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      06-01-2020, 03:56 PM   #1
L_Azevedo
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BMW E46 differential

Hi! I am new here in this forum and i don't own a bmw (yet) , but i am a huge bmw enthusiast, so much that i decided to do an essay about the bmw e46 open differential for my class of mechanic technology. Getting an e46 differential was easy, i found one in a junkyard, but there's not much information about these things on the internet.
Can someone help me with this essay ? I want to know if this differential has any problems related to wearing or some flaw in the design of the gears.
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      06-01-2020, 04:15 PM   #2
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i had E46 M3 for few years and didnt have much problem except a little knocking right before putting into gear when its too hot.. other than that it was totally ok.. general complaints are LSD does a little graining on low speed tight corners which in level it never had my attention.. open versions didnt even have that of course.. generally its not a problematic diff..
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      06-01-2020, 04:41 PM   #3
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Quote:
Originally Posted by L_Azevedo View Post
Can someone help me with this essay ? I want to know if this differential has any problems related to wearing or some flaw in the design of the gears.
The only diff that has a somewhat weak spot is the e46 m3/z4m diff (but that's not an open diff, it's an LSD with a speeddependant oilpump/piston action)
That diff can develop an input shaft seal oil leak.
The s54 engine is a high revving engine, and the rear diff on the e46/z4m has a high final drive ratio, so the input shaft of that diff makes more revolutions per driven kilometer, thus it wears faster, mainly resulting in worn input shaft oil seals.

Further more there are 3 types/sizes of diff's fitted in the e46 chassis:
210 diff (only fitted to M3)
188 diff
168 diff

The numbers indicate the size of the crownwheel. The smaller engined cars got the 168 diff, the heavier engined cars got the 188 diff.
Except for the 210diff, the diffs also come in different ratio's

This is a (not complete) list:
http://www.bokchoys.com/differential/GearRatios.htm

You can see in the ETK which type of car got which diff, for examply by looking at what gasket/rear cover is listed:
318i got a 168 diff:
http://bmwfans.info/parts-catalog/E4...ve_gasket_set/
320i with m52 engine also got a 168 diff:
http://bmwfans.info/parts-catalog/E4...ve_gasket_set/
320d got a 188 diff:
http://bmwfans.info/parts-catalog/E4...ve_gasket_set/

The letter K after the 188/168 designation means 'Kurz" (german for "short"), probably a housing/fitting designation.

The 168/188k diffs out of the e46 differ from the earlier style bmw diffs, in that shimming the outputbearings of the diff (and the diff itself) is done by large circlips:
Here you can see 2 with their thickness laseretched in them:


For most of the adjustment on the 188k/168k diffs, you can look them up in the section for e36 cars; back in those days BMW fully supported diff rebuilds&parts. And as virtually all gears etc are the same for that car, you can use those specs.
For instance, backlash for a 188k diff is 0,06mm - 0,14mm
In the e36 section of TIS are also specs for preloading the bearings (mainly input shaft bearings), and some interesting pictures of what specialty tool to use for measuring that. A very sensitive torque wrench (click style) won't work as you have to measure drag forces.
This is an online version of TIS (technical information system); If you want to know how BMW's work (technically); learn how to use it.
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Last edited by GuidoK; 06-01-2020 at 04:57 PM..
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      06-01-2020, 04:45 PM   #4
L_Azevedo
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I forgot to mention that itīs the medium size differential that has the 188 mm ring gear. But i didn't know the meaning of the letter K so thank you.
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      06-01-2020, 05:05 PM   #5
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I don't know if you've already taken your diff apart, but like I said, you need a very large size circlip pliers:


For the 188k diff, it usually first starts wearing at the output bearings. But usually they last at least 300k km, so it's not really a weak spot/design flaw with those numbers.

Interesting fact is that very late style 188k come without a drain plug. (only a fill plug).
But I don't think they've been fitted to e46 cars (mainly facelift Z4's and probably also X3's (these share the same rear axle; e85 z4 is virtually the same car but made into a roadster)

Also the 188k diff's have at least 2 different cores: one for ratio's 3,07 and lower, and one for ratio's 3,15 and above. I don't know if the diesels have yet another core (very low ratio's, for example 2,47)
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Last edited by GuidoK; 06-01-2020 at 05:12 PM..
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