In reply to docwyte :
Yeah, I also went ahead and ordered a Wavetrac LSD to go with it recently. Having an inexpensive pumpkin in the garage to swap the LSD into will allow me to take me time and hopefully not mess anything up too bad.
I also ordered new axle gaskets, sealant, Redline fluid, etc. Overall, including the cost of the 3.73 diff, it's around $1600, assuming you don't count the money I spent on a few new tools that should help with the swap (those never count, right?). Going down this path, it'll cost me roughly half of what I would have spent via Diffsonline.
Well, well, well... would you look at what the UPS guy dropped off yesterday...
In order to move forward with this project, I had to upgrade to a slightly larger vice to hold the diff in place...
I've been meaning to pick up a larger vice for quite a while now. This project finally gave me a good reason to pull the trigger.
I plan on cleaning up the differential housing and making it look mildly pretty before I swap the Wavetrac LSD into it.
Today I tore apart the diff and installed the Wavetrac LSD. It took me about 4.5 hours. Technically I still need to install the axle seals and the diff cover, but those should be fairly easy things to do, that should only take a few minutes.
Murphy's Law kicked in today. Just about everything that could be a headache, was a headache.
I previously purchased a tool to measure backlash... while trying to set it up to take a before measurement, it fell onto the concrete and was no longer responsive.
I found out that the axle seals are technically made of metal. They were damn near seized in the housing and took lots of pounding on a crow bar to get them out!
The spring clips/shims that hold the bearing in place are just difficult to remove (at least one side was). The only tool I had that seemed to help with a set of long-nose, 90 degree angle needle nose pliers.
I thought the bearings themselves would come out pretty easily. Oh how naive I was.
The races on the diff itself were seemingly not designed to be removed. In order to get them off, I have to use the combination of a bearing puller tool, along with a 3-jaw puller. Nothing else I tried seemed to move the race... the other side? I literally had to go to town with an angle grinder to create some room underneath the race in order to use the bearing puller tool.
While putting things back together, I thought the OEM ring gear would slide right on with a few whacks of a rubber mallet... nope. I destroyed a good portion of my rubber mallet getting the ring gear on, only to discover that the holes were absolutely perfectly lined up and I had to remove the ring gear and start again.
After everything went back in the casing, I had to re-fight with those damn spring clip/shims! The first one took a decent amount of effort, but the second one, the tolerances were so tight, it must have taken me ~20 minutes to get it fully seated.
I'll do a full write-up when everything is finished.
After spending a good portion of a day pulling the diff from a junkyard... then another portion of another day, cleaning and restoring the diff... then half of today ripping it apart and installing the LSD... I found myself thinking: perhaps I should have paid the extra money to just have the professionals at DiffsOnline build this thing for me. This is a legitimately substantial project that has been less than pleasurable. Which, to be fair, I don't really enjoy wrenching on cars these days, so that might be part of the equation.
EDIT: I actually installed the axle seals. I just had to make a trip to the store to pick up an 80/82mm oil filler cap wrench to use as a tapping tool, as nothing else in my toolbox was the same diameter as the axle seals.
I picked up a replacement backlash measuring/dial indicator tool. According to stats I've read on the Internet, BMW recommends setting backlash between .002" to .005". I managed to measure backlash at .003", so just about perfect! Good thing, as I didn't want to have to mess with testing a bunch of random shims!
EDIT: Knowing that the backlash was within spec, I went ahead and used some sealant in order to mate the diff cover to the housing. To say I lack "steady hands" or things like "precision" when applying sealant is an understatement.
Now I just plan on waiting ~24 hours for the sealant to cure before I fill her up with diff fluid. Then it's just a matter of finding the motivation to swap my fully assembled 3.73 LSD into the car.
Note to self: when you order, say, a LSD from a company, like say, Wavetrac, it's a good idea to read through the FAQs before you start ordering fluid for your shiny new diff.
When I was ordering everything I thought I would need, I ordered a couple of bottles of Redline 75w90, assuming it would do the trick. Which, technically, it will. However, since the Wavetrac LSD is a helical/gear type unit, they actually specify that you try to avoid using diff fluid that has any sort of friction modifier for a [clutch type] LSD. They specifically use the words:
You know, like the bottle of Redline 75w90 that specifically says "for hypoid limited-slip differentials". Would it probably be fine? Yeah, probably. But draining the diff once it's installed in the car is a real pain in the neck, so I would rather just use the proper gear oil in the first place.
As it turns out, for this exact reason, Wavetrac seems to specifically recommend Motul 300 gear oil (NOT designed for LSDs). Well, I suppose there's another $50 down the drain:
jgrewe
Dork
9/18/25 12:36 a.m.
I hope it isn't an issue but i'm pretty sure the snap ring gap is supposed to line up with the slot at the top bearing bore for oil to pass through.
If you have more drag than you think is OK when you hand spin the pinion, check the depth of the side seals. I had one not quite in far enough and it caused the diff to feel like it was going to drag the car to a stop.
In reply to jgrewe :
I think you might be right. I didn't take detailed photos of the snap rings during tear down, but looking back I believe the gap was inline with the top bearing bore hole. E36 M3.
I'm glad someone caught this before I installed the diff in the car. What's irritating is that I've watched several videos of assembly and there's a plethora of pertinent information that people leave out. Once the diff is in the car and I've gotten a bit of seat time to give impressions, I'll be making a thorough, detailed blog post to hopefully prepare others that plan on DIYing this job.
I just removed the axle seals (much easier the second time around!) and aligned the snap ring gap with the top bearing bore hole, which unfortunately means I now need to order more new axle seals. So much for swapping this thing into the car this weekend, as I'm back to waiting for parts in the mail.
This isn't the hardest job I've done on this car, but man, for whatever reason, it's been one of the most tedious and irritating. For some people that enjoy more detailed projects, I can see this not being a terrible job. For ole' Mongo over here? Me like get things done fast. Me no like so many steps and stupid details.
In reply to jgrewe :
Great catch. That's the kind of help I could use about every time I work on something!
docwyte
UltimaDork
9/18/25 8:41 a.m.
I'm pretty sure I've got the gear oil you need kicking around in my garage. If you want to come by and see, let me know...
I'm glad I wasn't too late noticing. It seems like here is very little concrete info on these diffs online. I had to combine info from the previous 188 diff with my general knowledge base of diffs to do my LSD in my Spec E46.
For future jobs, if you tackle this again, I just buy new bearings for the new diff.
In reply to docwyte :
I actually already ordered and received the correct gear oil (the Motul 300 75w90 pictured above), but I appreciate the offer!
In reply to jgrewe :
I appreciate you catching that and informing me! I agree with information about these diffs being relatively scarce. I'm ever-so-slowly writing an in-depth swap guide that I'll be posting to my blog and sharing in a few key locations to hopefully help others learn from the mistakes I've made and know what they're getting into. A few of the other blog posts I've created (namely coding out DME nannies, installing an OEM oil cooler and installing an oil pan baffle) have received quite a few views, so I'm hoping they're at least helping people not have to struggle with the lack of information out there for these cars.
You know, I considered buying new bearings. Money wasn't a factor. I just followed along with what most of the YouTube guys were doing (re-using stock bearings). I wasn't sure why they re-used their stock bearings. More specifically I wasn't sure if they were concerned with new bearings potentially throwing off the backlash, thereby forcing them to start experimenting with a plethora of not-exactly-cheap shims/snap rings.
I actually just looked on ECS Tuning's and FCP Euro's websites... I didn't see new races available at all, which is unfortunate, as I would have liked to have used new races, if for no other reason than to avoid the process of removing the old ones from the stock diff.
The only set of bearings I saw were from MFactory for $180, which, again, I would have considered buying if I knew it wouldn't be a problem that required using new shims. But like pretty much everything else with these cars, solid, reliable information is pretty scarce, so I just followed along with the YouTube guys and re-used the stockers.
Today I took a few minutes to remove the old interior air vents and replace them with the ever-so-slightly not-quite-as-terrible versions I pulled out of a junkyard.
The old vents:
They popped right out in just a minute or two. I then popped the new-to-me junkyard vents into place:
^^^Not quite a night-and-day, "OMG, it's brand new" improvement, but a slight step in the right direction. I might get some plastic restoration stuff and really clean them up one day.
I also figured that while I was waiting on the new axle seals to get here, I would take a bit of time and clean up the rust that was previously covered up by the stub axles:
I then did something pretty childish. I went on eBay and ordered an E9x 335iS badge. I only ordered it in order to use the "S" portion of the badge to make my trunk say "128iS". I don't believe BMW ever produced a 128iS, but with the 3SIM, upgraded Bilstein suspension, upgraded OE "M" control arms, an OEM oil cooler, a baffled pan, upgraded wheels/tires and now with the upcoming shorter gears + LSD, it seemed fitting. I figured if BMW ever made a car with similar specs, they would have called it a 128iS.
I don't think I've ever put some silly badge on a car before. I suppose there's a first time for everything.
It will only matter to people who know, so 99.99% won't bat an eye. The .01% will chuckle, that is all we care about.
I had a friend that had the Porsche "SC" letters from a 911 on his stockish 1990 Jetta. The fun part was, at a Porsche track event he got a point by on the pit straight at Mid Ohio from a 911SC. There had to be 25 people that saw it happen,lol.
In reply to jgrewe :
Ain't that the truth! 😂
All those years I owned Honda's and I never added a single VTEC, SiR or Type R badge! So many missed opportunities!
The axle seals came in last night. I installed them.
Re-installed the stub axles and filled this thing up with Motul fluid. Finally, I think everything is ready to swap the pumpkin into the car.
Stock diff removed.
I might wait on a buddy to stop by before I mount the new diff back in the car, as it seems like a second set of hands would be helpful at this point.
New diff/LSD is in and everything is torqued down.
I still have to button the other minor things up (exhaust, heat shield, wheels, etc) and code out the eLSD, but I ran out of daylight and didn't feel like crawling around on my back with a flashlight. So, I'll likely finish everything up in the morning.
Did you replace the subframe bushings with solid inserts?
In reply to OHSCrifle :
I installed Whiteline rear subframe bushing inserts a long time ago, but they're not solid per se.
I plan on eventually replacing them with solid aluminum rear bushings (likely from Revshift), but that likely won't be for quite a while.
The only thing I'm doing right now is the 3.73/LSD swap. This has been a month-long project. It'll be a while before I get the motivation to move onto the next project 😂
Finally. It is complete.
I went full DIY blog on this one. Hopefully it helps anyone that is thinking about swapping a LSD into an E8x/E9x car.
Be forewarned: it's a long write-up. Lots of words and lots of photos. Best of luck, gentlemen!
After doing some more spirited driving on the street and bringing my wife along for the ride, I actually just made a new post with more street-driving impressions for anyone that might be interested:
After installing the 3.73 LSD diff, since the car was already off the ground and it's almost October, I figured I would swap out my summer wheel and tire setup, going back to the OEM wheels and Continental tires. Granted, I've been spoiled with the much stickier, stiffer rubber, but upon driving around my neighborhood, I remembered why I don't like these Continentals: they're just too soft. The amount of roll they introduced was truly eye-opening. So much so, that my wife noticed the extra roll from the passenger seat without me saying a word.
I know a lot of people like them. They're fairly quiet and comfortable. They have a bit more grip than you would expect from such a mushy-feeling piece of rubber. But man, the steering immediately gets lazy and they just make the car feel so soft that they turn me off.
To be clear, aside from my work car, I'm down to just the 128i and my Mazda 3 Turbo. Translation: the 128i is technically my only "sports car". And these tires kill the sporty feeling that I enjoy when pitching a RWD coupe around on a back road.
So, despite the fact that they still have plenty of rubber left on them, they've gotta go. I don't care anymore, I'm just not willing to spend another 6 months driving a "sports car" on these squishy things. I put my money where my mouth is:
^^^If these would have been available when I bought the Continentals, I would have just ordered them. Or if they were, I don't know how I missed them. Typically, for summer street tires, I'm a huge Michelin Pilot Sport fan (they're my favorite summer street tire). I've never ordered the all-season variant before. This should be interesting. I'll be sure to post a comparison of my thoughts.
I spent some time reading through reviews on Tire Rack's website... common complaints about the Michelins seem to be that they're noisy and ride rough... but all comments on the handling front seem to suggest they're superb for an all-season. They sounded right up my alley. Only one way to find out.
