500E - Humming Sound at 30-50 from Front
 

My 1993 500E with 115,000 miles has a had a periodic and very subtle humming sound from the front, that sounded too high in pitch to be from power steering, since I bought it at 110,000 miles. It would appear for a matter of seconds disappear and then reappear.

Today, I noticed the sound to be much louder and almost constant. I then noticed that, if I lightly tapped the brakes, it would abruptly stop. The front brakes have about 25-30% material left, and the rotors will be due for replacement when the pads get replaced. There is no pulsing in the braking, which is altogether smooth. Any thoughts appreciated.

P.S. To those of you who helped me with my previous battery drain problem, I've not gotten back to trying resolve it and been using using a very nice little shut off switch on the negative terminal as a temporary resolution.

Bearings.

Yep, sounds like bearings.

Deal with them quickly, otherwise you may need to replace the spindles.

FWIW: replace the bearings, don't just re-pack with MB grease.

:-) neil

One quick additional question: When I tried yesterday night to replicate the noise after the car sat still for 4-5 hours, I couldn't do it in 15 minutes driving, even while making sharp turns trying to load the bearings up one at a time. Later, after straight driving for about 20 minutes, the humming recurred. Is there a temperature that needs to be reached? Does that confirm or point away from the wheel bearing diagnosis?

Thanks for your patience.

By any chance, do you have the early alloy Brembo brake calipers? If so, that may be the issue as they will make noise, especially as the pads wear.

Thank you. Your suggestion is consistent with a thought by a very good independent Mercedes mechanic who drove the car yesterday, but evidently was not aware of the calipers you describe. I will look at them tonight. If you have time to respond, being the lazy person I am, is there a marking or characteristic I can look for without pulling a wheel?

The alloy calipers are finished in a smooth, semi-gloss black paint with a white Mercedes Star clearly visible. I'll see if I can find a picture...

See post #5 here: http://www.500ecstasy.com/forums/showthread.php?t=434

The early production 500Es had Brembo front calipers as shown.

The reason MB replaced the aluminun 4 piston Brembos with 500SL cast iron calipers was to address a complaint from customers - as the pads wear, a vibration (or humm or growl) occurs between 30 - 50 mph. Litely tap the brakes and the problem goes away. This 'complaint' does not affect performance. I have experienced this 'complaint' twice ... both times when the pads were about 50% worn. We the pads where replaced, the sound went away.

Good luck.

I have had a humming sound coming from the left front, also. It will not do it when at the tech's. It's not the wheel bearings. I have not tried tapping on the brakes. It comes on at all speeds, and is not speed-dependent.
My tech checked out all the front end parts, and it was not that, either.
Tom
92 500E
132,500 miles

Tom, Norman, Glenn, Everybody: Your responses are helpful and reassuring, as I my schedule prevents brake and/or bearing work in the next week.

Tried tapping my brakes, and voila, the humming went away! Sounds like the calipers to me.

Tom
92 500E
131,000 miles
a relieved guy - I hate it when unidentified noises come up - they usually mean $$!

Tom: Thanks. It appears we have double confirmation of the diagnosis now, and can drive a few more miles before necessary work.

Easiest way to check for alloy vs steel calipers is to take a kitchen magnet, reach through the hole in the wheel, and see if it sticks to the caliper. If it sticks you have the steel calipers. If it does not, you've got the sometimes-known-to-humm alloys.

Hope this helps,
Lee

So is the only fix replacing the calipers?

Tom
92 500E
132,000 miles and climbing

No ... don't give up on them! Install some new pads ... easy and cheap fix (relatively speaking). I have a couple of theories I'm going to try when mine start talking. Stay tuned ~ 3-5 months.

If you do change out the Brembos, do give us a chance to send them to a nice home ... :D