I am getting a low speed rotational noise from the front of my 93 400e that goes away when I step on the brakes.

I have decided to replace the front wheel bearings since the problem is probably either the bearings or a sticky brake caliper.

I've never replaced wheel bearings before, and any input would be greatly appreciated.

Jack
93 400e

Well Jack, I gotta wonder why you made the quantum leap to the wheel bearings. The W124's are famous for a life time of service from the fronts. Bearing noise (front) is not generally heard at low speed, unless the bearings are totally shot. It will get noisy as you approach 50-60 or so if you have a bearing problem. I would redirect to the issue you raise with brake application cancelling the racket. Start there. BTW is it from both sides or just one side? :confused:

jeffsr, I disagree with your characterization of my conclusion as a "quantum leap" since that implies unsubstantiated guesswork instead of analysis.

My line of reasoning as to the most probable factors goes like this:

Either:
(a) the brake pads are dragging on the rotor, or
(b) the hub is moving and dragging the rotor on the pads.

Therefore:
(a) the calipers are not retracting fully, or
(b) the wheel bearings are degraded or out of adjustment.

In conclusion:
(a) the calipers need rebuilding or replacing, or
(b) the wheel bearings need tightening or replacement.

Research resources included:
(a) CD-ROM and paper service manuals for the 124
(b) internet i.e. http://autos.yahoo.com/repair/tree/0.5.html
(c) my brother, import mechanic and foreign car dealer
(d) Mercedes mailing lists and archives

Now, since I have never done this, I could have missed something, so any input will be greatly appreicated.

Jack
93 400e, 92k

jeffsr,

I have also found in my research that older 124s use a brown grease in the front that was superceded by a superior green grease.

You might want to research this, since apparently the green grease does lead to lifetime wheel bearing service, while the brown has a shorter (90-100k) lifespan.

fyi,

jack
93 400e, 92k

Jack, no offense intended, but most of the time with the W124's the wheel bearings are the last source of noise. I have an 89 300E that now has 179,000 on it and I have checked the bearings twice and found that they have never needed an adjustment. If you look at those bearings, they are really "robust" as to size. In my experience (MBZ, BMW and too many Detroit Irons to mention), front wheel bearing noise gets worse as speed increases. Also ramps up when turning, especially at moderate speed. In your thorough analysis you did not mention distorted rotors. The fact that it goes away with braking points away from bearings and points to brake system. I am just trying to point you in the right direction based on 30+ years of building, repairing and the like. You asked for advice. Maybe Donnie or Steve can jump in with something better. Good luck..

jeffsr,

sorry, I just re-read my post, it looks a little stiff. I was not offended, I just realized that I was a little negligent in my reasons of why I thought it was wheel bearings. I see your point, without knowing that I had brakes done it does look like I am out in left field.

I just had the front brakes done three months ago, new rotors and pads. I doubt if it is those, but who knows. And lordy those people are not shy about asking for money for those fancy high-performance brake parts.

Since the brakes are new, it is probably something more exotic, like calipers, god forbid, or wheel bearings.

Who knows, might be distended pads from an oil leak. I am such a novice at this part that I probably shouldn't be guessing.

Thanks for the input.

This conversation reminds me of why I stopped telling mechanics what I thought was wrong with my car when I took it to them.

;)

Jack
93 400e 92k

Jack, can you be a little more specific about the character of the noise, ie scraping, humming, metallic or whatever. New pads, rotors does not always mean a good fix. What was the original problem and did the replacement of those components resolve it. If you had a dragging caliper, then it is likely that you would be able to smell it when you got out of the car. Could be something as simple as binder resin building up on the face of the pads. Was all of the replacement stuff OEM?? It has been my experience that if a bearing is shot or on the way to being shot, use of the brakes has very little effect on the level of the noise. In fact on a BMW 325 that I owned, use of the brakes made the bad bearing even noiser..

jeffsr,

noise is like this "rum rum rum rum rummmmmmmm rum rum " and then when I hit the brakes "ruummmmp!" and away the sound goes, going up in tone and disappearing. Sometimes comes back right away, sometimes not.

I do not know for certain if the stuff was oem, but the shop I take it to is very reputable and the trust factor is high with these guys. I have not laid eyes on their brake work.

I intended to look at the brakes for buildup/contamination when I had them off.

I agree, probably not the bearings, but another thing I found out in my research is that the brake carrrier bolts have microglue on them (overengineered, like it) and should be replaced every time you take them out. And I figured, while I am in there, I will check the grease and see if it is stiff or pliable.

Then I got to thinking, well heck, since I am in there, I might as well check out all the rubber too, and do the wheel bearings, and maybe rebuild the brake calipers. That way, I probably won't have to worry about those items for the rest of the life of the car.

Once I finish, I will have cleaned up the inside of the calipers ($750 each, don't want them to go south), replaced the old grease and wheel bearings with new, looked at the brakes, and checked out the state of the front suspension. Since I intend to keep the car for ever (ever being defined as "until the 500e comes along") the more maintenance moles I can whack, the better.

If I put that thing back together and the noise is still there, I will know that it is probably pads or such, since the noise is definately rotational.

thanks for the input,

Jack