What causes a high pitched intermittent squeal while driving?

[Mark R]

My vehicle is a Lexus IS250 with almost 140k miles.

I'm getting an intermittent squealing from one of the wheels while driving. It's very high pitched, not a rumble, and intermittent: it comes and goes, chirping several times a second, occasionally lasting for a couple of seconds. It's related to road speed, not engine speed, and it's coming from one side of the car, so I'm pretty sure it's a wheel.

I can't detect it under hard acceleration, but this may be due to engine noise. It happens during light acceleration, cruising and overrun coasting. But, it seems to stop during braking.

Pads and rotors look OK. No obvious scoring or heat damage.

Rear brakes had new rotors, pads and calipers about 5k ago. Fronts are older.

I'm guessing this is a brake problem, rather than a wheel bearing problem. Any idea what the prob might be?

 

[AMCRambler]

Scared wife in the passenger seat?

 

[AMCRambler]

More likely brake pads vibrating. They have stuff you can spray on the back to dampen vibration. It works for a while but eventually water washes it away and you have to reapply. Could take the pads off and make sure there's a sheet metal shim over the backing. Most pads come wih this but the cheap ones sometimes don't.

 

[FuzzyDunlop]

Scared wife in the passenger seat?

Or the hooker in the trunk?

 

[boomerang]

Take the front wheels off and take a closer look at the pads. I'm betting one or both inboard pads are worn to the wear indicator. Goes away when braking is the giveaway.

 

[Meghan54]

Take the front wheels off and take a closer look at the pads. I'm betting one or both inboard pads are worn to the wear indicator. Goes away when braking is the giveaway.

^ This.

 

[redyouch]

It's either the brake pads or hub bearings. Most likely the brake pads--when were they last replaced?

 

[Mark R]

Sound seems to have gone for the moment.

I inspected the front pads. There's about 3/16" of friction material left on the front pads, which I would have thought would be OK.

But I don't really know how much material is meant to be on these pads.

 

[ino uno soweno]

Passenger side, Tie rod end or rack, ?? .

Just a suggestion. ??,

 

[T2urtle]

i know you said it goes with road noise....

But what about a serp belt. Kinda a long shot but i dont think it a bad shot.

 

[jaha2000]

Sound like the wear squealers on the pads to me.

 

[Vetterin]

Sound seems to have gone for the moment.

I inspected the front pads. There's about 3/16" of friction material left on the front pads, which I would have thought would be OK.

But I don't really know how much material is meant to be on these pads.

Do BOTH the outer AND inner pad have 3/16"? Usually the inner will wear out sooner but either way 3/16" should be close to the wear indicator level. New pads are about 11mm (7/16").

 

[Mark R]

Do BOTH the outer AND inner pad have 3/16"? Usually the inner will wear out sooner but either way 3/16" should be close to the wear indicator level. New pads are about 11mm (7/16").

Yes. The wheel has come off, and both pads are somewhere between 6 and 7 mm.

The disc is worn very asymmetrically though. There is a small lip just under 1mm on the outer surface, but a bigger lip, almost 1.5 mm on the inner surface.

Could this be caliper binding (something that this model is notorious for, and which my particular car has had 5 new calipers [previous owner] for over the course of its life).

 

[phucheneh]

Five new calipers?

...it didn't need one one those. 99% of the time, if the caliper is not leaking fluid past the piston seal, it is fine. Remove slide pins, clean and lubricate, profit. Clean or replace (hardware kits are cheap, but aftermarket ones frequently suck) the pad slides at every brake job.

It sounds like you either typical vibration-based 'squeal.' Lube prevents squealing. Lube is your friend.

In addition to making sure the pins are greased, you want something on the back of the pads where they touch the caliper, and just a wee bit on the pad slides. A little dab of grease can go an awful long way to preventing noise.

If you truly have a 1-1.5mm lip on your rotors, that's pretty major; but it's not a sign of much except not replacing/resurfacing rotors when the pads were changed.

1mm is just under .040". That's enormous. When you turn rotors, you remove maybe .005-.010" a side, tops, depending on the situation. If you had a .040" lip and didn't carefully knock it down with a few passes by hand, the lathe would lock up when the bits hit that.

 

[Mark R]

Five new calipers?

...it didn't need one one those. 99% of the time, if the caliper is not leaking fluid past the piston seal, it is fine. Remove slide pins, clean and lubricate, profit. Clean or replace (hardware kits are cheap, but aftermarket ones frequently suck) the pad slides at every brake job.

Either seized slide pins or seized pad slides. Replacement slides/overhaul kits are not available on this vehicle. Neither OEM, nor aftermarket. I've looked!

That said, it had 100% dealer service, so I wouldn't expect a dealer to suggest anything other than replacement.

If you truly have a 1-1.5mm lip on your rotors, that's pretty major; but it's not a sign of much except not replacing/resurfacing rotors when the pads were changed.

1mm is just under .040". That's enormous. When you turn rotors, you remove maybe .005-.010" a side, tops, depending on the situation. If you had a .040" lip and didn't carefully knock it down with a few passes by hand, the lathe would lock up when the bits hit that.

Rotors aren't reusable on this model, so it's had new rotors every time. The specified pad material is extremely aggressive, and a single set of pads will wear the disc to well below the re-use limit. These rotors only have a 2mm wear limit, so I reckon I'm already below replacement threshold, and I haven't even finished this set of pads.

Thx for the advice. I think I'll just put up with the squealing as it seems likely that it's just vibration related, as the pads/rotors don't have much more life in them. I also reckon I'm going to have to get into the habit of disassembling, cleaning and relubing the calipers every 6 months.

 

[marvdmartian]

Or the hooker in the trunk?

Hell, the person in the passenger seat, when my niece is driving!
(not due to her lack of skills, but more due to her lack of give a shit about the speed limit).