The way to check them is to run the engine, in gear, on a hoist, then listen next to them with a stethoscope. One will sound a little noisy, but the really noisy one will be obvious. The advantage with this bolt-on style is if you replace the wrong one, you can put it on the other side.
Another method is to raise the car off the ground and support it by the frame so the suspension is hanging down. Reach over the tire and wrap your fingertips around the coil spring. Spin the tire slowly, by hand, and if this one is the noisy bearing, you'll feel the roughness in the spring.
One thing that fools a lot of people, including mechanics, is the noise can sound like it's coming from the left wheel, it gets louder when turning slightly to the right, and more weight transfers onto it, and it turns out to be the right bearing that's bad. The noise can be transmitted from one side to the other. Turning slightly, as in when changing lanes, makes the bad bearing get real quiet when you turn toward it because that transfers weight off that bearing. This mainly applies to the lower-cost pressed-in bearings used on Toyotas, Hondas, and '80s Chrysler products. This trick for finding clues usually doesn't apply to the bolt-on bearings used by GM and newer Chrysler products.
There's two things to consider when two new front bearings don't solve the noise. The first is a lot of do-it-yourselfers damage the new bearings from improper installation procedures. In particular, there must never be any vehicle weight on the bearing when the axle nut is not tightened to specs. I had one GM car that had the engine and transmission removed so the people in the body shop could repair the crash damage. When they found out it would take a week to get the parts from the dealer, they pushed the car outside, minus all that drive train weight. That was enough to destroy both bearings. Once I aligned it and took it on a test drive, it was obvious the noise was much louder than any customer could have withstood.
The lowest torque spec I've ever tun into is 180 foot-pounds for that axle nut, and a lot of GM cars call for as much as 240 foot-pounds. That must be set with a click-type torque wrench. A lot of do-it-yourselfers will set the tire on the ground to hold the axle shaft from spinning so they can tighten the nut, but by that time it's too late. It's real easy to just drop a punch through the cooling fins in the brake rotor to hold it.
If nothing pans out by this point, here's something you might consider. There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.
There's multiple versions of Chassis Ear now. The older one used six wired microphones, so you had to drape wires into the passenger compartment. The newer one uses two of those, and four wireless microphones, and another version has six wireless microphones. The original version sold for $200.00 from the guys who drive the tool trucks and visit each shop once a week. You can find them for much less on Amazon.
For my last comment of value, GM builds their ABS wheel speed sensors into the front wheel bearings. These develop real wimpy signals to start with, then, it is normal for the bearings to develop a small amount of play, but that is enough to let the sensor move away from the tone ring to the point the signal drops out. This causes false activation when it isn't needed, mostly at slower speeds because the computer thinks that wheel stopped rotating. The fix for that is another new wheel bearing. This can happen to the new bearing in as little as 15,000 miles. But, ... If your car does not have anti-lock brakes, it uses the same bearing but without the speed sensor. The dealer's scrap metal bins are overflowing with these bearings for the sensor problem. Those bearings will work fine on a car without anti-lock brakes, as long as the previous car was raised up before the axle nut was removed.
If you buy a new bearing for a car that doesn't have ABS, check the prices with and without the sensor. It is real common to find the bearing with the sensor is a lot less expensive than the same one without the sensor. It will work just fine. You just don't connect the wheel speed sensor to anything.
Friday, January 26th, 2018 AT 8:19 PM
