Howl from the rear end
 

My '78 300D developed a howl one day on a drive from Jersey City to Philadelphia. It worried me to no end and I stopped three times on that first drive down to Philly to check things.

The sound doesn't happen until the car has had a few ten good miles or so of 35mph+ driving. The noise is a single tone, never going up or down in pitch, it just gets louder sometimes. It will vary volume with the articulation of the rear end and I'm sure it is coming from the driver's side wheel.

There is no play in the wheel when I try to rock it side to side to check for a bad bearing (though I admit that is not an accurate test.) When off the ground, the wheel doesn't grind at all.

My theory is that one of the parking brake shoes is becoming a little more "sticky" after friction warms it up and then it starts to vibrate the brake surface like a violin bow on a string.

Could this also be a bad CV? Both CV axles feel tight when I try to move them forward and back as well as up and down. The side to side play is there as is expected.

As I'm in Jersey City, it's illegal to work on my car in the street and I don't have a garage. I also don't have money for the repair if an indy mechanic were to do it but I definitely can't afford to be without the car.

Any thoughts on the noise? Any thoughts from north Jersey or NYC area members on where I could do the work myself?

Thanks all!
Phil Forrest

sounds like the beginnings of bearing failure... it'll get more pronounced if you ignore it.
it COULD be bad brake hoses that hold pressure and cause the pads to contact the rotor after a bit of driving.
why would a parking brake have any friction when driving? it's not supposed to be touching anything when you are in motion...

I have the same howl in my R-rear wheel...gets louder in a right hand turn but the noise stops if the brake peddle is lightly applied...Plan to change hoses soon...1980 300SD

I haven't had time to get the rotor off to check on things.
As for the brake shoe, the parking brake cable has an area where the plastic coating was worn away a few inches from where it enters the rear of the hub. Since it's been in really wet conditions lately, I thought there might have been a chance that the parking brake shoes could be stuck a bit if the cable corroded at all in the cable housing. I've drenched it with WD-40 to see if the problem would go away but since I haven't had time or space to investigate, my effort wasn't productive.

Another note is that the howl usually occurs only when I accellerate or have constant pressure on the pedal. If I'm coasting, it almost goes away entirely.

Braking will indeed affect the noise, at first it gets louder then it goes away.

Admittedly, I know I need to bleed my brakes. A flush would be be better, I'm sure. I can do that while parked in the street, cause it doesn't involve me taking anything apart obviously.

This problem just started one morning out of the blue, after we had our recent snowstorm which is why I thought about corrosion in the cable. Perhaps I have water in my brake line/s and it's causing a lock?

Thanks,
Phil Forrest

water in the lines could cause issues after it heats up and boils... a good fluid flush is advised for sure.

now the noise you are describing sounds like driveshaft center bearing/ujoint, or diff noise... loaded noise from the rear often is axle/diff releated... if it begins to clunk around corners... or if it sounds like it's only on one side of the car, then I'd lean towards axle joint failure... any chance your boots are cracked and dry?

If you don't have proper equipment I would advise 2 man approach.
Air in lines spells trouble.

cheers

.

If your caliper were sticking, the corresponding rim on your wheel would be warm/hot after driving for a certain speed.

How is your fuel pressure? i.e. clogged lines; clogged fuel tank vent.

Noise update
 

So, I flushed the brake lines in the rear of the car and the noise went away. My theory is that the water (which there was a tablespoon of that came out) was boiling and causing the caliper to compress and vibrate against the disc. I still need to do a better flush of the brake lines but the weather hasn't cooperated, nor has my schedule. For now, it's working and not making noise.
The nailing, that's a different matter for another thread.

Thanks all!
Phil Forrest