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  #1  
Old 11-05-2003, 07:19 PM
sdelasal
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W123 rear pinion oil seal Q {Tightening torque error!)

I'm in the middle of wrestling with my pinion oil seal. I've bought the seal, have removed the propshaft and am trying to remove the pinion nut. Here's my question.

Both the haynes manual and the MB service book (section 35-530) talk about measuring the torque required to rotate the differential and 1/2 shafts. The MB manual talks about using a 30-600Ncm torque 'measuring tool. However, when explaining how to re-install the pinion nut they adise to tighten to the figure measured and to at least 180Nm.

Well - I'm confused - 600Ncm is equal to 6Nm - so even at the highest measurement I'd expect the pinion nut to be tightened to 6Nm. Is the 180Nm a typo that should say 180Ncm?

The problem I'm having at the moment is I can't undo the pionion nut as it's on so hard. Any advice?

Steve
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  #2  
Old 11-05-2003, 09:07 PM
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Pinion nut is usually straked down, you need to check that there isn't a bit of sheet metal "folded" down to hold it.

Tightening torque and rotational torque are two different things. What you want is at least 180Nm to hold the nut -- this is the minumum -- and more if that is what is required to provide the same rotational torque as the shaft had before. This is somewhat critical, as the "washer" you are replacing is a crush design, and overtightening will collapse it too far, leading to improper pinion to ring gear clearance.

Peter
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  #3  
Old 11-06-2003, 04:42 PM
sdelasal
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If I refer to p.161 of the haynes manual, point 9. It say,s 'tighten the pinion nut gradually until the tuning torque is the same as that recorded in paragraph 2' i.e. torque to turn the flange - The light has just gone on now though as I had assumed incorrectly that the pinion nut torque should be set to the measured turning torque.

So, am I right in thinking that with the pinion nut finger tight that the turning torque will increase as I tighten the pinion nut. However, given that minuimum is 180Nm - I just need to go straight to that figure and check turning torque is in ball park.

The haynes manual says if the 180Nm can't be attained then replace the spacer - well, surely the only reason for the torque being unobtainable is the thread has stripped or the who assembly is turning.

I had not planned on replacing my spacer as a matter of course so am confused about your reference to replacing a 'washer'.


Thanks for the comments though & setting me straight!..
Steve
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  #4  
Old 11-06-2003, 06:36 PM
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I was confused exactly as you were with the the two different torque issues when I replaced mine several years ago on my 450SL. I replaced my leaking seal and ended up simply torquing to 180Nm and all is OK.
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  #5  
Old 11-06-2003, 07:14 PM
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This is a real tuff one. Actually the job can not be properly done as intended although we all do it, CAREFULLY!

The crush washer is NOT what you see under the nut. The crush washer is located on the pinion between the bearings. When originally installed the whole thing tightens up and the bearings are not tight as the inside races are spaced too far apart by the CRUSH washer. SO... one tightens the poop out of it till the crush washer crushes. This is done slowly with the bearing endplay continually checked as the inner races get close together.

The proper bearing clearance is not like the clearance of a wheel bearing. Thse bearing are designed to run under preload. SO... one tightens the pinion nut using whatever force till the bearings are so tight that it takes the smaller torque to turn JUST the pinion and two bearings.

This can not be done with the ring carrier installed and is done in original set-up.

As it turns out the bigger torque is probably less than what it takes to crush the crush washer any more. YOU DO NOT WANT TO CRUSH THE CRUSH WASHER ANY MORE. SOO... make a mark next to the original nut position (an accurate mark) and pull it to the larger torque being sure not to tighten the nut past the original spot.
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  #6  
Old 11-08-2003, 10:01 AM
sdelasal
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Thanks for your comments stevebfl. I managed to get the nut off and removed the flange to replace the seal. What I did was make a brace out of a piece of steel rod and the nut came off easy with the flange braced agains the garage floor via the rod.


What I noticed was no washer or spacer looking at me so I was going to ask - sould there be one? I think you've now answered that by saying hte crush washer/spacer is behind that bearinfg that I can see.

So, my next question. I chewed up the nut trying to loosen it with a chisel - butchery I know but we live & learn. So, I was intending to get a new nut. Either way I've lost the original marking on the nut. In that case I'm simply going to torque it up to the 180Nm spec. Now reading your post again its not clear to me whether you meant to say the 180Nm i way more than that required to originally crush the washer or, as you posted, less.

I'd be interested to hear your comments but I can't see any other option for me than to go to 180Nm.

Steve
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  #7  
Old 11-08-2003, 12:25 PM
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The concept is that the large torque will be less than what it takes to crush the crush washer. Unfortunately it can crush it, that is why the marks.

All you can do is go for it.
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  #8  
Old 11-08-2003, 09:07 PM
sdelasal
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How will I know if I've crushed it then? I read somewhere about not being able to atain the 180 figure but I can't see how this could be so as surely the nut will tighten eventually if its against a hard surface.
Steve
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  #9  
Old 11-08-2003, 10:35 PM
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Actually you will know that you crushed the washer when the differential fails in six months (or less - depends on how much you crush it).

As it turns out many differentials with pinion seals leaking already have a pinion bearing problem.

There is really nothing you can do about it now. Without a way to place the nut at its original position the best I could say would be to slowly tighten the nut with some locktite lubricating the threads. At the point of bottoming the nut, you should not have to go much father to be tight. If the nut doesn't torque linearly, stop at whatever position it stops being linear. All that is required of the nut is to mantain the inner race of the outer pinion bearing. The level of torque is just so it doesn't back off. With a load of locktite, it probably does not need to be as tight.
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