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 rear axle rebuild: torque values for bearings?
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Gael

771 Posts

Posted - 03/02/2010 :  06:00:21  Show Profile  Reply with Quote
Hi all,

I am rebuilding my W111 3.27 LSD rear axle. I have finished the limited slip differential and got the races out of the center housing. I am now going to put everything back together with new bearings and races.

My question is about the torque to be applied to the input flange bolt and the big side toothed bolt for the bearings to work under the proper tension. Does anyone know these values? Or is there a rule of thumb ala front wheel bearings i.e. torque to max and then undo by 90?

I'm planning to do the adjustment first for the side bearings without the pinion, and then for the pinion without the diff. How freely should these elements be turning? Should I feel some resistance?

Chris Johnson

USA
3751 Posts

Posted - 03/02/2010 :  11:39:54  Show Profile  Reply with Quote
The proper torque is determined by measuring the torque required to turn the bearings themselves.

For example, the entire pinion assembly must be installed in the diff housing, and, with the pinion depth already set correctly and a new collapsible spacer installed, the turning torque of the pinion shaft in the bearings is measured. This value will be in the "inch-pounds" range.

The torque on the nut on the pinion shaft is increased until the turning torque of the shaft in the bearings reaches the correct range. The (new) collapsible spacer will require that the torque on the pinion nut be somewhere around 150 foot-pounds in order to achieve a shaft turning torque in the proper inch-pound range.

Once the pinion shaft is adjusted to the proper turning torque, THEN the ring gear carrier assembly bearings are adjusted with the big slotted nut on the side by measuring the COMBINED turning torque of the pinion gear and carrier assembly (also in the inch-pound range) WITHOUT the axle shafts or homokenetic joint installed. This is still measured at the pinion shaft nut.

If new pinion and carrier bearings are installed, then the turning torques should be set to the high side of the allowable range. If used bearings are installed then the turning torques should be set to the middle of the range.

Once the rear axle is fully assembled (without brakes)and with the axle tubes straight out, the total turning torque (including axles and wheel bearings) should be measured and compared to the assembly specification for confirmation that everything is okay.

The appropriate "torque wrench" to measure the small turning torque values can probably be found at a good shop supply house. Mine is a unit called "Micro-Torque" made by MHH Engineering in England. I bought this tool more than 20 years ago though, and it cost nearly $200 then. It has a range of 0 - 50 inch-pounds.

This particular tool has a quarter-inch hex socket end, and I epoxied a quarter-inch hex. bit into the rachet end of a half-inch drive socket extension. The extension fits into the special tool for the pinion nut, and this allows easy checking of the turning torque at the pinion shaft nut.

This entire process is detailed in the service manual. Neil at Star Motors says that it is this correct setup and adjustment of these bearings that allows the 6.3 axle to be reliable and not break teeth off the gears even when operated very aggressively. Towards that end, there is no substitute for getting it right.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Gael

771 Posts

Posted - 03/02/2010 :  12:48:49  Show Profile  Reply with Quote
Thank you Chris for this very detailed procedure. My w/shop manual only gives a torque value for the complete rear axle drive (20-25cmkp) but not for each step (pinion, pinion + diff without shafts). Would you have these values? I'm going to look for that measuring tool.
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Chris Johnson

USA
3751 Posts

Posted - 03/02/2010 :  13:19:20  Show Profile  Reply with Quote
According to the '72 Technical Data book (thanks Charlie!) the pinion shaft turning torque with new bearings is 16-18 kpcm and 5-10 kpcm with used bearings. Both numbers assume a new collapsible spacer is installed.

The increase in turning torque when also measuring the carrier bearings is 7-8 kpcm.

This book says that the total turning torque, with axles and wheel bearings installed (and axles level), on a USED rear axle (used bearings), should be 26-30 kpcm. It does not have a total value for NEW bearings, but based on the individual torque values, I would expect this to be in the range of 36-40 kpcm.

This book has specs ONLY for a 3.27 axle from a 108 or 109 chassis car. If the axle is from a different car, then these numbers should be confirmed before assuming they are correct.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
100.012-12-000790
100.012-12-000867
www.300SE.org

Edited by - Chris Johnson on 03/02/2010 13:26:22
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Gael

771 Posts

Posted - 03/02/2010 :  15:23:39  Show Profile  Reply with Quote
Thanks Chris, this is very useful! My axle happens to be a 3.27.
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bwostosh

USA
485 Posts

Posted - 03/02/2010 :  16:42:51  Show Profile  Visit bwostosh's Homepage  Reply with Quote
Chris,
Is "26-30 kpcm" equal to kilopond centimeter?
and thus....
28 kilogram centimeter = 2.0252438729 pound foot?
That is not much resistance,
but enough to get to zero at temperature.
Thanks for the spec.


Brian O.
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Gael

771 Posts

Posted - 03/02/2010 :  19:08:35  Show Profile  Reply with Quote
I've been looking around for that torque measuring tool without much success so far. But I measured the distance between the center of the input flange and the center of one of the four peripheral holes and it is 4.1 cm. If I remember well my highschool, torque is a weight multiplied by the distance to the center it is applied to. So, if I hang a bottle of one gallon of milk to one of these peripheral holes when it is at 3 o'clock, I may well have a value comprised between 16 and 18 kpcm, right? I may go on adding around half a gallon to get the additional 7-8 kpcm with the diff in place and two gallons and a half (and a few sausages) total with the shafts in place. Does that sound a good approach?
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Gael

771 Posts

Posted - 03/02/2010 :  19:25:42  Show Profile  Reply with Quote
A refined version would be to roll a rope on the space just behind the flange. This is to avoid the value to change as soon as the flage rotates from the 3 o'clock position. Radius there is 2.45 cm so I would have to hang a weight of 7 kg to get a value comprised between 16 and 18 kpcm. A bag of oranges may well do the trick...
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Chris Johnson

USA
3751 Posts

Posted - 03/02/2010 :  19:45:12  Show Profile  Reply with Quote
Gael, I found some modern equivalents here:

http://www.mountztorque.com/products/torque-screwdrivers/microtorque

Brian, your math is correct. For our non-metric friends, kpcm to ft-lbs. = ((kgcm/100)*7.233). Note that one kpcm = 0.07233 ft-lbs., or 0.868 inch-pound, so it requires not only a small, but very accurate gauge to tell when things like the carrier bearings are properly adjusted (the range being 7 to 8 kpcm). I do think it would be possible to do some interpolation to get the bearing load set correctly if the torque wrench didn't have settings at quite that high a resolution.

Gael, I am going to assume that milk weighs about 8 pounds per gallon (it probably depends on if it is whole milk or a low-fat version). A "length" of 41mm/25.4mm per inch = 1.614 inches. This times 8 pounds = ~12.9 inch-pounds. That, divided by 12, equals 1.076 foot-pounds. The desired torque is 17 kpcm = 1.23 foot-pounds, so, by itself, the milk may be a little light. I think you may have to include part of a sausage even in the pinion torque calculation.


Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
100.012-12-000790
100.012-12-000867
www.300SE.org

Edited by - Chris Johnson on 03/02/2010 19:47:43
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Gael

771 Posts

Posted - 03/02/2010 :  19:58:43  Show Profile  Reply with Quote
That's because you didn't include the weight of the bottle!

More seriously, assuming milk is as heavy as water (if not I can replace it by water) 3.9L is 8.7 pounds. Plus the weight of the plastic container and I should reach over 1.2 foot pounds...
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Art Love

Australia
6231 Posts

Posted - 03/03/2010 :  05:12:19  Show Profile  Reply with Quote
I thought I'd moved to a cooking website for a minute.
Art
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Ron B

Australia
11619 Posts

Posted - 03/03/2010 :  19:28:03  Show Profile  Visit Ron B's Homepage  Reply with Quote
The French have a way of bring food into everything...

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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Gael

771 Posts

Posted - 03/03/2010 :  19:35:13  Show Profile  Reply with Quote
Wait! Wine is on its way!
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