Or is it more of a rattle?

I've got a 64 Sedan Deville, which had around 25,000 miles when I got it, three or four years ago. 

It's up to maybe 28K now.  In the last year, it's developed the most obnoxious clunking or rattling noise in the rear end of the car.

Some background:  I'm a mechanic who has done well wrenching on commercial diesel engines, and I have a small mom and pop type shop that I run in my spare time.  I've been extremely successful, but this noise is eluding me.

I do not have a drive-on lift.  I only have a lift that will pick up the car by the frame. I'm not sure if this is part of my problem.. I have had a really tough time duplicating this noise.

With the car on the ground, you can jump up and down on it, and rock it side to side so hard that the wheels slip back and forth, and it will not make the noise.

It only occurs when a back wheel hits a bump, on the road.  Speed isn't a factor. When it hits a bump, there is a sort of "kuh-klunk" that follows the bump, sometimes it makes the clunking noise three or four times. 

I replaced the original shocks a few weeks ago, figuring they were shot.  They were.  The ride was greatly improved, but no change in this noise.

Today, after doing a bunch of reading and ordering the part, because why not, I replaced the rear ball joint. I regret replacing it, because the old one wasn't bad, but I figured the wishbone was off anyway, and I had already bought it. 

Now, breaking all my own rules, I replaced the ball joint without really checking it, since the noise SOUNDS like a ball joint clunk, and every single bit of information I gathered about this noise online pointed to it. 

Noise is still there.  All of the bushings in the back of the car are still in good shape.  There's a little bit of cracking on one, but they are all nicely centered, and I can't get any of them to move very far.

The exhaust, driveshaft, etc, etc are all secured, all hangers are good, all rubber is good.


Today, I decided to pick it up again, and set the rear end down on jack posts, so I could wail on the tires with a sledge hammer, trying to duplicate the noise that way.. trying to simulate what happens on the road.  No luck.

But then I started banging around with my fists.  I can (perhaps) reproduce the noise by banging on the end of the wheel. 

Could this noise be INSIDE the rear axle?  Could it be the rear wheel bearings?

I am open to any and all suggestions. I troubleshoot and repair complicated problems all week, and am being defeated by a simple noise, and It's driving me crazy! 

Thanks for reading!

Aaron

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 Aaron , my first thought was the rear ball joint/yoke ass'y. I'm sure you've checked the differential oil level & condition of the oil.  Seems like probably wheel bearings or pinion bearing. I think I'd disconnect the driveshaft  and check for play at the pinion bearing . I'm by no means an expert, but that  would be relatively easy to check.

The diff oil was a little bit low, but not terribly.  The pinion seal leaks a little bit.  The differential seems nice and quiet, and I don't feel any play with the driveshaft connected.  I have not removed it and checked, but anything is possible.  The angle of the driveshaft could well be keeping it tight with the vehicle raised on a hoist.

Actually, I don't hear ANY rotational or bearing type noises with the car, although I did notice that, while rotating the right rear wheel, I could hear a bit of bearing noise.  So they need to be replaced regardless.

It just seems odd that it could create such an obnoxious clunk, as there is little to no play.

If you replace the rear wheel bearings only buy SKF. National and other brands have failed on occasion. Rockauto usually have the SKF bearing.

Sometimes a sound is believed to be coming from an area when its coming from another. Maybe if you could have a friend test drive the car, in a secure location, with yourself "leaning out" the passenger door listening to any sound? It could be a nice stunt trick and we all are awaiting the U-tube film... :-)

One easy thing to check though. Is your center bearing in good condition and the center bearing support secured tight to the frame by the two bolts (18 foot-pounds)?

I grabbed the driveshaft where I could get ahold of it at both ends.  The problem is, with the vehicle supported on the lift, the rear axle is dangling, putting a lot of pressure on the driveshaft.

The noise is coming from behind though, behind the rear seat, under the car.

I did have someone else drive it, while I sat in the back seat. 

Something else to consider is a body mount.  I had the same problem with my 66, only over some bumps, I thought maybe it was something moving in the trunk or even the exhaust slapping the chassis, but when I got under it, I saw, just above the spring perch over the rear, a little wear mark on the bottom of the body and shiny spot on top of the frame, from where the two would meet when the frame flexed enough.

I don't know that this is your problem, but it's something to consider. if you cant find anything else.  

This is exactly the same type of noise. 

I will have to look harder, but I have looked between the body and the frame over the whole length of the car, and especially in the back. 

When this started, I was almost sure there was just something banging around in the trunk. 

I've almost considered riding in the trunk....

Get a go pro camera and film the pinion angle. The bushings on the lower arm are probably shot. The frame bushing thing is a good lead too.

Good suggestions. Other than make sure everything is tight (eg. shocks, coil springs, exhaust pipes & hangers, etc), I was ask is there anything in the trunk actually jumping around (e.g .tools, jack, etc.). I've got the Ecalade EXT with the enclosed trunk bed and don't know how may times I will forget I have something back there like a loose 2 wheel hand cart, and be just riding around and here a clunking sound when I hit a bump and get real nervous until I remember I had something in the back. 
Other than that it sounds like you are getting the noise when the tire suddenly goes up and down over a vertical bump. With that in mid I might find a nearby speed bump and have someone drive the car back and forth over a speed bump while you stand near by and see if you can perhaps isolate the sound. It would be hard to duplicate the up/down motion of a speed bump up on a lift or by just hitting the tire and think you need to run it slowly over some bumps.  There are things such as worn out drive shaft CV joints, busted center member bear support bearing bracket rubber, loose shock mount nuts, improperly installed coil springs, body mounts, etc, that you should be able to confirm one way are the other with a good light and pry bar. Let us know what you find out. 

I'm going to empty the trunk completely just to rule it out. There's not much in there, other than the spare tire, and the jack- parts that came with the car originally, and have been in there for duration.  Plus, riding in the back seat, it sounds distinctly like a sound from UNDER the car, rather than behind me, but I'd be a fool not to rule out any possibility at this point.  It wouldn't take much to remove the jack, tire, etc, just to be sure, although I've verified that these are tight in the trunk. 

I like the idea of rolling the car over a speed bump.  I'm going to find a pothole or something and verify that I can reproduce the problem on demand.  There are not any speed bumps in my area, as I live in a rural area.  But I can certainly put a 2x4 across the driveway and use that, or create something that might duplicate the problem. 

This is an ultra low mile car, so wear and tear isn't much of an issue.  My jaw just about hit the floor after I removed one of the rear brake drums just for a peek- clean, hardly any dust, and even the springs securing the shoes still showed fresh paint!

But certainly, there are items that fail as a function of age instead of use.  I understand that 100%, but am hesitant to "shotgun" replace parts.  I felt bad about replacing a good rear ball joint- but I had already bought the part and had the wishbone out. 

I live in central NY state, and for the last few years have taken this car on a few trips through the Adirondacks as the seasons change.  It's really a great driving, and surprisingly fuel efficient car.  I'd like to get it sorted out before the fall leaves change, and time is moving fast. 

I originally grabbed this car as a flip, but I've grown to really like it.. and have no intentions to sell it now.  




I guess I might have been up close to you when we were at the 2014 CLC Grand National in Lake George. Really loved that area. I think we would have been east of the Adirondacks.

Yes, Lake George is in the eastern part of the state, but you were within about two hours.

Glad you liked it.  It's nice to know that people from other parts of the country realize there's more to NY than smog and tall buildings :)

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