Coincidental mechanical failure?

July 15, 2009 8:24 AM

MeChanics, a moment, please! Could wheel bearing failure be caused by improperly replacing brakes/rotors on my car?

Hi guys! I've got a 2002 Ford Focus ZX3 with about 90,000 miles on it. I have done my best to lovingly maintain it over the years and have generally had no serious issues with it.

One thing that I have dealt with is a wheel bearing going bad, though--After googling a bit, I have taken notice that the Focus wheel bearings are a bit prone to failure (and frequent failure, at that, apparently...).

In any case, I believe that I am currently experiencing another wheel bearing failure, as there is an ever-present drone at speeds higher than 30 miles per hour. While it is fun to imagine that I am piloting a B-17 on a WWII bombing run, I would like to have my friendly neighborhood repair shop address this. But herein lies my question, as I wonder if they might have caused the problem and would at least be willing to lop off a bit of the repair cost:


Each time I have had a wheel bearing go bad, it has happened within a week of having new brake pads and/or rotors installed. Is there some part of the brake replacement procedure that could cause the wheel bearing failure? Perhaps something that is being overtightened or somesuch?


In case this is a possibility, I would also note that the current problem seems to be coming from a front wheel (disc), and the failure I had repaired a few years ago occurred with the rear wheel (drum on the ZX3).

What do you say, friends? Is this just a coincidence, or a case of something being inadvertently overtightened..?

posted by Jinkeez to travel & transportation (9 comments total)

I vote for the bearing failure being coincidental to the brake work although due the proximity of the two systems, I can't completely rule out that the two are related. Sorry that that is no great help but I think that only a mechanic who has actual experience with that car could give you a more distinct and valuable answer.
posted by bz at 8:28 AM on July 15

It could be somewhat caused by the brake job, but not in the way you think: in the loosening and re-tightening of bolts and whatnot during the brake job (tightening to spec, of course), things might have set up to make for a wheel bearing failure.

Which is to say, even if it is no-coincidental that the wheel bearing shit the bed after a brake job, the wheel bearing *should* be able to take that small amount of abuse. So it's still on the wheel bearing design, not the shop's.
posted by notsnot at 8:36 AM on July 15

Two things:

1- Are you sure it's not a tire issue? Before paying for a bearing, have the tires rotated. Depending on how the tire goes funny, it can sound almost the same.

1b- Or, in the process of doing a brake job, the tires were rotated and the different wear patterns of the new tire just made an already failing bearing sound worse.

2- If the brakes failed because they are dragging, this will cause the whole hub assembly to heat up and cause premature failure of the bearing.

3- If you have alloy wheels (instead of steel wheels with a hubcap), those can tend to get stuck on. Something to do with the tightness of the clearances, and a reaction between the two metals. If this has happened, a ham-fisted mechanic will just whack on the wheel until it comes off. This can be damaging to the bearing.

4- This happened to me on a Ford of similar vintage. I was doing a brake job, and the brake rotor was just plain stuck on (similar to above). I had to cut it off. But if that happened to your car, and the mechanic was similarly a brute-force kind of person, he would beat on the rotor with a sledgehammer until it came off. This for sure will damage the bearings. They just aren't made to handle that kind of force- they are designed to go at high speeds for a hundred thousand miles, and hit quite a few bumps along the way. But those bumps are moderated by the (relatively) squishy tire. A good whack with a sledge hammer is more force than it can take and will wreck it in short order.

In other words, if your mechanic is doing a good job, it's a coincidence. If he's not, it still could be a coincidence. But it is *possible* that it's not.
posted by gjc at 8:49 AM on July 15

Generally, wheel bearing failures would be coincidental to brake work, but...

If you had a bearing that was already going bad, some extra heat making its way into the hub/bearing area from new brake parts dragging a bit (especially if you didn't have the front disc calipers replaced or rebuilt when the pads were replaced), could cause the outer bearing race to expand just enough that you soon heard the noise of the nearly bad bearing.

Some mechanics still make pulling hubs and inspecting and repacking bearings part of a comprehensive brake job, just as they generally replace all brake hardware and recommend that calipers and brake cylinders be replaced or overhauled, and brake fluid (which will degrade due to pulling water vapor out of the air, over time) be fully flushed. Those kind of "brake jobs" will not be the cheapest, but will insure that the car doesn't come back soon after for related problems.

But in these days of consumers looking for the absolute lowest cost/quickest/least parts work they can get, a lot of mechanics have either started quoting the bare minimum wear parts replacement and labor, or gone to a Bronze/Silver/Gold "package" approach in selling services. To some extent, you do get what you pay for in automotive maintenance services. So long as you understand what you're getting, and are sure it matches your driving style and vehicle wear patterns, that's OK. But, personally, I want the bearings inspected and repacked at every brake inspection interval on my vehicles.
posted by paulsc at 8:52 AM on July 15

in auto shop class we were taught that a bearing inspection/repack is a critical part of a brake job. it's one of those things that just makes sense, since you should be having your rotors machined anyway (which implies having the disk removed and the bearings exposed). seconding paulsc.
posted by klanawa at 9:12 AM on July 15

If your bearings are already crummy and your rotors are seized onto the hub with corrosion, the standard procedure of striking the old rotors with a hammer to shock them free of the hub might exacerbate your bad bearings. Your location, up North in NY, is EXTREMELY prone to corrosion and some heavy-duty smacking could be required to dislodge the old rotors. Lots of corrosion builds up between the inner face of the rotor flange and the face of the wheel hub. They can be on there pretty tight.

On many new vehicles, wheel bearings are sealed units that cannot be repacked or inspected. On OLD CARS, the wheel bearing will fit onto the spindle and the hub or rotor will contain a race that helps hold the bearing together. That hasn't been the case for a while. Every late model car that I can think of (since 2000) has a sealed bearing unit that's pressed into the spindle with the hub pressed into the center of the bearing. They don't get repacked, because I'd have to essentially demolish the old unit with a 20 ton press to get it apart. At that point, I'd just install a new bearing because the old one would have spilled its guts all over the floor around my press.
I've replaced brakes on a few Ford Focuses (Foci?) and there's no way of inspecting the wheel bearing, even with the rotor removed.

Also, machining rotors is really old news, too. It's cheaper just to install new ones, rather than REMOVE MATERIAL (so silly) from a piece of metal that is exposed to huge amounts of heat. Cutting late model rotors is a great way to heat-warp them before their next brake job. New rotors are a cheaper, lighter, less durable alloy than the rotors of Olde that were substantial enough to cut. The most recent vehicle that I can think of that has a wheel bearing integrated into a rotor is a late 90s VW/Audi Passat or A4, on the rear disks. And even that requires pressing the old races out of the rotor to install in the new rotors.

Overtightening won't damage your wheel bearing as much as it could warp a brake disk slightly.
posted by Jon-o at 9:43 AM on July 15

I agree with Jon-o. Perhaps, also, if the brakes were bedded in properly, the extra heat may have had some effect. But the wheels undergo a tremendous amount of shock while driving---those rotors would have to be really stuck.

There's nothing that could be over-tightened. Warp the rotor, yes; bearings, no.
posted by luckypozzo at 11:45 AM on July 15

Thanks very much for the answers, everyone, I really appreciate it! Will have my shop check out the noise and verify it is indeed bearings making the noise, have them fix it, and chalk it up to bad luck and coincidence. :)
posted by Jinkeez at 12:40 PM on July 15

Most newer cars don't have bearings that can be repacked. They are sealed units that are greased for life, and generally last a good long time.
posted by gjc at 5:59 PM on July 15