Wheel bearings, for instance.
Properly greased and adjusted, they quietly do their job – which is to keep hubs and the wheels bolted to them turning (and rolling) smoothly on their spindles; axles rotating freely, not wobbling, not binding (and possibly, seizing). But people sometimes forget to grease and adjust them – and that can lead to trouble you don’t want, including the possibility of a hub (and the wheel and tire bolted to it) actually snapping off the spindle/steering knuckle due to heat build-up and friction-induced failure … leaving you three-legged at 70 MPH in a curve.
Which is absolutely no fun at all.
Well, how often should bearings be checked? The basic test – checking for excessive drag and “play” – should be done every time the car is up in the air for a tire rotation or brake work. Ideally, once a year. The test is simple. With the wheel/tire off the ground (car on a lift or supported by jack stands) try to spin it by hand. It ought to rotate freely and easily, with just a little bit of drag. If it feels sticky or you can hear grinding noise (really bad) it is very likely that the bearings are in need of grease (minimally) and maybe damaged and in need of replacement.
If it passes the free-roll test, check for excess play (in and out and side to side movement) by grabbing the tire at the 9 and 3 position. Try to pull it toward you and back; a very slight amount of play (check your service manual for the exact specifications for your particular vehicle) is ok. Same for side play. Pull the tire at the 3 – and then the 9 – to check for that.
If it feels a little too loose/wobbly – or you can’t roll it freely by hand/hear grinding noises – you’re going to need to dig into it. The general procedure is straightforward (and for purposes of this story, we’ll be assuming a rear-drive car and working on the front wheel bearings; FWD/AWD cars are bit more complicated but the general process is similar) and well within the abilities of the do-it-yourselfer. You will need the following:
* Floor jack and jacks stands to raise/support the vehicle.
* Lug nut wrench.
* Flat blade screwdriver; socket set.
* A hammer.
* Hi-temperature wheel bearing grease (comes in a tub).
* Parts cleaner/solvent and a small plastic tub/old toothbrush.
* Spare cotter pins.
* Shop manual for your particular vehicle.
The first thing to do is loosen the lug nuts on the wheel you’ll be working on first. Do this before you raise the wheel or it will spin when you try to turn it and you will have a heck of a time getting the nuts loose! Don’t remove them. Just loosen them with the wrench enough that they turn easily.
Now raise/support the car and remove the wheel/tire.
You should be looking at your disc brake rotor/caliper at this point. In the center of the rotor will – ought to be – a dust cap. Underneath this is the outer wheel bearing. It can be greased/checked/replaced without further disassembly. But if the outer bearing is worn (or clearly been running – turning – without adequate grease, probably the inner bearing should be checked, too. Let’s start with the basic adjustment.
Use the screwdriver and hammer to – gently – pry out the dust cap. Set it aside.
There should be a cotter pin and a castle nut facing you. The nut should be slightly less than hand tight. If it’s tighter, it’s probably too tight. To adjust: Remove the cotter pin and loosen the castle nut. Turn it in by hand until snug, then back it out just enough (1/4 turn or so) to line up the holes so you can re-install the cotter pin.
Assuming the bearing (and/or the race it rides in) is not scored – and greased sufficiently – the wheel should now turn freely and there should be no excess play, either in and out or side to side. If so, you’re done. Reinstall the dust cap, using the hammer to tap it back into place, mount the wheel, tighten the lug nuts as tight as they’ll go by hand to seat the wheel. Then lower the wheel/remove the jackstands and tighten the lug nuts (be careful not to overtighten them). It’s best to tighten in a criss-cross pattern, gradually increasing the torque (tightness as you go. Ideally, have a torque wrench on hand and tighten to the specifications listed in the manual. But if unavailable, just a bit more than “hand tight” is usually about right.
If the wheel does not turn freely, if you can hear friction as you rotate the wheel/hub by hand… the bearings (and races) must be physically checked, cleaned and re-greased. If you find any evidence of wear – such as scoring/discoloration (see first pic in this article; note the scratches on the rollers) indicative of excessive heat build-up, or they do not turn freely in your hand after cleaning them thoroughly, they will need to be replaced – along with the races they ride in.
First step is a physical examination, which requires removing them from the hub, which usually requires removing the dic brake rotor – which usually requires unbolting and setting aside the brake caliper. These are typically held in place by two large bolts. Some, as in the case of my old Trans-Am, having Allen (recessed hex) heads – in which case you’ll need to get the appropriate size Allen wrench/socket to loosen/remove them. Support the loose caliper on something or use wire so that it does not just hang by the brake line.
Next, remove the cotter pin and the castle nut. Grab the rotor and pull it toward you. It ought to slide off the spindle/steering knuckle. The outer bearing will pop out (try to catch it so it doesn’t just fall on the dirty garage floor) but the inner bearing will be held in place by the rear grease seal, which is a press fit deal.
Plop the out bearing in the bucket of solvent, then use a screwdriver to remove the inner bearing grease seal. It’s a throw away and can’t be re-used, so buy a new replacement (two of them, if you’ll be working on the left front and the right front hubs). You may also want to preemptively buy new inner/outer bearings (which will include their matching races). Maybe just buy one of each, since you may only need to replace one of each (and be able to re-use one each of your old ones). They’re not expensive, at any rate (mine cost about $10 each). So buying a matched set (four total; two inner, two outer – plus a pair of grease seals) is probably the best bet.
With the grease seal out, the inner bearing comes out easily. Soak it in the tub of solvent. Use brake cleaner spray and old rags to clean the area around the races (they’re press-fit inside the rotor) and examine them for scratches or other obvious indicators of wear. Use the toothbrush/solvent to clean the bearings; you want all the old grease out and all the metal visible for inspection.
If the bearings are bad, the next step is removal of the old races. The easiest way to do this is to dig in your toolbox and find a socket with an outside diameter about the same as that of the bearing you want to get out. Use it – and the hammer – to knock out the old race by placing the socket on the race’s shoulder and tapping on it with the hammer. The outer race comes out toward you, if you’re facing the hub/rotor with the wheel studs pointing at you. Turn the rotor upside down to knock the inner race out. Thoroughly clean/wash down the area afterward with spray brake cleaner. To install the new races, use the socket and hammer to tap them into place, being careful to apply force evenly until they’re completely seated.
With that done, you’re ready to grease the bearings and begin the re-assembly process. Grab a glob of grease with one hand and use the other to work it into the bearings – in between the rollers, especially – until the entire assembly is thoroughly coated. Place the inner bearing in its race and tap the new grease seal into place. Now, you can reinstall the rotor/hub back onto the spindle/steering knuckle. Push it on all the way, then re-install the (also greased) outer bearing and the washer (typically) that goes on top of it. Thread the castle nut by hand until it seats. Rotate the hub to be sure it’s seated and re-check your work. Now, back the castle nut out just enough (about 1/4 turn, as we talked about above) to allow you to slide the cotter pin in the hole. Install the cotter pin, rotate the hub while listening for any sounds that aren’t right – which means any sounds of friction, such as scraping – and excess tightness; the hub/rotor ought to turn easily by hand.
Reinstall the brake caliper. Mount the wheel/tire on the hub.
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