1987 300 SDL rear end noise
 

I have a 1987 300 SDL TD with 125K that has an annoying hum(sometimes howl) coming from the rear part of the vehicle. When you tap the brake, the noise stops and may not come back but on the other hand may continue a few seconds after the brake tap. Every time I tape the brake the noise will stop only to start up again.
The vehicle is not driven a lot. I took off the rear wheels and inspected/cleaned the rear rotors and pads. That seem to help for a little while but the hum came back.
About 5 years ago the left rear brake caliper was replaced because it had seized up.
I have had people tell me that the problem is with the brake pads or with the brake caliper not releasing the pressure on the pads. I have had the vehicle for 10 years. Another person told me that the brake fluid needed to be changed and that was causing continued pressure on the pads. I have checked the rear wheels by touch and do not sense any out of the ordinary heat build up.
I would appreciate help from anyone that has had to deal with this issue.
Thanks. :confused:

You need to sell me that car:D;).

I would start by removing the rear tires and doing a good visual inspection to see if there is anything obvious. Inspect all of the brake components. Not sure what a howling noise is (althought I did see the movie). When was the last brake job?

If you take the vehicle up to 55 mph, will you hear the annoying hum continuously at road load?

If you let up off the pedal very slightly, so that the vehicle is barely slowing down, will the hum go away?

If you let up off the pedal completely, so that the vehicle slows down normally, will the hum change pitch or go away?

If you press down on the pedal and accelerate, will the hum be reduced or go away?

The answers to these questions may point to something other than the brakes.

Will try the suggestions
 

Thanks for the advice. I will do the test and report back. Maybe a discription of the noise is more of hum than a howl. Listening to it makes one want to howl. :)

A dieing wheel bearing?

jrmurray,

Tried everything with mine that has been suggested above.. loose parts, tire noise, etc, etc.

I gave up and took it to the tech I use who used to work at an MB dealer. He said the only thing left was to change a wheel bearing. The old bearing looked brand new when it came out :eek:

Noise never went away. Stayed exactly the same for the next 6 months.

I got upset and took it into my own hands. First thing I did was to drain & refill the rear differential fluid with full-synthetic (not sure of the brand, but I think it was Mobil 1)

Problem disappeared. I have now put 40,000km (25,000miles) on the car over the last 1.5 years and the problem never came back. It's dead silent now!

Change the fluid first! If it works, wait a few months and change it again to make sure all of the old stuff is out, and you should be fine.

Neal

Sdl rear whining noise
 

My sdl is doing the same thing- what weight of synthetic oil did you use in your rear diff. ?- i'm surprised that would make the difference- i was suspecting the center bearing on the driveshaft- by the way- anyone intersted in 1986 300sdl for sale? 215k miles- smoke silver w/burgundy leather- 17 years of ownership- it's a peach- give me a call- 207-632-6894

I don't remember what the weight was. I looked up the specs for proper weight differential lube for the car, then went to Walmart and bought Mobil 1 that was exactly that weight.

Try changing the fluid first.. I figured it was a $20 experiment and it saved me a whole ton of headache. Honestly, if the wheel bearing didn't fix it and nobody knew what to do (short of suggesting changing the differential), I would have probably given up and sold an otherwise perfectly good car.

Someone would have bought quite the bargain car, considering they would have changed the diff lube first and never had a problem :)