Knocking sound
 

Hi folks, have a new issue that started a couple days ago on my 83 300D. In a nutshell, I get a rhythmic tapping/light knocking from the right rear wheel, but only when coasting and slowing down, and only between 15-30 MPH. Applying the brakes, or giving the car power instantly makes it go away. Turning left or right has no effect, it does not do it when accelerating, and there are no other noises, vibrations of any sort. Any ideas before I take the wheel off and crawl under the car?

Thanks

In my experience, this is caused by the rear axle (“half shaft”). Lots of info on the forum about it...

I had a Car that had a thumping in the read and it turned out to be an object loose in the Trunk. That is easy to check. Take out everthing in the Trunk and go for a drive. Don't for get the Spare Tire of besure it is bolted down.

Take an extremely close look at the rear and front Flex Discs and the Axle Boots.

The original Axles were filled with Oil and if a Boot cracks most of the Oil coms out.

Inspect the Drive Shaft Support to see if it is still in tact. The rubber rots or ripps on them.

Jack up the rear wheels and pull the rear humb in and out. If you can feel end play you likey have a bearing going bad or at least need to check the in and out play with a dial indicator.

Raise the car so that both rear wheels are off of the Ground. Make sure it is safely supported and the wheels chocked/blocked so that you can start the engine and put it in gear so the Rears rotate and safely listen and watch.
On my Volvo diesel when I did that I saw my Drive Shaft support bearing bobbing up and down. It turned out the Bearing sheild had failed ans it was full of dirt grinding around inside of it.

Thanks for the quick replies and tips......please keep them coming. The flex discs and driveshaft bearings are about a year or so old, as is the diff mount and motor mounts, but I will check them as well as the shaft and bearing. If it is a bad part I hope it is only the shaft and not the bearing. Any idea why applying the brake or adding power makes the noise disappear, or why it only happens at that limited speed range with no vibration?

Not knowing what is causing the issue means guessing. However, if something has a clearance that is excessive the part during some speeds is going back and forth within the excessive clearance.

If the load is such that it forces the part to one side and it stays there it won't go back and for knocking.

Note check you tires for blisters and tread separation.

You could also rotate your Tires and see if there is a change.

Does not answer the question but thought I would throw it in anyway. https://www.benzworld.org/forums/r-c107-sl-slc-class/2918033-replacing-torn-annular-axle-boots.html , Flexible CV Axle Boots (Benz Project) - Real Fiero Tech

Maybe one bolt in your brake caliper is loose?

First of all the rear cv joint on that side may never have seen and new lubricant for 33 years. If you can catch it early enough by removing the small clamp on the outer cv joint.


Providing the boot is still intact with no signs of leakage. Take a turkey baster or whatever. Inject a few ounces of heavy oil in between the boot and axel. Unless you find something obvious otherwise. If the noise stops you probably have caught it in time.


I have no ideal of how exactly the old heavy oil lubricant seems to deplete with no evidence. Yet it seems to do so over time in many cases.


Symptomatically the problem usually occurs after the joint warms up. Not always though as there are various ways the components can wear as well as running too dry.


Why after it warms up usually? The parts are not getting lubrication so they heat up and expand sticking and clicking as they attempt to move.


Should be done on all these old cars anyways. As preventative maintenance . When a joint gets constantly noisy is usually too late.


Nobody should want to land up owning aftermarket axles if the originals can be taken care of. They were of extremely high quality.


I will go out on a limb and say that all cv joints should have been using heavy oil as a lubricant. I have taken too many apart over the years where the grease used is no longer near where it is needed. Just a congealed soap type component pushed aside basically is all there is. The boots looked perfect with no grease leakage in the most of them as well.


Yes the joints failed. Just worn out prematurely as being under lubricated over time.

Ok, I think I found the problem. I checked the lug nuts on the right rear wheel and found all 5 to be just a touch over finger tight! The wheel has not been touched in over 2000 miles, and the lugs on the other three wheels were all nice and tight.

Lately our little town has had several instances of what I assume to be kids, messing with peoples car. Nothing outright destructive, letting air out of tires, soaping the windows, etc, minor stuff, until now!

Someone messing with the lugs is the only way all 5 could have come loose. Guess I will have to review our security camera footage for the last couple weeks and see what I can find.

Now my question, if I find that someone intentionally loosened the lugs on the wheel, do I call the police before or after I kick some serious ass.........

Small town? Drop by the station for a chat with the local LEO.'s. They'll know or have a good idea of any local kids up to no good. Also establishes a rapport with the local enforcement.

Agreed, maybe a little chat with the Watch Commander would suffice .

Agreed; do not let it pass without talking to someone.

Kind of odd thing to happen as well. Usually they steal hood stars or scratch paint etc . Or break into cars. Anyways cheap to rectify and pretty much painless as well.

The lugs if not fully tightened can work loose. I'd not leap to blame the kids.

It is amazing but I once heard a knocking sound and slowed and exited the interstate. When I looked I found I had one lug bolt left on the RR of the 300 SD...and it was very loose.

I took one each off the other wheels and limped the rest of the way with four lugs on each wheel. I cannot believe how close I came to losing that wheel!

Back in the 1980's I was on the Freeway and passed a VW Bug parked along the side of the road. Then I passed a Guy running. Up ahead of the Guy was a rolling VW Wheel. I passed all of that and don't know if that Guy ever caught up with his Wheel or not.

Now that I think about, my vote is for someone trying to steal the tire.