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  #1  
Old 06-27-2008, 02:01 PM
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'72 280SE: Dumb driveshaft nut question

The (giant!) 46mm wrench came in from Northern Tool, and so I'm making another run at getting the transmission out of the car.

The clamp nut on the driveshaft is well and truly stuck, and it's not clear from the documentation which way is loose.

Am I trying to move the 46mm nut towards the front of the car, or the rear?

Thanks!
-Zandr

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  #2  
Old 06-27-2008, 02:56 PM
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I had to think about your question for a bit. Counter-clock-wise to loosen the nut which equates moving the front most edge of the nut towards the "front" of the car
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Old 06-27-2008, 03:04 PM
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Quote:
Originally Posted by Mike D View Post
I had to think about your question for a bit. Counter-clock-wise to loosen the nut which equates moving the front most edge of the nut towards the "front" of the car
So, counterclockwise while facing the rear of the car (towards the diff).

Got it, thanks!

back to the garage...

-Zandr
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  #4  
Old 06-27-2008, 03:17 PM
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don´t forget to mark the driveshaft! and when you tighten the 46mm nut please do it only by hand!
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Old 06-27-2008, 03:47 PM
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[QUOTE=Housecrew;1895596]don´t forget to mark the driveshaft! and when you tighten the 46mm nut please do it only by hand!



No way.. that clamping nut has a Factory Torque of 20 mgk [ 145 ft/lbs] ..and it is only tightened After every thing is reassembled and the car is let on the ground and pushed back/forth a few times to set the shaft length .
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Old 06-27-2008, 04:18 PM
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Quote:
Originally Posted by Arthur Dalton View Post
No way.. that clamping nut has a Factory Torque of 20 mgk [ 145 ft/lbs] ..and it is only tightened After every thing is reassembled and the car is let on the ground and pushed back/forth a few times to set the shaft length .
Really? The workshop manual on the CD from MB says 3.0 mkp.

EDIT: The rear clamp nut on a 3pc driveshaft is indeed 20.0 mkp. But this a 108.018, I only have a 2pc driveshaft. Still can't budge the nut, though.

As to marking it...as I'm replacing the transmission, what am I marking it relative to?
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Old 06-27-2008, 04:27 PM
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Mark the driveshaft halves. They were originally balanced as one unit.
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  #8  
Old 06-27-2008, 04:43 PM
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WorkShop Manual
Two piece propeller shaft Clamp Nut.
Job 41-1-5:
Clamp nut and screws for bearing attachment should not be comepletely tightened until the car is standing in curb position and pushed back/forth several times for shaft to adjust to proper length.
Torgue settings -Job 41-0:-
Bearing atttachment bolts - 4.3 mkg
Clamping Nut at front propeller shaft - 20 mkg
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Old 06-27-2008, 06:13 PM
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Quote:
Originally Posted by Mike D View Post
Mark the driveshaft halves. They were originally balanced as one unit.
Got it. I'm not planning on separating the driveshaft, just compressing it to get the transmission out.
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Old 06-27-2008, 06:22 PM
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Quote:
Originally Posted by Arthur Dalton View Post
WorkShop Manual
Torgue settings -Job 41-0:-
Bearing atttachment bolts - 4.3 mkg
Clamping Nut at front propeller shaft - 20 mkg
Hmmm.

From 'Passenger Cars starting 1968 - Service Manual'
Page 41-0/2
(Early Model Years CD: Volume 3 - Disc 2\pdf\WM\280\grp41\41-00.pdf)

Code:
Tightening Torques in mkp

2-part universal shaft    clamping nut        3.0 + 1.0

3-part universal shaft    clamping nut front  3.0 + 1.0
                          clamping nut rear   20.0
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Old 06-27-2008, 07:37 PM
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I see that

Pre '68 - 145ft/lbs
'68-72 - 22-28 ft/lbs.
You will note also that '68 and on they want the rear of the 3 piece torqued at the 145 of the earlier versions.. I believe that is so one side of the intermediate shaft is locked tighter than the other b.c they want the shaft to stay centered. [ they require equal distant on each end at installation]
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Last edited by Arthur Dalton; 06-27-2008 at 09:28 PM.
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Old 06-28-2008, 07:29 PM
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Man, this one is fighting me. I've mangaged to move it about one flat (1/6th of a turn) and it's not getting any easier. We're sure it's counterclockwise as you face the rear of the car, right? (pull the wrench towards the left side of the car...)

I'm beginning to think that I was wrong about this transmission having been out of the car...and factory torque really was 145ft-lbs. (factory and service being different in this case)

Going to give the liquid wrench a little more time and get a cold one.
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  #13  
Old 06-28-2008, 08:09 PM
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The nut is threaded onto the front shaft. It is an angular wedge inside and as it tightens, it compresses the spline surfaces to facilitate zero backlash.
When you state "Facing the rear " ..you can be facing it either from the rear of the car or from under the car...so your orientation discription is the problem. Alway state direction as "Direction of Travel"
And right/left side on a car is always from the DRIVERS POSITION..thereby eliminating confusion for RHD and LHD vehicles and if you are in front or in back of the car. This eliminates any mistakes and is normal orintation procedure.

Look at the threads that the nut turns on ..It is RH Thread and turns as any standard nut does ..you tighten CW and loosen CCW. So, looking at the driveshaft in "Direction of Travel".[ Looking Foward from under the car} You loosen the nut by turrning it CCW. That will release the tension on the splines .
You are turning the nut the wrong direction, if I understand your R/L orientation discriptions correctly.

By turning the wrench as you state "to the left side of car'", you are tightening the nut and moving it foward. The more foward the nut goes , the tighter it gets.
You have the CD...look at intermediate bearing assembly and you can see the wedge shape design of the slide nut right in the diagram.
You tighten the nut, you tighten the backlash..you loosen the nut, you loosen the backlash...simple...
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Last edited by Arthur Dalton; 06-28-2008 at 08:44 PM.
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  #14  
Old 06-28-2008, 08:56 PM
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Quote:
Originally Posted by Arthur Dalton View Post

By turning the wrench as you state "to the left side of car'", you are tightening the nut and moving it foward. The more foward the nut goes , the tighter it gets.
Thank you Arthur! This is why I asked initially if I wanted to move the nut towards the front or rear of the car. The answer, it seems is towards the *rear* (away from direction of travel), not towards the front (towards direction of travel) as Mike suggested.

Quote:
You have the CD...look at intermediate bearing assembly and you can see the wedge shape design of the slide nut right in the diagram.
You tighten the nut, you tighten the backlash..you loosen the nut, you loosen the backlash...simple...
Frankly, the CD is horrible when it comes to illustrations of these things, and the EPC illustration doesn't help a lot. I'm sure this will all become obvious when I get it apart, of course.

Thanks again!

-Zandr
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  #15  
Old 06-28-2008, 09:18 PM
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Once apart , you will see that the outer surface for the splines is tapered, so as the nut goes up the taper [ tightening the nut] , it closes the outer splines inside circumference size smaller ..thereby tightening on to the inner spline shaft [which has a fixed circumference size].. it is a CLAMPING device employing a wedging force principle. And that force is calculated by the designers to be a specific and exact force for that application. So, they have calculated that at a specific rotational torque on that nuts threads, the wedge design will exert the required force thay want to get the proper backlash specs on the splines that they have decided to be appropriate for that shafts input .
It is specific and handtight does not make it....I have seen plenty of worn splines b/c they were not torqued for proper backlash ..same goes for the rear tranny flange nut. Guys just smack em down with a punch amd hammer [ ouch!!] and a few miles later, the speedo doesn't work [ first bad sign] b/c the clamping force of the tailshaft helix is lost and a little later the flex disc goes , along with the splines on the rear flange, etc.....
Doesn't take any longer to do it right.

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Last edited by Arthur Dalton; 06-28-2008 at 11:10 PM.
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