Is my diff on its last legs? Fluid color...

JHZR2

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New Jersey
82 MB 300CD - 167k. Has sat in my garage since around 2012 due to life (kids). Started up right away, but have encountered a few issues. One is that 40-50 mph only, and only when on light throttle, I get a slight whine from the rear of the car. Let off the throttle at those speeds and it goes away. Press hard at those speeds, it goes away. Keep light throttle at >50mph and it goes away, ditto <40. So it's a very narrow band, and only with light throttle. First investigation was if perhaps it was low on oil. Zero leaks where it was parked, but wanted to see. Fluid (Mobil 1 as I recall, from 2010 timeframe) came out with a lot of entrained dark dirt. Hold it up to the sun and it was metallic. Note in the pics none of the large chunks were from this job (I didn't clean my drain pan well and it had a bit of grease and paper from a prior project). There was no metal shavings or metallic particulates in there. Any solids were sand and other grit in the drain pan. It could have been lots of cleaning. The M1 in there was the first drain and refill since I took ownership, and who knows the service status before that. I can't really see in without removing the cover. I learned of Mobil1 diff lube from this thread back in 2001: http://www.peachparts.com/shopforum...il1-synthetic-gear-lube-did-my-diff.html I've seen some dirty fluid, some with moisture in it, etc. but I'm a bit surprised by the metallic nature here. You can see in the funnel how the fluid is clear and just suspending this mess. Thoughts on the combo of this and the whine? Put AMSOIL SVG in there, TBD if it's in useable shape, but a drain and refill is easy enough.

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Messages
988
Location
Upper midwest
Did you "prep" your motor's cylinders because most likely there were/are all rusty and you have rust wedged in your ring lands now. Even with a "running" spray in intake oil prep, I question long term storage with that process. Pull the plugs on a cold engine and get Fluid Film extended door sprayer in put it in a bottom dead center cold cylinder and spray good. Do this to all cylinders and run it with the starter with the plugs out to get the Fluid Film to the sides of the pistons skirts at bottom dead center. Then do another quick spray on all cylinders with only a crank turn as not to "wipe" the cylinders with the starter running WOT wiping the Fluid Film clean. The store it for 7 years.
 
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Location
PA
I had an older BMW that sat on and off for some time. After I started driving it again the pinion bearing started making noise and eventually sounded like a siren. I think when a car (maybe German car) sits, oil drains away from the pinion bearing (which depends on splash oil to keep the oil running through it) and the pinion gear. This exposes the top of each and rust can start to occur which pits the bearing and gear surface. At this point if any damage is done it is done so run it and see if it gets worse wb
 
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22,460
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Apple Valley, California
Originally Posted by Mainia
Did you "prep" your motor's cylinders because most likely there were/are all rusty and you have rust wedged in your ring lands now. Even with a "running" spray in intake oil prep, I question long term storage with that process. Pull the plugs on a cold engine and get Fluid Film extended door sprayer in put it in a bottom dead center cold cylinder and spray good. Do this to all cylinders and run it with the starter with the plugs out to get the Fluid Film to the sides of the pistons skirts at bottom dead center. Then do another quick spray on all cylinders with only a crank turn as not to "wipe" the cylinders with the starter running WOT wiping the Fluid Film clean. The store it for 7 years.
You don't do those things to a diesel! Anything you spray in there will act as a fuel and could cause the engine to run away.
 
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6,575
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Suburban Washington DC
Originally Posted by Mainia
Did you "prep" your motor's cylinders because most likely there were/are all rusty and you have rust wedged in your ring lands now.
Where do people come up with this stuff? I thought he said it started up right away.
 

Kestas

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The Motor City
If I understand your post, you changed the fluid around 2010? How many miles since then? It couldn't have been much. After I bought my E320, I changed the diff fluid on my E320, which came out with metallic flakes. After 30K on Mobil 75W-90, I changed it again and it came out looking rather good. I should have left it in for at least 60K. Once the break-in fluid is changed, there shouldn't be much wear material that comes out in subsequent changes. That's a good amount of sludge that came out of your 300CD. It couldn't have been good for the bearings. The noise could be damaged bearings. Without any kind of inspection of the gear teeth and bearings we can only guess where the noise is coming from. Realistically, I think you'll have to just drive it and keep tabs on the rear axle... maybe change the fluid again further in the future to see how clean it comes out the next time.
 
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169
Location
Texas
I've had several cars that had that slight whine at low load and 50 mph. These were even on newish cars that had clean fluid. It's pretty hard to ruin a differential unless towing or whatever.
 
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13,087
Location
North Carolina
Originally Posted by 40w8
I've had several cars that had that slight whine at low load and 50 mph. These were even on newish cars that had clean fluid. It's pretty hard to ruin a differential unless towing or whatever.
I've had some also that just had a slight whine. Now if its loud, thats another thing. I have found some metal in there before also. I'd just run it. It will get louder if there is a problem.
 
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9,513
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Canuck living in California
The gear oil obviously looks almost brand new, so perhaps what you're seeing is some cleaning effect still going on? But those last paper towel pics show a fine metal "paste" type material too. I would like to hear back how it behaves after gear oil change.
 
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35,686
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NY
Originally Posted by andyd
I would refill with it and wait until the noise gets louder than the radio. grin2
That's in line with my thoughts.
 

JHZR2

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46,133
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New Jersey
Originally Posted by Chris142
Originally Posted by Mainia
Did you "prep" your motor's cylinders because most likely there were/are all rusty and you have rust wedged in your ring lands now. Even with a "running" spray in intake oil prep, I question long term storage with that process. Pull the plugs on a cold engine and get Fluid Film extended door sprayer in put it in a bottom dead center cold cylinder and spray good. Do this to all cylinders and run it with the starter with the plugs out to get the Fluid Film to the sides of the pistons skirts at bottom dead center. Then do another quick spray on all cylinders with only a crank turn as not to "wipe" the cylinders with the starter running WOT wiping the Fluid Film clean. The store it for 7 years.
You don't do those things to a diesel! Anything you spray in there will act as a fuel and could cause the engine to run away.
+1 Not my first trip to the rodeo with working on these old cars that have sat. It's really not that difficult to turn them over by hand via a 27mm socket on the crank. Then some cranking with fuel off. Which of course is all irrelevant to this thread!
 

JHZR2

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New Jersey
Originally Posted by oilpsi2high
Could've also been low on fluid for a while. I make it a habit to check mine by topping off at every oil change.
Was not low. When I pulled the fill plug a few drops came out.
Originally Posted by Kestas
If I understand your post, you changed the fluid around 2010? How many miles since then? It couldn't have been much. After I bought my E320, I changed the diff fluid on my E320, which came out with metallic flakes. After 30K on Mobil 75W-90, I changed it again and it came out looking rather good. I should have left it in for at least 60K. Once the break-in fluid is changed, there shouldn't be much wear material that comes out in subsequent changes. That's a good amount of sludge that came out of your 300CD. It couldn't have been good for the bearings. The noise could be damaged bearings. Without any kind of inspection of the gear teeth and bearings we can only guess where the noise is coming from. Realistically, I think you'll have to just drive it and keep tabs on the rear axle... maybe change the fluid again further in the future to see how clean it comes out the next time.
Agree. I put a magnetic drain plug in there to help keep tabs. It is pretty speculative here; I haven't gone back through all the records I have since new, but there's a likelihood that the M1 I put in replaced the factory fill or at least fluid that was changed last 20+ Years and 100k ago. The M1 in there probably had between 5-10m miles on it max. Just speculating as I've not gone back through my records.
 
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High Tax Illinois
Jump up to a 75W110 or 75W140 gear oil. Won't hurt a thing. My 2018 RAM 1500 3.21 open rear gear has little whine around 30MPH with slight throttle, let off it goes away. Doesn't do at any other speed. Some ring & pinions are just a little noisy no matter what.
 

Astro14

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Virginia Beach
I hate to be alarmist, but any whine is just plain bad. That amount of sludge and those bits of metal would have me concerned. I would pull it out and tear it down. Might sound extreme but precludes more damage... If you're lucky, it's a pinion bearing, and that can be replaced at modest cost. Your favorite Mercedes parts supplier should sell a rebuild kit. Because your W123 is an independent rear suspension, I don't think pulling the differential will be that bad. Alternatively, drive it until it blows up (and it will blow up slowly, not rapidly) and then find a good, used unit and swap it in.
 
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NH
Can you put in a borescope that is backlit? Can you test for wear if you set the parking brake? I'm wondering if the lash can be felt in the driveshaft while elevated--although this could be bearing wear and not from teeth. But still.
 

JHZR2

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New Jersey
Originally Posted by supton
Can you put in a borescope that is backlit? Can you test for wear if you set the parking brake? I'm wondering if the lash can be felt in the driveshaft while elevated--although this could be bearing wear and not from teeth. But still.
Can you explain this test more? This car squats and raises much less than my 240D when going from reverse to neutral to drive. But I don't think that's lash. In park I cannot turn the driveshaft by hand even just a slight fraction.
 
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