(Car) brake thing...?

Lately I’ve noticed that sometimes (not all the time), near the end of a slowdown turning into a stop, the car feels like it’s “shimmying” a little, as if I were driving down a grooved road (which I’m generally not). The car underwent minor maintenance two months ago, so everything was presumably checked then.

What could this be, and what should I tell a service tech, if I should visit one?

Besides having your brakes looked at, make sure you examine your tires. Letting the wearbars surface will cause a shimmying effect too.

Oh, I wouldn’t expect that the brakes had been looked at if the problem you brought the car in for was unrelated.

“Shimmy” is a technical term, you can just say that.

Oh, then if it’s a technical term, I’m not sure I should use it, since I don’t know what it “technically” means.

What are wearbars? I was told at the maintenance (which was done as a general tune-up thing, and NOT for any specific “problem”) that there was uneven wear, and an alignment was done, but that’s about it as far as the tires go.

It can be a combination of warped rotors in the front and worn ball joints. How many miles on the car?

Rotors are not expensive to replace or have turned.

It only happens under braking? And only at slow speeds? I would be guessing break rotors as the culprit… but it could be lots of things.

I would say brake rotors also. If not fixed, it will eventually cause the ball joints to wear out, too.

56K+ miles, I think.

So looks like the consensus is to take it in and consider any wasted expense payment for peace of mind? I can never tell when this kind of thing is my imagination or not. I’m still second-guessing myself as to whether I missed anything, whether it happens ONLY at slow speeds, etc. My lack of car knowledge is the main barrier here.

Front wheel drive is a major pain in the ass these days. If they’re not wearing out tires “prematurely”, they’re having drive/steering problems.

Oh, the tire companies are rejoicing as are the suppliers of front end parts…

At that mileage it’s probably not a ball joint.

I would guess you’re rotors are slightly warped. Each front wheel has a rotor which is nothing more than a disc shaped piece of metal. On each side of it is a brake pad that grabs the disc. It is operated by a piston on one side. Imagine holding a dinner plate with your fingers. The plate is the rotor and your fingers are the brakes. What happens is that repeated stops heat up the rotor and it warps. When it is warped you feel it while braking because the pads are grabbing the rotor as it turns. It is most noticeable when you are lightly braking. It is not a safety problem. the fix for this is to have them turned. this means removing the rotors and shaving metal off until they are back to specs. This can only be done if there is enough metal to shave off. Otherwise the rotors are replaced.

Just for further info, when talking about rotors they refer to cars with disc brakes. Most cars have at least front disk brakes. The other type of brake is a drum brake which may be on the rear of the car. If your car has anti-lock brakes then you probably have disc brakes on all 4 wheels.

Years ago it was popular for car makers like Honda to put metal brake pads on their cars. this means the brake pads had a lot of metal in the material. It’s great if you’re racing but they tended to warp the rotors quicker.

picture of a disc brake assembly.

When talking to a mechanic just say the car shimmies under light braking and you suspect the rotors need to be checked. They will check the brakes for wear and if they are really worn you should be able to see how much pad is left. Here are pictures of disc brake pads.

You can google “how to change your brake pads” to get a feel for what things look like so you’re comfortable talking with mechanics.

Could also be Tramlining. Most roads do have “ruts” in them.

I have a similar problem but it wasn’t the rotors. The way ABS works on some cars is that there is a little cog-like rotor on the axles. The ABS sensor sees the gaps in the cogs and can work out the speed of that wheel. By comparing the speeds from all 4 wheels it can work out which one is locking up and let pressure off that wheel’s brake. On my car one of the teeth was broken off one of the cogs. The ABS sensor saw this as that wheel locking up so pulsed that brake. This gave the shimmying feel you describe.

A wear bar (or tread wear indicator) is a bump or ridge molded into the groove of the tire tread. When the tread wears down far enough after X,000 miles, the wear bar is even with the top surface of the tread and forms a bridge between neighboring tread blocks; at that point the wear indicator is indicating to you that it’s time to change your tires.

This guy’s finger is pointing to one on a brand new tire. More info here.

Yep, sounds like rotors out of round. The good news is that even if they need to be replaced, they are a pretty cheap part on cars.

Yes, it certainly sounds like warped front rotors. This is easily verified by anyone who has experience with these things. You don’t say what the mileage is on the brakes. Warping can happen at any mileage due to various conditions. New rotors can get warped simply going through a puddle when the brakes are hot. Old rotors often become warped when the calipers begin to become engage mostly on the inner or outer side, which causes extreme heat on that tight side. The calipers also don’t relax as much when that old hardware becomes rusty and worn. I suggest that you have a brake specialist check it out because you most likely need some brake work.
As stated elsewhere, other suspension components need to be looked at too in case there is wear on safety related items.

Brake rotors don’t actually warp. What they do is that they get so hot that some of the pad material actually fuses to the rotor in an uneven fashion, and this causes the brake pedal pulsation you are feeling, as the pad material encounters spots on the rotor with different frictonal properties.

Turning the rotors can alleviate this problem, however in an effort to save weight, most manufacturers are making the rotors thinner so that they cannot be turned once they have been on the car for a while. At 56K miles I would not expect you to be able to turn the rotors at all.


That’s not correct. Brake rotors can and do warp. I’ve seen some on a brake lathe where one can see the cutting tip on one side hitting metal where the tip directly across is touching only air at one spot, while at another spot the latter tip will hit the metal and the former will not. And no, it wasn’t from the rotor being mounted cockeyed to the lathe.

It may well be that many rotors labeled as warped are not, and that rotor runout problems are often caused by factors other than rotor warpage, but it’s not true that rotors cannot and do not warp. They can, and they do.

Sorry, I should have said that most often, what people complain about as warped rotors typically are not. The kind of heat you need to generate warping as well as the kind of mounting problems that contribute to it, are just not that common anymore.

It’s a heck of a lot better than it was 20, 30 years ago. Nowadays you can drive a car for 100,000 miles before having to do anything major. Most cars from the previous generation wouldn’t even last 100,000 miles.

Please remove your head from your buttocks. 20 years ago was 1990. I had several cars of that era all last over 100,000 miles with basic maintenance, and it was not uncommon. One I even turned over 200K. Did they have more problems at 100K than cars do now, sure, but getting to 100K was not an issue for most cars built in 1990, or even 5 years before it.