low groaning noise from front brakes

I get a low groaning sound as I apply the front brakes on my W115 1976 300D, especially when the car is first driven (the groaning goes away after the car has been driven for 5 miles or so).

The front brake pads are about half gone and the front rotors and rebuilt calipers are about 4 years old. I don't detect any noticeable vibration in the wheel. I recently replaced the rear rotors, calipers, and pads.

Any suggestions?

Robert

Sounds like the rotors are warped.

Inspector1,

Thanks for the reply.

Warped rotors were also my first conclusion - but the front rotors are fairly new AND I don't get any noticeable vibration in the wheel...so what's that leave??

Robert

Yes, well... I had extreme warped rotors on a Trooper with no vibrations at all, but alotta noise when I braked.
A true test would be to set up a dial gauge and check for run-out I guess.
If they are true,uhmmm, check all related front end parts, My 87 300E had a terrible groaning noise when I applied the brakes and turned left, it was the lower ball joint.

[Kestas]

Is the car driven daily?... is it parked outside?... it could be as simple as corrosion on the working surfaces.

The car is driven daily, and the driving overall is a combination of city and highway (more city driving but a long ride at least once a week with an italian tuneup thrown in for good measure).

The groaning is NOT like when a wheel bearing is failing - it is much more of a grinding-like noise than a whirring-like noise (which I associate with failing wheel bearings).

Bribenz, you may have hit on the source of the problem - but why does the noise go away once the car is well warmed up? And why would it take half the pad life for this condition to show up - wouldn't it have showed up much earlier?

Robert

bribenz,

What is the solution when the conditon you describe is the source of the groaning?

Can the old pads be salvaged by grinding off the metallic sheen...or are new pads the best (or only) solution?

Robert