Hot lug nuts, no always, caliper or bearing?

After feeling and hearing a vibration of sorts while driving on the highway with my 2010 Sonata, I arrived home about 10 minutes later. The vibration came on sudden and then subsided. At first I thought it was the road surface, but that wasn’t it I thought later.
At home I felt around, and one of the wheels had very hot lug nuts, too hot to touch. But the wheel I didn’t find very hot. The other lug nuts on the other wheels were cool.
I took the car into my mechanic and all he thought was needed was a brake service. He took all sides apart and got everything to move smoothly.
I then drove about 30 minutes on a country road without much braking action, and stopped to check the nuts. Again, same wheel, hot nuts. Other wheels, cool.
Given the heat is more in the center and not so much the whole rim (cheap steel rims), and given the vibration before, I thought maybe the bearing is bad.
Before returning home (I canceled my trip 30 minutes in, because of the heating problem not being solved), I let it cool down for 15 minutes give or take.
I then drove back home. To my surprise when I got back home, the nuts were not hot. Same cool feel as the other wheels. What gives? It’s an intermittent problem?
First opinion is probably caliper not retracting properly, and to replace it.
But could it still be the bearing? Is it possible that a bearing shows an intermittent problem?
Another small detail: that last trip (today) where I canceled it after 30 minutes into it, I though maybe there was that vibration again - but only very slightly, and it is easy to confuse perhaps with the exhaust. There are no exhaust issues. It’s hard to describe the vibration. It’s subtle now.
That trip home, I felt that there was no vibration at all.
So maybe that subtle vibration coincides with that overheating. When I heard that vibration, I thought that pressing the brake pedal a few times did not make it go away.
Does anyone have any ideas? Could a stuck or not properly moving caliper cause a vibration? Perhaps making the pads jump back and forth enough to make that vibration? Again, this vibration is very very subtle now. It was pronounced for about 3 minutes on the highway when it first occurred, but subsided after about 3 minutes.
It would be logical that if it were the bearing that you always get the same result, where 30 minutes of driving would always make it hot, and not just once in a while, right?

Jack up the wheel and spin it by hand. Listen and feel for noise, maybe wheel bearings or rubbing rotor against calipers.

Do you think that the bearings can be bad in such a way where it does not always heat up? On one 30 min drive, the lug nuts were hot, and on another 30 min drive the nuts stayed cool.

My gut feeling says no, it is not the bearings but rather something with the brakes. I can see a sticking caliper intermittently working, but not a bearing.

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Yes. Probably either a sticking caliper piston or bad rubber brake hose to that caliper.

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Quite likely the problem.

Not very likely. Bearing problems are not intermittent and they are nearly always noisy - a growl that changes pitch with speed

Another likely possibility; a failing rubber brake hose on that corner. It acts like a check valve and holds pressure on the caliper acting like a stuck caliper. If you can create the problem and then reach under and crack open the bleed screw, watch for a squirt of fluid and them drive away with no drag, it’s the hose, not a sticking caliper. If the bleed screw doesn’t squirt, it’s more likely the caliper.

I don’t recall ever seeing a failed wheel bearing causing the hub/rotor to get hot. When a wheel bearing wears enough to get hot it quickly becomes too loose to drive.

It sounds like you are pretty much on top of the diagnosis there OP. I’m thinking you may have some kind of ABS problem happening there. That could explain the pulsing/vibrating sensation and that only one wheel is getting hot. Have your shop check for unequal tire pressures, or for a faulty wheel speed sensor. I may be possible to temporarily disable the ABS system. If so, might be worth a try.

The mechanic got back to me after looking at this. He thinks it is the parking brake cable. Something about one side having to be fixed, which also means that the other side should be fixed. Cable + 2 x something for both sides + something else? 3 hours of labor. $600 CDN…

for $600 he better be sure. Btw, for some reasons I assumed it was the front that’s been giving you trouble.

So it is a rear brake. (?) Do you routinely apply the parking brake?

Jack up each rear wheel and spin it…does one drag more than the other? If no, drive without using the parking brake for a while…do the lug nuts ever get warm?

I always use the parking brake. It’s too late now. The car is staying overnight at the shop. Parts arrive tomorrow morning. I didn’t know what else to do. That’s the frustrating thing with mechanics, feeling forced to trust them and go along with whatever they say. What consumer actually understand their own car…

It’s a normal recommendation here that whenever something is done to the brakes on one side of an axle, the same should be done on the other side.

There’s a customer interest bulletin on the parking brakes on some of these vehicles, might want to see if it applies to your car Can 3-5-2/1.13.2003.

I’d have guess it would be about $150 in parts and 2 hours labor. It may be there’s more than just the parking brake cables involved.

There’s plenty of information available. The owner can purchase an aftermarket repair manual, like Haynes or Chiltons, inexpensive. For more $$ the factory service manual provides all the information the dealership shop has access to. Some manufactures allow owners to use their computerized repair information for free or a small fee. It’s available over the internet. And if that’s not possible, the owner can purchase a one-car subscription to the AllData internet repair database for a small fee. That’s sort of an abridged factory service manual. That’s what many inde shops use as their repair information source. Some public libraries have that too.

To understand what the repair manuals say however takes some study time. A lot of unfamiliar terms used, and they assume the reader is familiar w/basic car repair procedures, which most owners aren’t. And most owners just want to drive the car and let the shop repair it. Nothing wrong w/that model either. Owners are welcome to ask questions here when they come up of course too. Best of luck.

It was Hyundai and Kia that allowed you free access to their factory technical website. But that ended a few years ago, as they finally realized that the information is valuable. This was around the same time, that their cars started becoming very good, not disposable garbage

I doubt withdrawing that benefit hurts car sales much. Most owners are not interested in the details of how the car works or how to repair it.

You’re the only one mentioning car sales. I sure didn’t, nor was I even thinking of that

I’d guess the reason they offered that ownership benefit was to improve customer satisfaction, yielding future sales. But I could be wrong, maybe they had another reason to do that. Were they just being helpful?

I don’t think it had anything to do with customers

I believe it was so that independent shops and fleets would have an easy time working on their vehicles. Until they realized that information is a commodity, one that can be sold for a handsome price

Probably most of the guys that logged on for free were mechanics and independent repair shop owners, not the actual Kia/Hyundai owners

Ok, I see what you mean. It was never intended to be a customer benefit. Just worked out that way for a while is all for customers in the know. Makes sense.

The way I heard about it in the first place was in one of the online trade magazines for mechanics. One of the writers had mentioned it, and the fact that it was free

Well, it was nice while it lasted