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81 300TDT WAGON , 82 300DT SEDAN, 84 300TDT WAGON(retired),
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442 Posts
Discussion Starter #1
The diff is leaking on the head connecting to the flex disc, Is the leaking caused by the seal? What is the seal called? and part number?
 

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1983 240D, 1974 240D
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501 Posts
thats the pinion seal, don't know the part number, but I think most online places have it for sale, for less than 10 bucks. I think I also saw the pinion nut for sale as well, so maybe its a one time use?

as a note, not sure how easy it is to get the pinion yoke or flange, or whatever MB calls it off one of these diffs without an impact gun to get the nut off.

Id check the FSM for the proper procedure for this since the following description may not have any relevance to MB.

For comparison example, on cube trucks, you get the nut out with a big ol' honking 3/4 inch drive impact gun and 700ft/lbs of force, then pull the yoke out with a puller, pry the seal out, clean up the surface, tap a new seal in with a soft mallet, put the yoke and washer back on, coat the threads with locktite, then crank the holy hell out of the nut so its gooooood and tight with the same 3/4 inch gun.

You would be hard pressed to duplicate that kind of force without a 15ft breaker bar and a couple guys, especially under a car. However, might be easy to break free on the MB, better have a peek at the specifications for torque and load for that nut.
 

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1979 240D 4 spd
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320 Posts
I'd have to agree with drop. The old mercs WILL have leaks. Rubber cracks in it's old age. I'd recommend keeping an eye on the oil level in the diff. Open the filler nut. The oil should be up around that level. Check it now and again and as long as the leak isn't that bad, I don't think I'd recommend tearing into it. I hear it's a bit of a job..
 

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81 300TDT WAGON , 82 300DT SEDAN, 84 300TDT WAGON(retired),
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442 Posts
Discussion Starter #4
I'd have to agree with drop. The old mercs WILL have leaks. Rubber cracks in it's old age. I'd recommend keeping an eye on the oil level in the diff. Open the filler nut. The oil should be up around that level. Check it now and again and as long as the leak isn't that bad, I don't think I'd recommend tearing into it. I hear it's a bit of a job..
yes, I will do the same as you suggested. Winter is here, no fun to get under the car now.
 

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1983 240D, 1974 240D
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501 Posts
Have a good time.
WOW thats a PITA. The heck with that, just top off the diff for the life of the car! :D

I had a diff powdercoated once, with it out of the car, I took it by a MB shop and had them break it down so I could take the case to be finished, and put it back together for me loose. Best 100 bucks I ever spent after reading that PDF!

turned out really nice, it IS nice to eliminate all those leaks if you are in there anyway, I did all new hardware and seals.
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
I have to agree, not something I look forward to, both of mine leak a bit.

That sure is blue!
 

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1983 240D, 1974 240D
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501 Posts
I have to agree, not something I look forward to, both of mine leak a bit.

That sure is blue!
"azure blue" I figured what the hey. :D At the shop I went to, all colors were the same price as black.
 

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1983 300D
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1,248 Posts
The pinion seal replacement is not that bad as it written up in the FSM. Before removing the pinion nut, You first need to determine the pre-load of the pinion bearing by finding rotational friction torque of the differential assembly. You would this by turning the pinion flange using an Inch Pound Torque Wrench and take note of how much torque it will need to turn the assembly (if the diff is installed in the car, then take the rotational friction torque with the axles installed). Then you’ll need to use an impact wrench or breaker bar with a flange holder to remove the pinion nut. Pull the flange out, then pull the old seals out and install new seals.

For reassembly, you’ll need to get a new nut because the old one would be damage from it previously strike placement. The procedure on the FSM is for when a new crush washer is used which requires a lot of torque to crush it down. Since you're only changing out the seal, the crush washer has been crushed and set already. This is where the value of the rotational torque you found earlier comes into play. You would then tighten the nut down until you come to the rotational value you got originally. It doesn’t matter if it takes for the nut to be really tight or hand tight, but as long as you get the original rotation torque value you’ll be fine. After getting the correct value, you will then strike the nut in place so it will not move.

Here is a video on how to measure the rotational friction torque that occurs in about 2:00 minutes into the video. This subject differential is a Ford 8.8 but the concept is the same in about 2:00 minutes into the video.







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1983 240D, 1974 240D
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501 Posts
think i would have still gone with black.
you're not the first person to voice that opinion :D I loved it, but don't worry, the many oil leaks on that car made sure it was liberally coated with black oil within a couple thousand miles!

Deliveryvalve, great video!

then the only special tools he would need are basically a torque wrench, a puller to remove the flange, and an impact gun?
 

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1983 300D
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1,248 Posts
....
then the only special tools he would need are basically a torque wrench, a puller to remove the flange, and an impact gun?
The flange should be removable without the puller. You'll probably need a seal puller though. But yes that's basically what you need.



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