Rear end thunking when coasting - Page 2 - PeachParts Mercedes-Benz Forum

Danman · #16 10-21-2013, 01:08 PM

Ive been busy with work and unable to get to the car. Today finally managed to get some time and this is what i found.

It seems the differential side bore on the drivers side has excessive play. I can grab the can and move it forwards/backwards (not in/out of the diff but parallel to it) and recreate a clunking sound within the diff. Passenger side is firm/immovable. Should there be any play of this sort or does anyone have any opinions on this kind of differential wear (output bore)?

bricktron · #17 10-21-2013, 01:30 PM

could it be the rear sway bar links? these small Z-shaped pieces cause clunking when their hardware is worn down. i need to replace mine. i'm not aware of any connection to throttle though. you can reach behind the rear wheels and see if they are loose.

vstech · #18 10-21-2013, 01:36 PM

Quote:

Originally Posted by Danman

Ive been busy with work and unable to get to the car. Today finally managed to get some time and this is what i found.

It seems the differential side bore on the drivers side has excessive play. I can grab the can and move it forwards/backwards (not in/out of the diff but parallel to it) and recreate a clunking sound within the diff. Passenger side is firm/immovable. Should there be any play of this sort or does anyone have any opinions on this kind of differential wear (output bore)?

yeah... that's bad.

any parts yards nearby? you need to change the diff.

Danman · #19 10-21-2013, 01:37 PM

Most rear end parts have been replaced, including end links. Post #1 provides a list of replaced parts.

So there shouldn't be any play in this direction (front to rear of car)? Out of curiosity, do you have any theories what could cause this kind of lopsided wear ( passenger side bore holds the axle solidly)?

Thanks again

vstech · #20 10-21-2013, 01:43 PM

there should be zero movement you can detect by hand on the axle stubs/cans
you need to source a replacement diff.
3.07's should be a dime a dozen.
if you were near me, you could have one.

vstech · #21 10-21-2013, 01:46 PM

axle stubs pass through the side bearing. if it's clunking, the bearing is bad. diff repair is possible, but it takes a crazy person (Stretch) or a very qualified shop to do it...
MUCH simpler to just swap in a diff that does not have play...

Danman · #22 10-21-2013, 02:00 PM

Quote:

Originally Posted by vstech

there should be zero movement you can detect by hand on the axle stubs/cans
you need to source a replacement diff.
3.07's should be a dime a dozen.
if you were near me, you could have one.

OK, thanks for everyone's input. I feel confident that the problem has been isolated. I will source a diff and close this thread once it is installed and problem is resolved.

Danman · #23 10-21-2013, 02:17 PM

For the benefit of anyone who may come across this thread in the future, the play in the side bore was not detectable with the vehicle on jack stands and wheels dangling. I've been under there a dozen times pulling pushing prying, trying to find excessive play or lash. This time, with the vehicle on the ground, I squeezed under there and the problem was readily apparent. I'm guessing the extreme geometry when lifted masked the problem.

bricktron · #24 10-21-2013, 02:57 PM

my bad Danman. hope that diff diagnosis helps you fix the problem!

Danman · #25 11-02-2013, 11:46 AM

Swapped out the rear diff. It made no difference. I'm thoroughly frustrated and out of ideas. I've basically worked my way through the rear end all the way up to the transmission. Sick of thinking about it at this point.

vstech · #26 11-02-2013, 12:04 PM

NFW???

new diff has no play right? axle joints may be defective... arrgh.

Danman · #27 11-02-2013, 12:28 PM

Quote:

Originally Posted by vstech

NFW???

new diff has no play right? axle joints may be defective... arrgh.

Correct, no play. I've put in 3 rebuilt axles, probably exhausted my warranty privileges and the patience of the shop in Denver.

It's definitely drivetrain. It does it in gear or neutral but have to be at speed. I find it hard to believe its in the transmission though, since its a rebuilt with under a 100k and otherwise shifts/drives fine.

Danman · #28 11-04-2013, 08:41 PM

I hate to keep resurrecting this thread but surely someone has experienced something like this in some vehicle or another.

Here's a video (not mine), but the frequency and pitch of clunking is very similar. Mines not as loud (probably couldn't get good audio) and happens when feathering the throttle, or light throttle to maintain a certain speed.

To make things even more complicated, it sometimes clunks a few times rolling to a stop, much slower almost wheel revolution. Assuming its the same thing. Wheel bearing? Transmission gear wear?

http://m.youtube.com/watch?v=25B4SFZWDRs

vstech · #29 11-04-2013, 09:18 PM

Whunter has suggested, the flex discs may have been installed either backwards, or incorrectly, or even the wrong part...

are both bolts in place on ALL of your calipers?

can you record a video of YOUR car making the noise?

vstech · #30 11-04-2013, 09:23 PM

also, he asked about drive shaft boot? is it new with the drive shaft? also, there is a bearing in the end of the driveshaft that fits into the transmission, like a pilot bearing...

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