When braking I notice a low whine (sounds like blowing air across the top of a soda bottle) from the front. Pads and rotors replaced last summer and there does not appear to be any obvious abnormal wear. Rotors appear smooth. The whine happens after the car has been driven more than a few miles. I don't notice it the first 1 or 2 miles.

Is this an indication that the front bearings need repacking? This car is a 1992 300E with 175,000 miles.

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ARVY

1999 E430
1999 C230 Kompressor
1992 300E (write-off)
1984 190D 2.2 (sold)

It could be a failing bearing. If the noise is indeed from the bearing, it's too late to simply regrease it. You should be able to see damage to the surfaces (races and tapered rollers) if it's the culprit.

Don't wait for it to lock up and ruin your spindle.

I agree with MattL that if the inner and/or outer wheel bearing(s) are worn beyond normal tolerances they need to be replaced. Though do check to see if they were torqued properly if the rotor was removed when replacing the calipers. In my opinion, since it takes a few miles for the sound to appear (or at least to become noticeable) it doesn't sound like a wheel bearing issue. In addition to the possible bearing wear Matt referred to, take some of the wheel bearing grease between thumb & forefinger and slide them back and forth to see if there is any detectable grit, which might be metal shavings from bearing (though if it is wheel bearing wear, the particles may be well too small to feel). It almost sounds a vacuum brake boost problem rather than a wheel bearing problem, which you could check with the help of a friend. Check for vacuum leak both at the booster and the vacuum source, as well as the vacuum hose itself. 192k doesn't sound like enough miles for front wheel bearings to fail unless they've been exposed to excessive water that got by the inner seal or the dust cap, are not torqued improperly, someone used grease not designed for wheel bearings; in general, have suffered abuse. The vacuum brake booster, if it is leaking vacuum, is easy and free to check, so personally I would check that out; the rubber bladder in the booster could also be the source of the problem. All of these rubber-based elements of the vacuum boost potentially could be non-symptomatic until they begin to heat from heat radiated from the engine. Let us know what it turns out to be.
(Edit) Generally, wheel bearing failure tends to produce sounds that might be a whine or a low-frequency rumble and should cause some steering/handling problems. A vacuum leak is more likely to sound like the gentle flowing of air across the neck of a soda bottle (a very distinct whistling, versus a whining sound).

I had a front wheel bearing noise that sounded like a howling tire. It turned out to be a tiny nick in the outer bearing race. So I replaced all my German-made bearings with ones that are stamped Mexico. Not sure if they will go for 200K like the first ones did, but the car sounds a lot better now.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

Arvy said he only gets the noise while braking. I doubt a bad wheel bearing can do that. I'd look into the pads and whether anti-squeal paste has been properly applied.

Ray, it's unfortunate your first bearing had a nick in it. Any bearing with a nick in it will produce noise. In general, I still recommend German-made bearings over Mexican-made bearings anytime.

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95 E320 Cabriolet, 169K

Thanks for all your replies.

To KESTAS: I replaced the pads & rotors last summer and did apply that anti-squeal stuff. Pads & rotors were all MB.

To RALPH: I will look into the vacuum brake boost as a problem. Took the car to my indy and was able to replicate the problem for him. Now he knows what it sounds like and doubts its the bearings. Should I have him repack the grease in the bearings since he'll be working in that area anyway?

When I drove the car to the indy to try and replicate the sound. I can confirm that the sound only occurs when the car is driven at slow speeds stopping / braking frequently like in a traffic jam. If the car is driven at hwy speeds (above 40 mph) and I brake hard, it stops smoothly and sounds normal (ABS also comes on normally). Sound only occurs in slow traffic / frequent braking conditions.

I hope to have this resolved soon and will post an update.

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ARVY

1999 E430
1999 C230 Kompressor
1992 300E (write-off)
1984 190D 2.2 (sold)

If it helps any, the brakes on my car (Pagid) also have low speed squeal and groan, even though the calipers were properly cleaned and lubricated, and antisqueal paste was properly applied during the last brake job. I believe this is the nature of the brake pad compound and the rotor material. I'm simply resolved that this is the nature of the high-performance system.

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95 E320 Cabriolet, 169K

I don't know how I missed the "while braking" part up there. Oh well.

it may also be worthwhile to check for loosness in the bearings. to do this you should lift the car high enough to get the wheel off the ground, then grab the wheel and try to wiggle back and forth. a bearing will work loose sometimes, normally at about 80k or so and can at about any time after that. a little mechaincal sounding and feeling loosness is the symptom. it is one of the first things i check when i buy a new used benz.

my son in law had a 85 944 turbo porsche, and told me that the mechanic said he needed ball joints for about 1000 dollars. we checked the wheel bearings and a half hour later the loosness was gone.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

An update...my indy could not find anything wrong. He did change one inner bearing and repacked and sealed the front bearings. Brakes check okay. I'll keep an eye out for it but will not worry myself. Thanks for your replies!

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ARVY

1999 E430
1999 C230 Kompressor
1992 300E (write-off)
1984 190D 2.2 (sold)