3.06 ATB Differential
 

After recently winning the bid on a Quaife QDF5V ATB differential, I broke my 3.06 open diff down in preparation. This will be going into my 90 300CE, which currently has 3.27 gears. The donor 3.06 is from my 91 CE parts car. The Quaife is currently being shipped so as progress happens on the diff I'll post pics and update the post.


The breakdown is pretty straightforward. I'm not messing with the pinion other than to replace the seal so back cover off, clips out and hubs out. Unbolt and remove the side bearing carriers and the open differential falls out. After the bolts are out the ring gear, a little heat applied and the ring falls right off.

I'm a bit nervous about setup in that special shims are used to set the carrier in position. Most of these shims are NLA from Mercedes so anybody with spares give a shout out. I've got 1.13mm and 1.93mm and in a perfect world they would get the job done. I'm planning to replace the side bearings. They're not cheap but without the special tool to pull them it doesn't seem worth the effort. So considering it will have new bearings and a carrier manufactured by a 3rd party, it will be a miracle if my original shims get it setup right.


Here's the beast stripped down:

Despite tracking showing a sorting error, the differential arrived a day early. :eek: It's a nice unit but for the outlay expectations are high. Not disappointed.

Side bearings are on order but are still a couple days out. Setup doesn't begin until they're in and pressed on. Circlips to retain the hubs arrived today as well. As advised the hubs will need a slight trim on the lathe to give the circlips enough depth to work in.

Ain't she pretty?

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I have to go to work now but I will try to get back to this tonight. I may be able to help with shims and side bearings.

If this is a 210mm diff I have 6 sizes of side case shims.

1.526
1.202
1.863
1.908
1.490
1.509

I guess what you are calling the hubs are what I call the axle flanges. I also have 6 sizes of axle flange rings. No need to put your axle flanges on the lathe. These rings are also selectable and I have 6.

3.072
2.928
2.797
3.110
3.103
3.019

No sense in getting MB side bearings as they use standard Timken available everywhere. You will probably have to buy the race and cups separately.

As far as removing side cover bearings the OTC puller 4534 will do the job with a few minor modifications.

I had to make a new center ring with studs to pull the jaws in closer or spread them out in the case of the outer races. See the first post in my differential tool build ideas showing this puller being used to pull the races out of the side covers.

Let me know if you need anything I can work something out.

The bearings came in today and I got them pressed on. This amount of progress allowed me the first opportunity to measure for setup beginning with case spread. The spec is to have .15-.20mm of spread. This is essentially the preload on the side bearings. I stuck my original shims on the side bearing carriers and torqued them into the case. Instead of .15mm preload, I had .15mm clearance. I managed to score another two shims from a junk diff, one of which is 1.0mm and swapping that one for my 1.15mm got the preload to 0.0mm. If I can locate another shim in the 1.8 to 1.85 range I can get the preload set and then add the ring gear to the mix. Hopefully backlash ends up ok after splitting the difference in preload between sides.

Looks like you were typing while I was typing.


I went ahead and ordered the bearings from Mercedes. They weren't exactly cheap but rather than hope I cross referenced them right I bit the bullet.


I'm very interested in the 1.8xx shim though once I mount the ring gear my backlash could be way the hell out. I could still be futzing around to find a combo of shims that measure 2.8xxmm collectively that gets the ring where it needs to be. At least I know what backlash needs to be. The number is stamped on the pinion gear. Mine says .12 and I measured .13

The lathe work for the hubs is just to deepen the groove that the original retaining circlip held. The groove gets cut a little deeper allowing later model captured circlips to be installed. As it stands the replacement circlips sit a bit proud of the root of the splines and they need enough room to compress under that dimension.

Once you get the preload correct with some amount of backlash at that point the total thickness of shims remains the same and it becomes a mater of decreasing thickness on one side and increasing by the same amount on the other. Yes you need an unlimited supply of shims and a surface grinder is a huge help.

Well, after J. Roncallo shipped me his collection of shims I went ahead and bolted the ring gear to the carrier. With it installed the closest shim combinations were tried. As luck would have it, my closest combinations were either too loose or too tight. 1.8 and .95 mm shim combo doesn't quite hit the spread spec and ends up .21 backlash. Next closest is 1.45 and 1.3mm and they end up in the negative backlash range and pretty much bind the assembly. If I could locate a 1.7 to use in place of the 1.8 it likely will be golden. The search is on. There are a couple shops local that may have a pile of old diffs around. Worst case scenario I'll have to get one of the thicker shims ground.

There is a highly respected old timer in the Benz world that has a small shop nearby so I rang him up today. Turns out he had a significant collection of shims and was gracious enough to let me leave with the lot of them. A bunch of measuring, disassembling, re-measuring and disassembling again has yielded what I believe to be a well set up differential. I ended up with a 1.6 mm and a 1.1 mm shim to get 0.2 mm case spread and 0.11 mm backlash. The case spread is the tight side of the spec but considering I have new bearings I was hoping to hit the tight side. The backlash spec for this matched ring and pinion is 0.12 mm, but I feel ok with 0.11 mm.

The old timer offered to double check my setup with the rarer than hens teeth official Merecedes differential setup tools when I return the shims. Hopefully his numbers match mine as even in his collection, there were no 1.65 or 1.7 mm shims.

Actually, the +.12 that is etched into the face of the pinion is the variance from the "zero" position, and is used in computing the thickness of the shim that adjusts the pinion depth.
The good news is that by chance ".12" is within the range of .08-.14mm that is called out for the backlash, and so, in this case did not cause an error.

Good catch, I just glanced over most of the pinion stuff in the service manual. I feel even better about that 0.11 now.

Good to see you got it doing finding a guy like that with a stash of shims is a big help.

PM me the old timers name. I started working on Benz's in the late 70's in Denver maybe its my old boss.

I had the chance today to have the setup doublechecked with the official setup tools today. Where I had previously measured 0.11mm backlash, it was a bit tighter, 0.08mm to be exact. The spec is 0.08 to 0.14 so I'm really glad I had the opportunity to have it double checked. Had it been any tighter I'd still have thought it ok. The rotational torque was also measured and it too came in on the tight side but still in spec. With everything measuring up I went ahead and installed the seals and buttoned it back together.

Actual installation will be a while yet. I'm planning to do a complete subframe swap and not just a diff swap. I have a V8 subframe and matching back cover for the diff. The V8 subframe has larger diff mounting bushings that are spaced farther apart than the 6 cyl variant. I also think my current subframe may be tweaked. The right rear camber is a bit high and there is a some of bodywork in that corner. So it's gonna be a multiple birds / one stone kind of thing.

What made you decide to go to a 3.06 over keeping the original 3.27.

I'm currently running the 2.47 had a 2.65 in my M120 560.

Fuel mileage performance was pretty profound increase with the 2.47. But it does feel like its dragging a boat anchor after driving it with the 2.65. And it did loose about 1/2 sec in the 1/4 mile despite being an LSD differential, where as the 2.65 had a spring loaded phantom grip and still spun one wheel. The numbers below I actually find a bit unbelievable, so I want to do more testing before I swap in a 2.82.

Greensboro NC to Athens GA 297 miles, 12.539 gal, 23.7 mpg, average speed ~ 72 MPH, top down.

Athens GA to Atlanta GA 211 miles, 13.504 gal, 15.6 mpg, average speed, first half ~ 60mph top down, second half ~90mph top up.

Atlanta GA to Summerfield NC 331 miles, 13.072 gal, 25.3 mpg, average speed ~ 72 mph, top mostly up.