Car wheels turning at 800 revolutions per mile can generate a lot of friction and heat. Wheels spin freely without generating excessive heat while supporting the weight of the vehicle with the help of Roller-type or ball bearings packed in grease inside all four wheel hubs. In addition, they improve fuel economy by reducing friction.
While some wheel bearings need fresh grease periodically, most wheel bearings are sealed and don’t need regular maintenance. They typically work more than 100,000 miles. Bearings get damaged when hit by potholes or curbs or in an accident.
They also fail when seals wear out and allow grease to escape and dirt and moisture to enter. When they fail, they make a roaring/rumbling noise. The entire hub assembly must be replaced when the bearings fail on vehicles with sealed bearings.
What Causes Bearing to Fail?
The contracting metal, air, and lubricant create a vacuum when a bearing is cooling off after use that is hopefully held by the seals. In case the seals can’t hold the vacuum, the bearing/sealed hub unit will sip the outside air, debris, and water. In some parts of the country that use salt on the roads, it becomes as bad as ocean water on wheel bearings.
The components wear and possibly change their metallurgy when these contaminants circulate through the grease and between the races and bearings.
A driver may notice the following things –
– Some steering wander/looseness in the steering maybe a noise coming from the vicinity of the wheel
– Abnormal tread wear on the front tires.
The noise may change when turning, or become louder or even disappear at certain speeds coming. This noise should not be confused with the clicks and pops produced with a worn outer CV joint on a FWD car. A bad outer CV joint mostly makes a noise when turning, not when the driver is driving straight ahead.
Once a bearing is worn out, the wear rate augments by seals that no longer can keep out the contaminants, and heat which has been increased may breakdown leading to
Usually, a bearing wears out due to the following reasons
– Inadequate lubrication
– Faulty installation
– Improper adjustment.
For a successful repair, you need to determine why the previous bearing failures took place. It is impossible for sealed hub units to examine the internal bearings and races.
Determine what kind of roads the car is driven on. Also, what types of loads are being carried. If you overload the vehicle, bearing damage can possibly be inevitable.
Most common failure pattern for bearings is for those sitting on the passenger side of the vehicle as the passenger side bearings are exposed to most of the standing water in the gutter. Even if the bearings on the driver side of the vehicle fail first, take a close look at the passenger side bearings, failure may not be far behind it.
Most of the bearing components are heat-treated to harden the metal. But, we need to see that the heat-treating can only penetrate so far into the metal. Once the bearing has worn out through this particular layer, rapid and catastrophic wear hits the softer metal below. This kind of fatigue failure is called “spalling.” This type of damage makes the metal to come off in form of flakes.
If a bearing gets overheated, the hot lubricant will break down and might cause scoring and even etching of the bearing surfaces. Also, water and other corrosive elements might create such a condition, which will lead to spalling down of the road. Burned/oxidized lubricant might leave behind a dark coating on the bearing surfaces. Remember one thing, tapered roller bearings, excessive pre-load can mimic the same damage. If a bearing is getting really hot, cages and seals could be deformed and lead to a bearing lock-up.
Seals are critical for the longevity of a bearing. If contaminants find some way in, they could cause a wear pattern known as bruising. Never re-use seals. Used seals can leak and will contaminate brake linings or can lead to premature bearing failures.
Bearings are said to be precision products that need complex manufacturing processes. Inferior bearings using low-quality steel and having poor heat-treating can lead to
Over tightening and adjustable tapered roller bearings is usually a common error that can lead to a premature failure. Tapered roller bearings lying on the front of RWD vehicles are never preloaded. They’re snugged up with no more 15 to 20 ft. lbs or less than that of torque while the wheel being rotated to make sure the bearings are seated. Then the adjustment nut is made loose by 1/6 to 1/4 turn, and then it is made locked up in place with a new cotter pin. Rule says, endplay should be about 0.001 to 0.005 inches.
No play is allowed on most FWD cars, but sometimes up to 0.010 inch of play in the front bearings might be acceptable on RWD cars and trucks having adjustable bearings.
The FWD cars that got adjustable tapered roller rear wheel bearings, the bearing adjustment procedure is usually the identical with the RWD vehicles (zero pre-load), but some vehicles require a slight pre-load. Ford, for example, says that the rear wheel bearings on older Taurus models should be preloaded in a light manner, i.e., 24 to 28 in. lbs. (2 ft. lbs.).
How to Change Wheel Bearings
1. Park your vehicle on a surface which is flat.
As with most types of maintenance of the automobiles, you would want to take all necessary precautions while changing the vehicle’s wheel bearings to ensure one’s safety. The worst thing that can happen while changing your wheel bearings is for your vehicle to suddenly shift or it might roll away. Before you begin, make sure to park your vehicle on a level surface. Park your vehicle (or, for manuals, 1st, reverse, or neutral) and be sure to put the parking brake up.
- Note: Every vehicle is supposed to be different. The instructions below are intended to be a general set of guidelines and thus will not perfectly work for every vehicle. If you run into any problem while making an attempt to change your wheel bearing or have some doubt after you finish, it’s wise to use the help of a professional mechanic. It can help to save time, can prevent future headaches, and will save money in the long run.
2. Secure the wheels with wheel chocks whose bearings you aren’t replacing.
To add stability, it will be smart to use sturdy chocks which will hold your vehicle’s wheels in place. Obviously, you like to use chocks on the wheels you are not planning to modify, as the wheels you actually modify will be elevated from the ground. For example, you will place wheel chocks behind the rear tires if you are about fix a front wheel bearing and behind the front tires if you are about to work on the rear wheel.
3. Loosen up the lug nuts and lift the wheel with the help of a jack.
To make a proper access to the internal components of the wheel whose bearings you’re replacing, you’ll have to elevate the wheel. Luckily, most vehicles come with a jack just to satisfy this purpose. Before lifting the wheel, however, you may want to slightly loose the lug nuts using a tire iron, as breaking their initial resistance is quite hard without having the ground holding the wheel steady. After this, carefully and safely lift the wheel. If your vehicle doesn’t come with a jack, you may need to buy a suitable jack for your vehicle from an auto supply store.
To prevent a dangerous slippage, check that the vehicle is securely seated on the jack and that the jack is flushed to the ground before attempting to lift the wheel. Make sure the jack touches the vehicle on a sturdy, metal piece of that undercarriage, rather than touching the fragile plastic moulding, as the weight of the vehicle can damage the latter.
- Jack points of most vehicles are where the frame has extra
support to lift the vehicle. The best way is to check the owners’ manual to
learn how to position your jack in the best place.
- It is also extremely wise to use a safety stand for jack to add support in case the floor or scissor jack fails.
4. Unscrew the lug nuts to remove the wheel.
The lug nuts, which you should have already loosened, will come off easily. Remove these and put them in a safe place where you can easily find them. Next step is to remove the wheel itself which should come freely.
- Some people keep a track of the lug nuts just by removing the hubcap, turning it over, and making it as a sort of a “plate” to contain them.
5. Remove the brake caliper and by using a socket and a ratchet, remove bolts of the calliper. Then, using a screwdriver remove the caliper itself.
- When removing the caliper, it should not dangle freely, as this
can damage the brake hose. Instead, hook it up on the secure part of the
undercarriage or use a short length of string to fix it in a place. Two
additional ways to secure the caliper are bungee cord or a bent wire hanger.
6. Remove three things –
– Dust cover
– Cotter pin
– Castle nut.
There should be a small metal or plastic cap called the dust cover in the centre of the vehicle’s exposed rotor which protects the components holding the rotor in place. Since you’ll remove the rotor, the cap and the components it protects will have to go. Usually, to remove the dust cover, grip it with calipers and tap the calipers with a hammer. Inside it, you’ll find a castle nut, which is usually secured with a cotter pin. Using pliers or wire cutters, remove the cotter pin, then unscrew the castle nut and remove it and its washer.
Remove the rotor. Place your thumb carefully on the peg present in the middle of the rotor assembly. Firmly (but somewhat gently) bump the rotor with the palm of your other hand. The wheel’s outer bearing should get loose or might fall out. Remove the outer bearing. Finally, remove the rotor itself.
- If the rotor is stuck, a rubber mallet can be used to hit it loose. This might damage the rotor, so it’s best to use a mallet only in the case if you are not planning on reusing the same rotor.
7. Unscrew the hub bolts to remove the old hub.
The wheel bearing inside the hub is usually held in place with several bolts that screw in from behind. These bolts can be tricky scenario to reach as they’re tucked away in the undercarriage, so you might want to use a skinny socket wrench and/or a breaker bar to make them loose and remove them. When the bolts are removed, take the hub off of the axle.
- Note that if you’ve purchased a new hub assembly, you can install the new hub and put the wheel back together and your job is done. To insert a new set of bearings into the hub, please read on.
8. Disassemble hub assembly.
To gain access to the bearings, hub needs to be taken apart. You will probably need to use a wrench (and/or a hammer) to remove the end of the hub and any other anti-lock brake wheel that may be part of that hub. Then, you might need to use a specialized “puller” tool for removing the central bolt. The bearing assembly should come apart easily with this process.
9. Remove the races and clean the knuckle.
Removing the bearing assembly’s races generally means physically breaking them with a grinder or with a hammer and chisel. As a result, you would want to have replacement races ready. After removing the races, cleaning the inside of the bearing assembly around the knuckle is a good idea.
- There would usually be lots of grease and grime here, so have plenty of rags as handy.
10. Install new races and new wheel bearings.
With a few taps from a hammer, set new races in place in the bearing assembly. Finally, grease for a new inner bearing and install it into the assembly. Ensure the bearings are in a proper alignment, they’re pushed in as far as they can go, and make sure any sealing rings are flushed with the outside of the assembly.
- Use large amount of grease for your bearings. You can apply the grease through bare hands or using a special “bearing packer” tool. Rub plenty of extra grease around the bearings’ outsides and any sealing rings.
11. Replace all parts in reverse order.
After you’ve changed the bearings, all that’s left to do is re-building your vehicle’s wheel. This actually means to install a new outer bearing after the rotor is in place. Hub assembly is put back together and installed on the axle shaft. Put the rotor back on and secure it with the bolts by re-installing them. Install a new, well-greased outer bearing. Then lightly tighten the castle nut and using a new cotter pin, secure it in place. Replace the dust cap and put the caliper and brake pads back in place and tight them with the appropriate bolts. Finally, put the tire back where it belongs and make sure to secure it with lug nuts.
- When you’re done, carefully lower the car back down to the ground with your jack. And finally you’ve changed your wheel bearings.