[Phyrexia]

Hello all!

The TIS indicates the existence of three different 188mm differentials: the 188K, the 188L, and the 188LW.

The 188K appears to be limited to four-cylinder cars and only the most deeply nerfed of the six-cylinder cars, the 323i, so I will only mention it briefly here in this sentence for the sake of completeness.

The 188L came in E46, E83, and E85 cars, and probably in a variety of other chassis. This designation seems to denote the the second-generation 188mm diff that Metric Mechanic and others reference. The TIS says the L means "Smooth running" and I am trying to find the likely german word that starts with an L that translates to that phrase.

The 188LW came in E90s. However, the TIS indicates N52-equipped E90s came with both the 188L and the 188LW. As far as I can tell from searching RealOEM, E90s and E90 LCIs share the same differential part numbers. Does anybody know what's up with that? The LW stands for "smooth running, optimized efficiency", again according to the TIS. I believe this is the third-gen 188mm differential referenced by Metric Mechanic, which would imply that it was available in MY 2004 cars and later.

I'm under the impression that E90s had new "low-friction" differentials. I think I read this on the forum somewhere. Is the 188LW the "low-friction" differential? Physically, what are the differences between the 188L and the 188LW? Are there internal differences? Or does this just reflect the change to lifetime lubicration?

I've bought a 3.64 from an E85. If I'm properly identifying the two diff types, then it's a 188L. The 188L case has a drain hole, but according to RealOEM, the 188LW case does not. I won't really know if there are other differences until I get my 3.23 out when I do the swap. If the only difference is that I've got a drain plug, then that's great. If I have a diff that with several points more drivetrain loss, then that's less great.

[johnmyster]

Below, taken from Mark Miller's BMW maintenance guide (v03.13, 2013, page 37). He goes on to say that as of 2013, the e90 units are less durable than prior generation due to plastic bearing cage failure. Likely, ball bearings are "lower friction" difference (vs roller) and perhaps a smaller (lower contact) pinion gear. I don't know enough about these to know if that bearing change is on the carrier or the pinion. I would think that either would be subject to enough axial thrust to warrant a tapered roller design. Please keep us informed...should I ever need to replace a rear end and want to swap for an older design.

"Now, with the E90 3 Series, we have a very small pinion gear, no drain plug, and an oil
capacity under 0.5 U.S. quarts. Moreover, and most incredibly, BMW did away with the
strong tapered roller bearing in favor of old fashioned ball bearings. Worse, they are
mounted in plastic bearing cages."

[Phyrexia]

Thank you, John! I clearly need to read all the way through Mark's guide; he emailed me the current version a month or so ago. I have the Z4 diff on my bench partially disassembled for seal replacement. It definitely has roller bearings and a drain plug.

I'll be sure to document my findings.

Originally Posted by johnmyster

Below, taken from Mark Miller's BMW maintenance guide (v03.13, 2013, page 37). He goes on to say that as of 2013, the e90 units are less durable than prior generation due to plastic bearing cage failure. Likely, ball bearings are "lower friction" difference (vs roller) and perhaps a smaller (lower contact) pinion gear. I don't know enough about these to know if that bearing change is on the carrier or the pinion. I would think that either would be subject to enough axial thrust to warrant a tapered roller design. Please keep us informed...should I ever need to replace a rear end and want to swap for an older design.

"Now, with the E90 3 Series, we have a very small pinion gear, no drain plug, and an oil
capacity under 0.5 U.S. quarts. Moreover, and most incredibly, BMW did away with the
strong tapered roller bearing in favor of old fashioned ball bearings. Worse, they are
mounted in plastic bearing cages."

[atmosphericM]

So to clarify, one diff results in less drive-rain loss, but is potentially less reliable?
Please keep us updated man. I plan on doing the differential swap soon, and it's sounding like there might be better options than the other 3er diffs.

[Phyrexia]

Originally Posted by atmosphericM

one diff results in less drive-rain loss, but is potentially less reliable?

That's what I'm picking up from what he's putting down. I will need to verify that my stock '11 differential has plastic bearing cages and ball bearings. I think once I get the output seals pulled out I should be able to see the entirety of the bearing assembly.

The fact that you can drain the oil without pulling the rear cover on the older style diffs is nice. If indeed the only frictional differences are ball-bearings vs roller bearings then...as I understand it all, the older styles would be the way to go.

[johnmyster]

It appears that the pinion has double row ball bearings on the pinion, and single row ball bearings on the carrier. Plastic retainers on all. I remember enough of my mechanical design classes to know that ball bearings have substantially lower life than roller bearings, as the smaller contact patch leads to fatigue of the ball and races.

https://www.bearingkits.co.uk/BMW-E9...IR-KIT/899.htm

The voodoo seems to be in finding other BMW chassis that use the same differential casing as the e90. Does the 330/335 use different mounting points or driveshaft flanges from the 328?

Originally Posted by atmosphericM

So to clarify, one diff results in less drive-rain loss, but is potentially less reliable?
Please keep us updated man. I plan on doing the differential swap soon, and it's sounding like there might be better options than the other 3er diffs.

I think the loss difference would be pretty small in the grand scheme. I don't see a trend of failure threads on this forum, but I wouldn't expect Mark to comment if it weren't true. Perhaps historically BMW diff units were bulletproof.

[Phyrexia]

Well, this was a sweaty lesson learned, but the second gen 188mm E85 Z4 diff ( 33107514198 ) does not fit.

All of the parts here http://www.realoem.com/bmw/enUS/show...diagId=33_1142 are the same as their E90 LCI counterparts, except the actual differential. The actual casing of the 3rd gen diff is different than the 2nd gen.

The forward mounting points are spaced more closely on the Z4 diff. The body of the E85 diff is 1cm shorter than the E90 diff. I suppose the larger bushing could be pushed out 8mm or something and it would make up for it, but the front mount spacing seems to be a dealbreaker.

The 3rd gen diff does have ball bearings as expected.

[hassmaschine]

Originally Posted by johnmyster

I think the loss difference would be pretty small in the grand scheme. I don't see a trend of failure threads on this forum, but I wouldn't expect Mark to comment if it weren't true. Perhaps historically BMW diff units were bulletproof.

Yeah, they were. people were putting 500+hp through used '80s BMW 188mm diffs, which usually had at least 100,000 miles on them (often double that). The 210mm were even stronger.

I can only recall a handful of failures, usually guys who did a lot of drag racing or welded the diff so they could drift with 120hp. They should last 300k+ miles without issue.

It's not surprising BMW would cheap out. plastic cages and ball bearings? ugh. Best not crank up the boost on a modern turbo BMW..

[desertman123]

Originally Posted by hassmaschine

It's not surprising BMW would cheap out. plastic cages and ball bearings? ugh. Best not crank up the boost on a modern turbo BMW..

Don't worry, the keyless timing chain sprocket will slip and jump time before your diff blows

[tlow98]

I understand the cheapening of the design is a bummer, but is it actually resulting in failures?

I don't think I've even heard of an N52 rear diff going bad...even with 100k mile fluid changes.

[Phyrexia]

Originally Posted by tlow98

I understand the cheapening of the design is a bummer, but is it actually resulting in failures?

I don't think I've even heard of an N52 rear diff going bad...even with 100k mile fluid changes.

That's a fair point, and I don't know, though the design itself is not as old as the 2nd gen diffs and so it may end up being several more years before failures are seen?

I wish it had a drain plug. Hmmm maybe I'll make one myself

[hassmaschine]

Originally Posted by tlow98

I understand the cheapening of the design is a bummer, but is it actually resulting in failures?

I don't think I've even heard of an N52 rear diff going bad...even with 100k mile fluid changes.

these cars havent been around that long. There are E30s out there with 500,000 miles on the original diffs. The new ones are definitely made with lower quality, cheaper designs, so it seems unlikely they will be that robust.