Encouraging rear axle gear swap news.

[Shvegel]

I bought a 3.27 rear axle on eBay for my car and when I received it I looked at that greasy pile and my already perfectly restored 3.92 rear axle and decided that I wanted to swap the 3.27 gears into my original built with the car housing.  No housing to paint, no holes to plug and no vent to relocate.  The problem was after some research I found out that due to the odd nature of our axles coventional tools for measuring pinion depth and backlash don’t work and factory tools are few and far between.  After some thought I realized that you didn’t really need to find the depth of the housing etc the way you would need for an installation of new gears but (assuming a factory setup) only the current distance between the center of the side bearing race and the pinion crown so you could math that to the new installation.   I headed down to my lathe and built some tools.  I ended up making a stepped cone that centers on the side bearing race and a tool to measure backlash.  I then measured the 3.27 pinion depth and zeroed the dial indicator ( or in this case a digital indicator which I used for demonstation purposes).  After removing the pinion, changing bearings and installing the 3.27 pinion gear into my 3.92 axle with the same adjusting shim that was in the 3.27 housing I set the bearing preload and again measured the pinion to center of the side race.  The result was that the 3.27 pinion was .02 mm closer to the center of the side bearing race.   Since .02 mm is within the tolerance range I left it as it is.  Backlash also matched at .22mm which is high of spec by .06 mm but since the gears looked pristine and happy at .22 I left them there. 

What all this means is you may be able to swap bearings in your rear axles without measuring as we found when I did a bunch of differentials for Saab as long as you retain the original adjustment shims.  I am going to do a straight bearing swap on a 3.69 axle in February( when I am home next) that I have to be able to verify what I think to be correct and I will let you know how it turns out.

Getting back to the digital indicator for a second I wanted to say that they should be avoided in situations like this where if you lose the measurement you locked in you are really up a creek.  Batteries die, buttons get pushed and you think that you are just going to lay it carefully on a bench and pick it up an hour later and you get the wrong bearing or seal and it ends up being days instead of minutes.  Use a regular "Dial indicator" for your own sake.

[dakman29]

Not sure I fully understand your post, not due to its contents but to my limited knowledge base. Here is a link to an ebay auction for a  3.28 ring and pinion:  https://www.ebay.com/itm/Ring-and-Pinion-gears-Early-style-Drum-brakes-3-28-gear-ratio-for-W113-W111/222667570589?fits=Make%3AMercedes-Benz&hash=item33d8057d9d:g:XpUAAOSwKfVXF5tj&vxp=mtr

Are you saying in your post that these can be installed in the existing differential housing without replacing the entire rear end with the same positive results as a full on swap?  Thanks

[clunker]

@Shvegel: This is interesting - were your expectations from the measurements validated when checked using gear-marking compound/contact patterns?
The implication is that the housing itself can be assumed to be a reliable reference locator between all W113s/W108s/etc, and that the shimming on a, properly set up, other housing/pinion/ring can reliably carry over.

[Shvegel]

Dakman 29,  Unfortunately no.  With the 3.27 gears that I removed from another housing I was able to measure the distance between the top of the pinion (crown) and the centerline of the axle side bearing of the original(what appear to be original bearings, original seals, bolts not deformed paint not broken) setup and simply replicate it in the new housing.  Setting up new gears is a different animal since you have to be able to reliably measure between the center of the side bearing and the pinion crown reliably which is much more difficult.  Going out on a limb what you could do is measure the original setup as I did zeroing the indicator then correcting the measurement for 2 factors.  The first is the fact that the 3.27 pinions are 2 mm taller than either the 3.92 or 4.10 which all things being equal would mean that the indicator would read +2mm with the new gears.  The second would be to allow for the adjustment in depth that is etched into the pinion crown at the factory.  When gears are made they are run on a fixture or “Dyno” and the pinion depth is adjusted until the gears are at their quietest.  This adjustment is the recorded on the pinion crown.  What you will see when you look at the crown is a usually 4 digit number that matches one stamped on the ring gear that denotes a matched pair of gears and a second number that is the above mentioned correction from the dyno run.  In my case the 3.27 gears were marked “+11” which means they wanted the pinion to be .11mm furthur away from the centerline of the side bearing.  On the original 3.92 gears the markings were +44 or .44mm furthur away from the centerline of the side bearing so assuming the original pinion was set up correctly I should see +2.33mm on my dial indicator meaning that the top of the new thicker 3.27 pinion should be 2.33mm closer to the side bearing centerline.

Clunker,  yes I did do a marking grease run but forgot to photograph the results.  The pattern was very nice on both the drive and coast sides. I am not ready to say we can count on the housings being standard but it is encouraging that 2 different housings of 2 different sizes (the 3.27 housing is slightly larger) appear to measure near identically.  I originally wanted to buy the eBay gears from Babek but was daunted by how I would set them up so I didn’t buy them.  I then came across a 3.27 rear that was far cheaper and I realized that replacing gears from a know starting point was far easier than starting from scratch.

[Shvegel]

Dakman29, I remember now why I was concerned about the eBay gears.  They don’t appear to be factory Mercedes gears.  I would expect Mercedes gears to adhere to their specification of exactly 2mm taller on the pinion.  The eBay gears are unfortunately an unknown in terms of quality control.  I guess you could use a tool like mine and set them up but you might spend a lot of time and money fiddling with them to get them dialed in correctly.

[450sl]

Shvegel ,
How do you deal with a somewhat ''crushed''  spacersleeve due to former overtightening of the pinion grooved nut ?
i think the bbb says to check friction after tightening the nut ; feels a bit dodgy method to me.
mark

[clunker]

Thanks for this analysis and all the detail. I am going to swap my whole intact axle from 4.1 for 3.27 - your post had me considering opening the 3.27 but I am not sure it would end well, and anyway my existing 4.10 is hardly pristine!

Apologies if I am nitpicking or wrong, but as per you valuable post in the General forum which had the MB axle specs table, I see the 3.27 has pinion head to ring center of 67.5mm vs 66mm for the 4.10 - I assume that implies that the 3.27 pinions are 1.5mm taller than the 4.10 (as opposed to 2mm you posted, which I think from your table applies to the 2.82 only.)

[dakman29]

Thanks for the info Shvegel. Definitely beyond my capabilities. If I make the change it will be for the complete axle.

[Shvegel]

clunker,
Not nitpicking at all.  I missread the instructions and you are correct the 3.27 is 1.5mm taller and the 2.82(never seen one) is 2mm taller.  I went back in my photos and verified that as well. 

[Shvegel]

450SL,  the crush sleeve is essentially the meat in a bearing sandwich. The concept being that the you simply crush the sleeve down until you get the proper preload and then lock the pinion nut and everything is stable and locked.  Unfortunately, if you overtighten the pinion nut to the point that the pinion preload is too high the only correct way to fix it is to dissasemble the rear axle and replace the sleeve with a new one.  The crush sleeve sandwich is what locks the inner bearings to the pinion shaft. I wouldn’t worry about the rear bearing as it is a hard press fit but the forward one is a fairly light fit.  My worry is that without the proper crush on the sleeve the forward pinion bearing might spin on the pinion shaft ruining the pinion gear.

  I am out of town at the moment but
will be home in a couple days.   I have a housing and pinion on my bench.  Let me see if I can figure out a way to get ahold of the bearing well enough to pull it out. I don’t think it is possible but I will try.

 It is very easy to overtighten the pinion so I always keep a few crush sleeves around.  They are only a few dollars each and you don’t have to stop and order another. You are correct that the pinion bearing preload(turning torque) is set after the nut has been tightened.

[450sl]

Shvegel, there are some special mb tools for disassembly of these bearings ; will look for it in documents.

[450sl]

from bbb

[mercakungen]

Hello,

I am doing gear swap on my rear axle. On the original (3,92) pinion was marked "+39". I thought that the pinion depth should be 66,39. That would be logical but not with Mercedes... Mercedes does it opposite way. The right pinion depth is 65,61 and that was it by measuring.  The Mercedes specialist who sold me genuine MB 3,46 gears confirm that.

On the other topic was an table about bearing preloads. The table was a quite difficult to read due to it´s small size. I´m not sure if there was cmkg instead of cmkp? The German table I have says cmkp (1cmkp = 0,1Nm).

BR,
Matti

[mercakungen]

cmkp and cmkg are the same...

[MikeSimon]

Quite a while ago, the guys in charge of the metric system decided that kg would only be used for weight, whereas the unite for force should be kp (kilopond).
9.81N (Newton) equal 1 kp.
1kpcm (1/100th of a kpm) equal roughly 0.1 Nm

[mercakungen]

Hello,

Job done. As I mentioned before I started by measuring the depth of the original 3,92 pinion. The result was 65,61 mm. By adding 0,39 mm (+39 marked on the pinion head) gives 66,00 mm.

Next I installed the 3,46 pinion without shim. I set the bearing  preload to 5 cmkp. The pinion depth was 67,55 mm. 67,55 - 65,92 (+8 marked on the pinion head) = 1,63. I don´t know how this is possible but thickness of the original shim was just that 1,63! So I installed the new pinion with original shim and set the preload again to 5 cmkp. I checked the pinion depth again and it was 65,92 mm.

I decided to go with original shim on the side bearing too. I started with 1 mm feeler gauges between axle half and housing.The back lash was enormous so I switched to 0,5 mm feeler gauges. Still too much play and I took all away. By setting the preload to 7 cmkp the back lash was 0,15 mm. I checked the pattern and it looks pretty much same as it was from the factory (the brand new gear set still had gear marking paint when I opened the package).

I´ll post some photos of my methods on my project topic.

BR,
Matti

[ja17]

Very good Matti, looking forward to seeing the photos!