Steering wheel vibration

Given the recent history, the list of suspects is pretty short. This should have been noticed during the test-drive that was part of the alignment, but regardless, to replace the wheel bearing assembly requires removal and reinstallation of the brake rotor. Given the age and mileage of the vehicle, there was likely rust and scale on it, and a chip might have broken off and became lodged between the hub and rotor or between the rotor and wheel. Either one will cause the wheel to wobble slightly and be felt in the steering wheel.

The place to start is by returning to the shop that did the work and give them a chance to correct any mistakes and to look for the cause of the vibration. The best approach is to run the engine, in gear, on a hoist, and observe if the wheel is wobbling. If there is not enough wobble to be seen, the next step is to use a dial indicator to measure the "lateral run out" at the lip of the wheel in the area where the balancing weights are clipped on. Every wheel has a little run out, but an acceptable amount is probably in the area of 0.030" or less. When you can feel the vibration and see it in the steering wheel, you can expect to find considerably more run out than that.

You also have to consider the speeds at which this occurs. If you only feel it at highway speeds, don't overlook the obvious wheel weight that fell off. Being a mechanic, you know what that feels like.

Also don't overlook a broken tire belt, especially if they were rotated during the previous service. Don't ask me why, but those often show up right after a related service that had nothing to do with the tires. This has happened multiple times on my old Grand Caravan daily drivers. Run 30 miles to my friend's shop to use his hoist, and within a week I have a broken belt. Of course I get the last ounce of life out of everyone elses cast-off tires, so it can be expected, but three times I developed a broken belt within a week of replacing a brake line or repairing an exhaust leak.

If lateral run out is not excessive, switch the wheels / tires front-to-rear and see if the vibration feels different. If it does, especially if you feel the back of the car wobbling back and forth, there is a more elusive type of broken tire belt to look for. We're all familiar with the hump, or tumor, that causes a bulge in the tread surface, or in extreme cases, an "S"-shaped wobble in the tread, but a more subtle break can cause the same sensation. The break occurs over such a long period of time, the tread surface has time to wear smooth so you don't see any bulge. Instead, you have to look at the carcass of the tread at the deepest part of the grooves between the blocks of rubber and watch if that surface rides up and down as the tire is rotated. This type of defect is easier to see when running the engine, in gear, on a hoist, so you can stand still. When spinning the wheel by hand, your body movement can make this type of tire failure difficult to see. You can also find it by spinning the assembly on a tire balancer with the power turned off. You'll see the wear indicator bars as they pass by, but those are real small. The broken belt will look similar, but will be much longer / more noticeable.

The hump from common broken belts pushes the car up each time it comes around and hits the road. This can knock your teeth out at higher speeds. The second type of broken belt is unable to support the vehicle's weight, so each time that area comes in contact with the road surface, the axle drops down a little. You'll see this best at real low speeds, like when driving through a parking lot. The steering wheel will oscillate back and forth a little. At highway speeds, that weak area is there and gone so fast, the axle doesn't have time to settle to a lower position, so you are likely to not feel it.

The last, and least likely suspect, especially at the relatively low mileage you listed, is wear inside an inner CV joint housing. Before this gets real bad, it shows up right after some other service that resulted in the engine sitting slightly left or right of where it was. That includes replacing an engine mount that sets that position, or removing the engine cross member and reinstalling it without marking its orientation first. GMs are one of the few brands where you can do this as the mounting holes are a lot larger than the bolts that go through them. Anything that moves the engine, even as little as 1/16", causes the three rollers to run in a different area inside the CV joint's housing. With that wear, the rollers run in and out of that area, and when the engine is under load, the rollers bind and don't want to roll smoothly. Most commonly this causes a hard steering wheel oscillation up to about 35 mph, typically when turning and accelerating, as in when turning from a parking lot and accelerating down the road. The binding rollers cause the half shaft to push and pull on the wheel bearing and spindle, and that tugs on the steering linkage. When bad enough, it also shakes the engine left and right. The biggest clue here is the vibration completely clears up when cruising at a steady speed.

Check out this article too for more information and ideas of things to look for:

https://www.2carpros.com/articles/steering-wheel-shakes-when-accelerating-or-braking

Please let me know what you find and if we need to look further.

My first reaction is that doesn't make sense, but I'll withhold my skepticism until I hear back from you. While working at a very nice family-owned dealership through the '90s as their only suspension and alignment specialist, we had a common problem with Goodyear tires that caused a noticeable pull to the right. Replacing the tires would solve the problem, but there was actually nothing wrong with them. Due to the high cost, the manufacturer didn't want to replace them under warranty, and in fact tire warranty is always handled by the tire manufacturer through their local dealer. They too wanted to avoid the cost of replacing thousands of tires that really were not defective. The manufacturer's service bulletin that addressed this problem called for readjusting the alignment to create a hard left-hand pull to offset the exaggerated right-hand pull caused by the tires. Having test-driven hundreds of cars after aligning them, I could tell the cars didn't seem to handle quite right, but they did indeed go straight when you let go of the steering wheel.

All of the car owners were satisfied after the alignment change, but I always explained what I had done and why. If I kept quiet, the first time they had to buy new tires, those would not have that characteristic pull to the right, and with the hard pull to the left I had adjusted in, those customers would complain that their new tires were causing a left-hand pull. If the tire store offered to check the alignment and found the hard left-hand pull I had adjusted in, the customer would likely not believe them. In their mind, someone is lying or is covering up a problem.

By simply explaining their car would need to have a normal maintenance alignment when they bought their next set of tires, all that frustration could be avoided.

The point of that story is weird things can happen with tires. Flat spots are caused by sitting on the tires for a long time, as in weeks or months, or by skidding for a long distance without that wheel rotating. Skidding flat spots are caused by part of the tread being worn away. The vibration caused by that takes a real long time to go away, if it ever does. Flat-spotting from sitting a long time goes away within a few miles as the sidewalls flex repeatedly. That was a real big problem in the early years of radial tires, but we don't hear about that any more.

As for the tire pressures, I never went by the door stickers because the pressures listed there have to take into account any replacement tire you could buy. In the case of the vehicles I was aligning, some had maximum pressures, as listed on the sidewalls, of 35 psi or 44 psi, but there were some replacement tires from a local farm and home store with maximum pressure of 32 psi. I found tires listed at 35 psi max rode best when inflated to 35 psi, and those rated at 44 psi max were most comfortable at 40 psi. By using those two pressures, I never had a single complaint of harsh ride

We all remember Ford's many lawsuits over under-inflated tires. They put 28 psi on their door stickers to make their vehicles ride more comfortably than those of their competitors, but those tires should have been running at 40 psi. The problem is, if a manufacturer puts "40 psi" on their door stickers, that only applies to the tires that came new on that vehicle. If you buy a set of tires rated at 32 psi max, then go by the door sticker and inflate them to 40 psi, they will be badly over-inflated and risk a blowout. That's why the stickers have to consider all the tires on the market, not what is best for the specific tires on your car.

Most tires today are rated at 44 psi max, so running yours at 40 psi for a while won't hurt anything, but my skepticism comes from the fact if flat-spots really are causing the vibration, that should have gone away long before you went back to the shop. Please keep me updated on this and on what the final solution is.