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12-19-2023, 09:42 AM | #1 |
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Drives: 128i 6M, 1UZ S13, '62 C10
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3.46 Differential Swap into Manual 128i?
Gear swaps are a wonderful way to really wake up a "slow" car. I've been very enticed by the 3.73 swap that so many rave about. However, I have an arthritic left knee and I do a decent amount of highway driving, so I have been stubbornly searching for something in between the tall 3.23 stock gearing and the 3.73 E90 auto gears for my 2010 128i 6mt.
Using 225/45/17 tires, 0.85 sixth gear ratio, here are the given RPMs at 75mph: 3.23 - 2694 rpm 3.73 - 3111 rpm I've noticed some models of earlier Z4s (E85/86) have 3.46 gearing. This is smack dab in the middle. 3.46 - 2886 rpm Looking at ebay listings, damn it sure looks like the same case as mine. I'm really tempted to try one out, it seems like I would just swap my rear cover over, refresh it with some new seals, and be good to go. Am I drunk? Second question - Which diff case does the manual 128i come with? 188L? 188LW? 188K? Here's some links I found helpful in my searches, for anyone else's reference. Factory gearing and application table: https://www.moreheadspeedworks.com/bmw_gear_ratios/ Diff Case info: https://www.difflab.com.au/pages/bmw-differential-types - **Note the typo of 168LW on this page, I believe it is meant to say 188LW Internals application reference: http://www.wavetrac.net/application.htm Last edited by cerealwars; 12-19-2023 at 12:12 PM.. |
12-19-2023, 12:18 PM | #2 |
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Alright, well I found some more detailed ebay listing pictures and it seems the Z4 housing is in fact a bit different. The front mounting points are narrower than on the 1er, and the rest of a the casting is a bit different too. So, probably a no-go on the Z rear end and I'll just have to go for the 3.73s, or if I'm lucky maybe I can find a 3.63 out of an E90 330i, since I heard that also works. I'll try and update this thread if I happen to find something useful.
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12-20-2023, 11:29 AM | #3 |
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This topic is quite interesting and on time for my next steps,
I am looking to get an LSD for my 128i and checked the options that diffsonline provide for the 128i and I only saw the oem 3.23m the 3.64 and 3.73, there are some other crazy options like 4.1 or 4.44 but those would be just way too much. I currently have the 3.73 in my manual 128i and I really like it, even in highway is really not bad to cruise at 75 at a little over 3k rpm. However I would consider the 3.64 if I decide to go with a diffsonline unit it just depends on the budget to continue the project next year. now that you mentioned that the 330i diff works, I might try to find a 330i 3.64 diff on ebay, buy a wavetrack lsd and put it together myself, the units that diffsonline offer are sweet but pricey I think we are pretty close if you want to try out a manual 128i with the 3.73 just let me know |
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12-20-2023, 06:50 PM | #4 | ||
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Drives: 128i 6M, 1UZ S13, '62 C10
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Quote:
Doesn't quite seem worth it for me right now, I'd just go with the 3.73s and know that the thing is set up right. I've set up a more than a few diffs on my old 240, but not sure if it's worth the gamble on my "reliable adult car". I'm becoming older and "sensible". Time to put me down I guess. Next step would be to verify the pinion gears themselves have the same spline dealio for the flange to swap over, before dropping cash on a unit that won't work. Realoem would be helpful here, maybe I'll look at the interchange tomorrow just for shiggles. An alternate route, if you're desperate enough: You could use any diff above if you also snagged the companion driveshaft. Then you would then have to take both driveshafts to have a driveshaft shop frankenstein them for a few hundred bucks. Quote:
Last edited by cerealwars; 12-20-2023 at 06:57 PM.. |
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