The axles are only 2 years old, but like many, are of the cheap China variety.

I was concerned that the outer splines might be loose. They were fine, but at same time, I did check as best I could for slop in the axles. But only by sight. Did not notice anything.

Even before we installed the axles, I did notice a small amount of lash in the diff. But after 460k km, I didn't think it was excessive.

As best as I could check, the flex joints and u-joint were tight.

AS mentioned earlier, I did notice that I could jack the tranny up quite a bit (maybe an inch or more) without anything else moving. So first step will be to install a new transmission mount (the motor mounts were new a year or two ago)

If I still have slop and clunk after that, I need to get a shop or friend with lift to get it up where we can see what is going on.

Thanks for input from you both.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I'm going with diff also. U-Joints or CV joints generally will cause a driveline vibration.

Just a point of interest, I changed the differential fluid on a new to me '85 300SD and I swear it was filled with ATF. It poured out like water. (upon further review, an '85 isn't new to anyone ;>) )

I have the new transmission mount. Been hot and humid here, but I have got as far as jacking the car up, putting on stands and figuring out what wrenches I need. Hopefully get at it next rainy or cool day Luckily have other cars.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Finally got the mount changed (after some URO issues covered in another thread). But the clunk is still there. Louder going from drive to reverse, but does it both ways.

I need to get it up on hoist. Don't trust most shops for diagnosis on these old cars, and we don't have any MB indies locally.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Another area to check would be the differential mounts. Typically there are 3 mounts, 1 fore and 2 aft. Hard to see to evaluate. You could place a jack under the diff and assess how much slop it has. Should be fairly stiff if the mounts are still good.

We had the rear mount loose when we changed the axles. It is still in good condition. The front two mounts are what we also call subframe mounts. Can't really be inspected, but nothing apparently wrong there. I often jack using diff, so will keep an eye.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Yeah, thw 124 diff is mounted for rotational stability.
Jacking up the car from it can damage the side bushings.
So the diff can rotate a bit when put into gear.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

You can see the two rear diff bushes by looking at the rear suspension cage. There are 2x half dollar sized circular openings in the subframe where the bushes reside. These bushes have two voids in the rubber. Look at the condition of those carefully. They rarely get changed as the diff has to be dropped out of the cage to replace them. I did mine because the rubber was gone, and it clunked going into gear, and at times it felt like the rear was steering itself, mostly on acceleration.

As vstech mentioned, jacking the diff stresses these bushings.

My car is an '85 W123 300D. Does it have those openings?

Not sure what a half dollar size is! Here it would be two quarters or a Loonie cut in half

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Sorry was on mobile app and did not see your car w123/avatar, as the tread started with a w124 that's what I thought we were discussing, my bad.

As to whether the w123 has something similar? Possibly, if the diff is suspended in a cage/subframe. It's been a few decades since I crawled under a w123, hopefully other can chime in to clarify.

Best of luck on determining/correcting the source of the clunk.

Half dollar about the size of a silver maple tho worth less

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Spent more time under car today. I measured the lash in the diff. I found I could move the inner CV joint flange circumference about 1/4" without moving the drive shaft flange or the other axle. Roughly 5deg?

I tried listening with a stethoscope while rocking the jacked up rear wheels. Max noise actually came from driveshaft flange area, but that flex joint looks good, so must be transmitted from the inner diff shaft. I checked oil level and added a little.

I had car jacked up and on jack stands, but some weight still on diff. I tried starting the car and got a kind of alarming noise from under the car - tranny end. I put the car back down on wheels and the noise was still there when I first put it in reverse, but after changing gears back & forth it went away. Clunk of course still there

At 83, I am more or less at end of road doing this sort of stuff. I think I will see if someone would like to buy the car. Sad to do - we have owned it for 33 years. It has good body, only 75k miles on rebuilt engine and many recent upgrades to brakes suspension etc. No A/C. Runs very well.

So what could I ask for this car given someone would need to likely do some drivetrain work? Car is in Eastern Ontario, Canada.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Just wanted to acknowledge your noteworthy milestones. "Kudos" to you and "Congrats", as well. It is truly amazing that, at the age of 83, you're still "gettin her up on jackstands" and "crawlin' around underneath"!! Very impressive feats, indeed! I'm "only" halfway through my sixties, and can definitely envision the "end of road" for my mechanical pursuits that involve the garage floor...not "happy thoughts", by any means.

I can also imagine it's hard letting your car go. 33 years of ownership is also an amazing milestone. I'm sure that car feels as if it's a part of you, now. What a great record, though. The number of years you've owned her is almost unbelievable and a true testament to these incredible machines.

Here's to you, sir. Cheers and my hat's off! Best of luck in whatever pursuits you choose (maybe keep the Benz just a little longer)

I always read your posts and have learned a lot from what you've added to many threads....aftermarket parts from a certain 3 letter supplier not withstanding. Hope you'll continue to do so far into the future!

Appreciate the sentiments!

You are right about the 300D - It has that comfortable feeling, like a worn in pair of shoes

While diagnosing the 300D noise, I have moved to our 98 W210 (owned for 22 years) and my wife is driving the 2019 Outback (she likes to have A/C!). The 350SL (also owned for 33+ years) doesn't get driven much but still looks and runs just great.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I finally got back at 300D again after ignoring it for a while.

Today, I checked lash/slop in the only 2 1/2 yr old (5100 miles) annular axle Cv joints. Did this by first jacking and supporting rear of car so axles were in normal drive position.

-Removed wheels and bolted brake rotors to hubs.
- Marked position of inner flange vs diff so I could watch to ensure the inner end of the axles did not move.
- Rotated the rotors back and forth and determined tat, yes, there was slop!
- Marked the edge of the rotor at one point, then slowly rotated until diff end axle flange just moved. Repeated this several times and marked the extremes on edge of the rotor.

What I measured, was that the rotors are about 274mm diameter (137mm radius) and that I had about 7.5mm movement at the periphery. A little Trig using calculator said arctan(7.5/137) = 3.13 deg. So ~3deg of slop in the two Cv joint (mostly inner one)
(Repeated above for other side and got comparable results.)

I tried a similar test on bench using my original axles and found they had zero slop. A video on merc-sauce said that is how they should be.

Still don't know if this is the main cause of the clunk I hear, but I guess it is one possibility.

Next, I plan on getting car up a bit higher and re-checking the driveline components best I can.

Some say it could be a vacuum modulator issue - I will check that vacuum line to tranny is intact and cable connection is in place and not over-tight. Somehow I doubt these would be a factor.

Failing all of this, I will try and get a small shop to put it up on hoist, but doubt they will see more than I can from under car.

I am sure a competent MB shop could pinpoint the problem, but we don't have one anywhere near.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Hello Graham,
I am having the same issue on my 82' 300D with 350k miles on it. I just put a rebuilt transmission in, so I am finally ready to adress this clunk. I belive mine is worse than yours though, because it also clunks when downshifting as I brake to a stop. Makes a very nice luxury car feel old and tired.

On the chance that it will help you, here's what I have figured out:
All my flex discs, engine mounts, transmission mount, and diff mount have been replaced within the last year or 2. The axles are also remanufactured OEM axles replaced 2 years ago. So, my entire drivetrain as been addressed at this point, aside from the diff and rear brearings.

I have also made sure the transmission is in perfect tune, and all vacuum to it is perfect.

I am fortunate to also own a 240D with 196k miles. So, I compared how much rotational slop the two cars had if I rotated a wheel or the driveshaft by hand with the rear wheels off the ground. The difference is very obvious.

All of this has lead me to believe that my differential is simply worn out. I plan to replace it with a tight lower mileage unit in the next month or two. If you'd like, I can update you with the results.

Best of luck! 33 years of ownership is great. I for one would love to see you keep it, but I am biased.