Author Topic: Rebuilding LSD clutch disks 6.9  (Read 755 times)

rumb

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Rebuilding LSD clutch disks 6.9
« on: 21 November 2019, 12:10 PM »
I finished disassembly of the diff.   

1. remove ring gear with impact wrench
2. punch roll pin out from diff shaft
3.knock out diff shaft with brass drift
4. use axle to roll diff gears so you can take the small gears out
5. remove side gears along with the clutch disks

Observations
1. as you can see my diff shaft and inside diameter of one of the small gears are scarred - good news is MB still sells them.

2. The ball washer on the small gears was nylon whereas the ones I had previously purchased are steel.  They are at least shaped the same so hopefully they will fit.  The diff in the carrier was not loose at all.  ;D  The ball washers are now NLA so I am glad I bought them over a year ago. 140-353-01-24.  Strike that thought. That washer is for diffs from #137831 and my diff is much lower than that. Looks like I will be reusing the nylon ones.

3. My clutch disks are very worn. quick measurement is each one is .1 mm thinner which would be .5mm total on each side - 1mm total both sides.  I measured the torque before disassembly and it was about 5.5NM and spec is 25-35NM.  More about that is another post.... You can see in the picture where the lining is completely worn off in some areas.

4. you never really get used to the smell of diff oil. :o

5. I found a fleabay source that sells the clutch discs. I will be ordering them today.  The double sided ones A1293531162
( and flat plates A1123530662) are used on :
C107   
C108   
C109   
C111   
C113   
C114   
C115   
C116   
C123
C124   
C126   
C129   
C140   
C201

Absurdity that MB no longer sells these.
« Last Edit: 21 November 2019, 12:50 PM by rumb »
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #1 on: 21 November 2019, 12:26 PM »
Now onto the big question.  The W116 manual says the torque spec for clutches is 25-35NM but the W126 manual say 80-160.

Since the clutches are the same and as far as I can tell the internals are the same why the different values?  Did MB upgrade it because the W116 wore out so quickly?
« Last Edit: 21 November 2019, 12:32 PM by rumb »
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

TJ 450

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Re: Rebuilding LSD clutch disks 6.9
« Reply #2 on: 21 November 2019, 07:26 PM »
Nice work Rumb,

Just out of interest, what sets the preload on those side bearing, is it the washer on the axle shaft? Or is it fixed by some other manner?

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #3 on: 22 November 2019, 05:30 AM »
The preload is set by how thick all the clutch disks are, or more correctly the drag on all of them.  The drag on all of them is the torque needed for the LSD to slip and allow the diff to operate as an open diff when you turn corners.  MB supplies different thickness of the single sided clutches - one on each side- to change the drag.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: Rebuilding LSD clutch disks 6.9
« Reply #4 on: 22 November 2019, 07:24 AM »
Impressive work, Robert!  I'd be terrified to take on that job.  What motivated you to do it?  Were there symptoms or was it just in the spirit of having a brand new car?

-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #5 on: 22 November 2019, 08:22 AM »
I'd wager that almost all 6.9's the posi traction is worn out on them.  Easy enough to test.  raise both rear wheels off the ground, neutral and parking brake off, turn one wheel by hand.  If the other side turns in the opposite direction then it is worn out.  They are suppose to turn the same direction.

I've rebuilt the rest of the entire rear subframe/attached components so this was the last piece, plus I needed to replace the axle seals on the pumpkin anyway.


I guess when I am done I want to burn rubber on both rear tires!
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: Rebuilding LSD clutch disks 6.9
« Reply #6 on: 22 November 2019, 02:37 PM »
I'd wager that almost all 6.9's the posi traction is worn out on them.  Easy enough to test.  raise both rear wheels off the ground, neutral and parking brake off, turn one wheel by hand.  If the other side turns in the opposite direction then it is worn out.  They are suppose to turn the same direction.

I've rebuilt the rest of the entire rear subframe/attached components so this was the last piece, plus I needed to replace the axle seals on the pumpkin anyway.


I guess when I am done I want to burn rubber on both rear tires!
Sing hallelujah!  Read your post just as I was about to leave the garage so I went back and tested.  It passes!  Must be an early Xmas present.  But now I wonder for how long? ::)  Thanks,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

TJ 450

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Re: Rebuilding LSD clutch disks 6.9
« Reply #7 on: 23 November 2019, 07:53 AM »
Rumb,

Interesting, so if the clutch discs are worn this will cause those bearings to have excessive play?

I swapped the diff in my car as the original was extremely noisy only to find the replacement only slightly less noisy. There is at least a mm of play in-out at the spline of the half shafts. Just curious if that would cause the noise. I have a third unit to play with so I may look at rebuilding it.

I have also noticed it's only the 6.9 diffs that make this loud noise.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #8 on: 29 November 2019, 01:14 PM »
Interesting, so if the clutch discs are worn this will cause those bearings to have excessive play?

I swapped the diff in my car as the original was extremely noisy only to find the replacement only slightly less noisy. There is at least a mm of play in-out at the spline of the half shafts. Just curious if that would cause the noise. I have a third unit to play with so I may look at rebuilding it.

I have also noticed it's only the 6.9 diffs that make this loud noise.

The side bearings wont be affected by anything as they are captured with the race on the outside housing.

I think there could be half shaft movement as the clutches wear as the clip in the end of the shafts is inside just next to the larger gear. - my rough measure was .5mm on each side would be possible with mine. Dont forget that there are shims that go on each side - on the outside-  to take that slack out. they come in different sizes. They are matched to the half shafts, not the diff.

6.9 is the only diff with LSD I think.  Noise could come from the internal diff small gears or from the large ring and pinion if they are worn. On my parts car parts the inside diff has a lot of movement on the small gears. My driver there really isnt any play. I never drove the parts car so I dont know if it was noisy or not.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #9 on: 29 November 2019, 01:20 PM »
I've been trying to decipher the different torque values on the clutches. To me it would not matter what chassis they are on - w116 vs w126 or R107  as they only spin when you turn a corner and the inside tire has to move slower. The breakaway force would be nearly the same on either chassis perhaps variable to a degree by the tire diameter that would change the torque applied by each wheel.

I received the new clutches and am trying to figure them out. I have sent a question to the supplier to see if I can get any advice.  Them came with no instructions.  The order form said "drop in replacement"  which isnt to me at this point.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

slfan

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Re: Rebuilding LSD clutch disks 6.9
« Reply #10 on: 30 November 2019, 02:39 AM »
Will need to raise the car and check this.  Thanks for the information.
1978 - 450SEL 6.9 - 3170
1978 - 450SEL 6.9 "Parts Car" - 2973

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #11 on: 12 December 2019, 09:24 AM »
Progress of sorts.

I followed the suppliers advice and put in new  plate/clutch/plate/clutch/clutch/plate/clutch/clutch/plate/clutch/plate and had a total fail. After you put the big gear with all the plates/clutches back in the housing you then need to wind the small pinion gears in. You first roll one gear in all the way to to bottom and then you are suppose to put the other gear in and wind in back in the opposite way to the ending position.  Problem was that 1. I took his advice and 2. I half ass measured the new and old stacks and it ended up @3.64mm too thick so the first small gear got stuck in the housing. With assistance from local shop they got it out.  I suggested they just take a torch to the small gear and cut it in half.  :o

So today made a spreadsheet and tried different combination of old and new parts plus what can be had from MB for the end single sided clutch and I think I found a potential winning combination.  When I first took the diff out the clutches spun freely. I now will have 2 possibilities to increase the packs by .22mm or .32mm.  Hopefully one of those combinations will provide the correct setup.  Parts ordered today from MB.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #12 on: 29 January 2020, 12:04 PM »
I finally was able to complete this.

I originally order this clutch pack set on ebay:
https://www.ebay.com/itm/Clutch-plate-set-for-Mercedes-W126-R107-210mm-Large-case-LSD/264197888116?hash=item3d836bd874:g:6fUAAOSwAvNcaEif

There are only a few thicker end single sided clutches available from MB.

The clutches and plates were both thicker than the MB ones. I ended up using the new clutches and original plates. With these I still could not get the setup correct.

I ordered custom shims from McMasterCarr .003" thick in the shape of the plates. For my setup I ended up using 2 shims on both sides. Getting the small pinion gear with it's dome washer into place was a real challenge. I probably took apart and re assembled the unit over 20 times. at best it is about 5 minutes and in the beginning >10 minutes to do this.

I dont really know what torque value I ended up with. I do know that I dont think I could have fit any more shims in and been able to assemble the unit.  The difficulty in measuring the torque is no practical way to fit a torque wrench to the end of the axle shaft. There are splines on the end and I could not find a socket that would grab.  I suppose in order to do this one should cut the long end off an old axle shaft and then grind the end to fit a socket. BTW the axle is inserted into one side to help keep one side aligned as well as turn the gears.

There is a bolt hole in the end of the axle shaft and I did put a bolt in there, but I was concerned that I would snap it off if I increase the torque.  A 6mm bolt is only good for 7 ft/lbs and I was looking for 25 minimum.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: Rebuilding LSD clutch disks 6.9
« Reply #13 on: 29 January 2020, 02:22 PM »
Robert you are a braver man than me, I looked at the service manual on this jobby and just went WTF :o  My comfort level with a diff is to drain the oil and pray 8)
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: Rebuilding LSD clutch disks 6.9
« Reply #14 on: 29 January 2020, 03:25 PM »
The entire rear axle / subframe assy has been the most physically difficult thing I have ever worked on. Parts are expensive, special tools have to be made and many others purchased.
I don't think many tackle all this for those reasons. I do know that I found 2 major issues and several minor that I Fixed.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550