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560SEC / 850CSI / 525i
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73 Posts
Discussion Starter #1
Noticed my Diff leaks from the driveshaft side. I need to replace the rear Flex disc anyhow, can I just undo the retaining nut, then the flex disc mount and pop in a fresh seal (already purchased) when Im there?

Found this good thread which had the diff out at the time, but looks like it could be done when installed on the car too?
 

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One Smoke Silver '87 570SEC, one Black Pearl '87 560SEL
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4,504 Posts
If you don't have to pull the pinion shaft, then it might be possible. Removing the pinion shaft is done with the diff on a bench. The diff weighs right at 100 pounds so while unbolting it isn't particularly difficult, it really isn't a one-man job.

FYI, those six allen bolts that hold the axle flanges to the differential flanges are the toughest bolts to remove I've found on the car!! The only way I've been able to get them out is a 1/2" impact gun capable of over 400 ft/lbs of torque running at 120 psi rather than the normal 90 psi. Even then the gun has to hammer for a little while to convince those #$%^& bolts to let go.
 

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1983 280se
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40 Posts
You will have to make a tool to hold the flange while you undo and do up the nut (a large plumbers pipe wrench might do it) the nut will be tight !! you should mark the flange and nut so when it all goes back together you get the same preload on the bearings (theres probably a collapsible tube between the two bearings) I would go a bees knee tighter than the marks - there is a way of testing the preload with a spring scale and a piece of string wound around the flange (a certain amount of force required to move the flange) but I am pretty sure the driveshafts would have to be removed from the diff to get the correct preload. The preload determines where the pinion sits in relation to the crown wheel - you do not want to change this - eg howling diff.
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,993 Posts
Noticed my Diff leaks from the driveshaft side. I need to replace the rear Flex disc anyhow, can I just undo the retaining nut, then the flex disc mount and pop in a fresh seal (already purchased) when Im there?

Found this good thread which had the diff out at the time, but looks like it could be done when installed on the car too?
Yeah, that's my thread and I've done the job twice. I had help doing that font seal, and it was a bitch. First off you need a special socket to remove the tail piece. Then the seal needs to be pressed out and a new one pressed in. It was not easy in either case.

I would recommend doing it right and remove the Diff. But good luck if you don't!
 

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1968 gto (sold) , 91 volvo 740, 89 $300TE, 89 560SEC
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432 Posts
I truly don't think its possible without r/r the diff itself. As previously stated it does take a special tool to remove the flange nut, also great care should be exercised not to alter the pre-load. The bolts for the axles required a triple square socket (at least on my 89 SEC). I use a long pull bar to break the axle bolts loose, and they are tight as hell!

Its really not bad to r/r the diff. If the pinion seal is leaking; you may as well replace the axle seals while your at it... Do it once properly then forget about it.
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,993 Posts
I truly don't think its possible without r/r the diff itself. As previously stated it does take a special tool to remove the flange nut, also great care should be exercised not to alter the pre-load. The bolts for the axles required a triple square socket (at least on my 89 SEC). I use a long pull bar to break the axle bolts loose, and they are tight as hell!

Its really not bad to r/r the diff. If the pinion seal is leaking; you may as well replace the axle seals while your at it... Do it once properly then forget about it.
+1 on that. Also, you need to press in that front seal and we had to use a big press, so it had to be out.

The only problem I encountered was the big 10MM bolt that goes vertically up into the diff. Also use care when removing the eight hex bolts going to each half shaft and be sure o use blue thread locker when reinstalling them.

Do it once, do it right.
 

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560SEC / 850CSI / 525i
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73 Posts
Discussion Starter #8
Just to update, thanks for the replies, looking at it Id say its weeping on both halfshafts too, might as well leave it and do it properly later.
 
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