake disc dust/splash backplate's condition becomes more apparent and important. Mine was corroded and bits had broken off. Perhaps one of those corroded bits came off and hit the magnetic encoder and completely disintegrated it.. because it is completely gone. So I think this explains the ABS failure which also makes ESP BAS & Cruise Control inoperative and brings on the Check Engine light.
      I need to now purchase new disc dust/splash covers but so far am finding they are more expensive than the pair of bearing kits !

      Stormy weather here and I don't have a garage so have to wait until the rain and high winds are gone.
      I'm optimistic tho' ;-)
      Will probably fit the original sensor back because it is OEM.
      Will keep you informed..


    5. Hi Tony...Now you already have gotten the clue about what was happening.
      While waiting for brake dust shield, now is a good time to plan carefully what to do, and prepare tools for brake dust shield and bearing removal and installation. Be patient, make no mistake.
      When I was working at mining site, we used service car and tarpaulin to work at pit when raining. Service car was parked at certain position to the repaired mining machine and attach tarpaulin in between as a roof. It was not very easy to go back to workshop or warehouse if something forgotten. While that mining machine was needed to work immediately. Good planning is the key for situation like that.
      Good luck n hope to hear you enjoy driving your Mercedes soon.
      rgs Heru.


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