Final drive (differential) seepage on 1987 300TDT (S124)

[swogee]

The final drive (differential) on my 1987 300TDT (S124) seems to still be leaking after the replacement of many seals and parts. The leak seems to be occurring on the right side output seal.

The final drive has been serviced several times by my local MBZ shop and several solutions have been tried to correct the problem.

1) Three sets of output seals have been tried. The first two were Elring and the last was a genuine MBZ seal set.

2) New flanges were installed on both sides of the differential. (The seepage occurred with both the old and new flanges.)

3) The seals were "set in" at different depths so they would ride on different areas of the flanges to see if that would correct the leaks.

4) The final drive vent was verified as being clear and open.

5) Initially the fill was Redline 75W-90 GL-5 synthetic gear oil and this was switched to regular 80W-90 gear oil. The final drive leaked with both oils. The final drive has been refilled with the Redline 75W-90 GL-5 gear oil.

6) The fill level was correct in all cases. (All work was performed by factory trained ASE technicians familiar with MBZ vehicles.)

The owner/technician is out of ideas on what might be cause the seepage of oil since the solutions above were tried.

I am looking for ideas on what might be causing the oil seepage from around the output flange on the right side.

The only thing I can come up with is:

Crack in case of final drive? There is no obvious cracks, but a magnaflux would have to be done to check for cracks. The only solution would be a new final drive.

Thanks in advance.

-Steve

[Stretch]

Is there any lateral play in the bearings? If something is moving up against the seal I guess it could fail...

[swogee]

**Bump**

Another other ideas? IT looks like this is a tough one.

-Steve

[swogee]

Update:

The technician examined the axles on both sides and noticed that the passenger side axle seemed to have more movement (runout?) during operation which might be causing the seal to leak. The passenger side axle was replaced with another remanufactured unit and both seals on the final drive were replaced.

About a couple hundred miles later, I inspected the final drive and there was oil droplets on the axle bolt flanges. The bottom of the final drive case had some oily residue as well but no drops.

Any ideas on what might be causing the oil seepage would be welcome.

Here are some pictures:

[gsxr]

Well, assuming the level is correct (remove fill plug, fluid shouldn't run out) and new seals & flanges didn't cure it... I'd cut my losses and install a (different) used differential. They're relatively cheap, I'd probably put in new side seals and bolt it up. I've built three LSD's from salvage yard cores and never had any leaks like this. Very strange!

[swogee]

I have been keeping my eye out for a suitable differential at the PNP. It seems that the correct ratio final drive of 2.65 was specific to diesels only. Final drives with the correct ratio of 2.65 were used 6 years including 1987 300DT/TDT, 1990-1993 300D 2.5T, and the 1995 E300D.

GSXR, you mentioned a LSD core. Did you fit the LSD core into the final drives of your 300DT? Where did you find the LSD cores?

[babymog]

LSD cores come from ASD cars.

The '94/'95 E320 also had a 2.65:1, plenty of those out there. Might be a different flange on the pinion, Dave will know.

[gsxr]

Originally Posted by swogee

I have been keeping my eye out for a suitable differential at the PNP. It seems that the correct ratio final drive of 2.65 was specific to diesels only. Final drives with the correct ratio of 2.65 were used 6 years including 1987 300DT/TDT, 1990-1993 300D 2.5T, and the 1995 E300D.

That is basically correct - with the exception of the 1995 E300 which has a 2.87 gear ratio.

However, the 90-95 cars have smaller flex discs and input flanges, so you'd need to swap the input flange. This is somewhat of a gamble as you must be careful to get the nut tight enough to preload the bearing, but not so tight that it overloads the internal crush sleeve. The factory procedure specifies a rotational torque meter which basically nobody has and costs a fortune. Most mechanics mark the position of the nut and put it back in the same spot when replacing the pinion seal; this is rudimentary but apparently works ok - but I'd measure the different flanges carefully to make sure the nut should be in the same place if swapping. A list of the various US-spec diffs are on my website in this PDF file. Another option might be to swap the rear driveshaft half from the donor car. Ideally you'd get a good one from a 1987 300D/TD though, as this is the only bolt-in solution.

Originally Posted by swogee

GSXR, you mentioned a LSD core. Did you fit the LSD core into the final drives of your 300DT? Where did you find the LSD cores?

My first LSD build was for my 1987 300D. I converted an ASD diff. The cores are difficult to find, and you have to be REALLY careful to make sure that it's really an ASD diff when buying from a distance, possibly sight unseen. You need either a photo of the diff, or the VIN of the donor car to verify if it's correct.

Originally Posted by babymog

LSD cores come from ASD cars.

That is correct. And ASD was a relatively rare option. And if you buy a used one, it will need a clutch pack refresh ($$$). While I highly recommend this upgrade (especially if you notice the lack of traction from the stock peg-leg diff on wet or dirty pavement, like I did) it's NOT cheap. Expect $1k minimum, and more like $1500+. You can buy the LSD brand new from MB for about $1200, which will have new clutches, then install that into your donor diff... with new seals etc it will be $1400-$1500 plus the cost of the donor diff. The part number varies with gear ratio, see page 4 in the above PDF. Although MSRP is $1640, you can get it from parts dot com for ~$1127 plus shipping (choose "Freight-Quote" at checkout to avoid the flat 15% S&H fee).

Originally Posted by babymog

The '94/'95 E320 also had a 2.65:1, plenty of those out there. Might be a different flange on the pinion, Dave will know.

Yes, most of the late M104-powered W124's have 2.65 ratios, as seen in my PDF file. However these are larger 210mm diffs. It should be possible to swap that in but it won't be easy, once again the input flange is different, and when it's all done it just adds extra weight for the stock engine to turn (but it is a nice upgrade if you're building a SuperTurbo). If you use one of these it has to be from an ABS car, not ASR, as the ASR cars do not have the provision for the pinion speed sensor required on the '87 300D.


There are a couple 1987 300D diffs available from a salvage yard in SoCal for ~$250, M&M Imports. There's one in San Jose (American Imports, an oxymoron, no?) but no price listed. Another is in Santa Clara. Might be worth a couple phone calls...

[babymog]

I have one sitting on the shop floor in Michigan, ... probably not worth the time and $$ to ship though.

[gsxr]

Originally Posted by babymog

I have one sitting on the shop floor in Michigan, ... probably not worth the time and $$ to ship though.

Ship weight is approx 75 lbs, cost to ship cross-country would be $60-$80 via FedEx Ground. You need a heavy-duty box with very good packing.

I have one too from my blue '87 but it was developing a slight gear whine, so it's not really saleable (and, it's got ~275kmi, lol). I was keeping it for parts. Oh yeah, almost forgot, there's a good diff in my white '87 parts car but I plan to (eventually) sell the parts car complete, i.e. running and able to move under its own power.

[babymog]

I don't really want to ship anyway, ... and it's still connected to the subframe with axles, easier to scrap it. They made more, LOTS more, and I'm betting that there are a couple-hundred in junkyards in CA.

[swogee]

I figured I would post an update on the final drive seepage problem on my 300TDT.

Back in Sept 2010, the shop that was doing the work on the final drive examined the axle shafts, as well as all the related parts that were connected to the final drive. The shop replaced under warranty the passenger side axle shaft since it was determined that the run-out was excessive. (Axle shafts are rebuilt units.) The master tech/owner felt that the excessive run-out was the cause of the seepage. In addition the flange seals were again replaced on both sides and the bearings were checked for excessive free play. (The free play was determined to be acceptable.) I thought the seepage problem would be resolved, but in a couple weeks I noticed there was oil splatter on the exhaust pipe and seepage on the bottom of final drive as well as oil on the axle flanges of the final drive. I took the 300TDT back to the shop and they again inspected the final drive, but they didn't think the oil was excessive.

Fast forward to Feb 2011, I am installing the factory trailer hitch and notice there are droplets of oil on the bottom of the final drive and there is oil splatter on the exhaust pipe and oil on the axle flanges. I bring the 300TDT back to shop again and they inspect the final drive and this time they confirm it is indeed seeping again. At this point the recommended course of action is to swap out the final drive for another unit. It still kind of bugs me that the cause of the final drive seepage has not been actually determined. I am an engineer and I like to know what is causing a failure before attempting a repair solution to ensure that the solution will actually correct the problem but at this point there isn't anything else to try.

I have started searching for an ASD differential from a 1990-1993 124.128 but so far I haven't had much luck. I figure if I am going to swap out the final drive I may as well make upgrade to LSD.

As a side note, there are a few other things to note that may or may not be related to the final drive seepage. The rear subframe bushings are cracked so those need to be changed out at some point time. Also the driveshaft bearing support seems to be wearing out at an accelerated rate. The last one that was installed lasted less than two years, and before that it was less than four years. I did start a thread on the bearing support to get ideas on the cause of failure as well.

Any thoughts or ideas are welcome.

Thanks in advance.

[Stretch]

Have you been monitoring the oil level in the differential?