W115 strange, loud, intermittent sound

[luketmarx]

I have a '76 w115 240D, manual trans.


In the last 200 miles or so I have heard a very loud sound about 4 times, happens perhaps once very 50 miles or so.


I've had it happen at 40mph or 70 mph, I think any speed would do it.


What happens is very faintly I hear what I think is a harmonic metallic sound for maybe 2 seconds, then it quickly builds to an extremely-loud-someone-must-be-holding-a-railroad-spike-to-a-spinning-surface or something crazy like that..last for another 2 seconds, then all is normal again. Scared the crap out of my wife too.


Any ideas? Quick peek under there and nothing was dragging or had fallen off. Seems to drive normal, although my wife thinks there's a vibration there that wasn't before...


Thanks!

[Mike D]

Speedometer?

[luketmarx]

No, way louder than that. Also, doesn’t seem to be coming from the instrument cluster. More underneath or behind.

[tyl604]

Sounds like your speedometer cable is going bad. I had a 1970 6.3 years ago and had that problem. It was a very loud, rasping, grating kind of sound. Would go away for a while and then just come back.

[cth350]

visual inspection of the transmission, mounts, flex disks and drive shaft show no signs of scuffing, looseness or missing bits? -CTH

[luketmarx]

Ok, update. I didna good look over of the undercarriage and saw nothing unusual. I replaced all brake pads, because they were worn out. Drove it today, and noise came back-from the rear.

Then my left rear wheel locked up on a freeway on ramp. And here I am on the side of the road, waiting for a tow truck.

Where do I start when I get my car back home? Thanks!

[tyl604]

Can you post a recording of the sound?

[pj67coll]

Originally Posted by luketmarx

Ok, update. I didna good look over of the undercarriage and saw nothing unusual. I replaced all brake pads, because they were worn out. Drove it today, and noise came back-from the rear.

Then my left rear wheel locked up on a freeway on ramp. And here I am on the side of the road, waiting for a tow truck.

Where do I start when I get my car back home? Thanks!

I have an unexplained, intermmittant noise that "might" be similar to what you describe. I suspect a rear axle shaft. And am most interested in what you will find out when you find out what your issue is.

- Peter.

[rocky raccoon]

Had similar. Look for a missing brake caliper mounting bolt. If you re-used the bolts without renewing the LokTite last time you had calipers off one of them may have come out. This allows the caliper to swing and jam the wheel when brakes are applied.

Almost sucked the seat cover into my rectum when it happened to me.

[luketmarx]

Ok, got a chance to look at it. Wheel off, Brake caliper off, no problems with the caliper. Brake disc off. Drum parking brake looks rusty, but looks OK. Axle CV joints are most likely OK, because the seals are still intact. Although they are weather-worn and should be replaced soon. I guess now is a good opportunity.

So I'm suspecting wheel bearing. How do I get to it? Do I need to remove the rear diff and axles, then use that large specialty nut I saw a little about when I did a bit of research?

[luketmarx]

I removed the bolt at the center of the hub and tapped the axle almost all the way out with a brass drift, but it won't go entirely out. Do I need to remove the rear differential to get the axle all the way out?

I'm out looking for the specialty socket now..

[cth350]

what was the source of the lockup? was it the brake pads being applied or a further evolution of the original problem?

-CTH

[luketmarx]

It seems to be the wheel bearings. Locked up solid, even with axle disconnected as much as I can.. I'm having major trouble removing the axle. I'm going to post a new thread asking for help/tips.