128i Blackline Helical Differential Install

[TimCSquared]

This will be my first big thread, and it requires some backstory. I am a Mechanical Engineer currently pursuing a Masters Degree. I am also a member of my university’s FSAE team, and have been for 5+ years. As such, I have the unusual combination of experience, access to tools & resources, and absolutely no money whatsoever. This is reflected in my… unorthodox diff installation.
If anyone wants my input on something racing related, I’d love to share some of what I’ve learned. I mainly do suspension/chassis adjustments (on more than just Formula cars), but I have some experience in most racing-related fields.



I bought a Helical diff From Blackline. I chose the 188L option. Getting a clear answer for which you need is difficult, but all signs pointed to the 188L for my ’08 128i 6MT. Perhaps this was incorrect – more on this later. The Blackline is a 12 planet helical diff with 6 preloaded Belleville washers in the center. From what I understand, this is essentially a copy of the Quaife unit.
You also need 2 axle seals, CORTECO PN# B1BASFSLDRWX27, $20 for the pair on eBay.
I will use Redline 75W90 Synthetic Diff Fluid, however there is a 500 mile break in period, and you change the fluid after to remove any burrs or particulate which may get ground away from the faces of the gears or gear bores. Normal stuff, really: The particulate/swarf can be lessened by more stringent surface finish tolerances during manufacturing, but is applicable to any diff. I threw in some junk 75W-90 Oil for the break-in. It took a little less than a quart from bone dry.
There are plenty of YouTube videos online describing the procedure, but I will document my experience below anyways.

Removing the Pumpkin from the car:
For a 128i non-Msport, this is easy. Obviously, you will need to jack up the car. Each CV is bolted to the output shafts using 6x bolts with an E12 head, remove these. The Driveshaft is attached to the pinion flange using 4x bolts with an E12 head, remove these as well. There is a centering bore between the flange and the driveshaft. Both the CV bolts and the driveshaft bolts are tight enough to probably require putting the car in gear/handbrake to allow you to loosen them without the wheels spinning. The exhaust hangers are bolted to the backside of the front diff bolts. For my single exhaust, there is just one, remove these. Now, support the diff using a jack, and remove the rear bolt and two front bolts. (Rear: 21 mm Wrench, 21mm Socket Front: 18mm Wrench) The front bolts are halfway under the heat shield, so I went slowly with a wrench to get them out. Alternatively, you could drop the heat shield and using a ratchet, or get a swivel head ratchet to speed things up. Lower/Drop the diff using the jack and slide out. 1-2 Hour Job.

Removing the center from the Housing:
First, make sure you can get the fill plug out. You want to figure that out as soon as possible. Remove the cover bolts (8x w/ 16mm head), and drain the “lifetime” diff fluid. You will immediately notice that this fluid is not, in fact, a lifetime fluid. As an oil breaks down due to excessive heat or heat cycles, it produces a very distinctive smell. You’ll see what I mean.
Take a hammer and punch and knock the Output Flanges out the sides. Now you need to get the seals out. I used a seal puller (thank you FSAE team), and it took all of 20 seconds. I think you can probably do this with some screwdrivers and some luck. Beneath the seals are the thickest snap rings you have ever seen, and they are not willing to cooperate. I had access to the correctly sized snap ring pliers, and they were still a PITA. They like to stick in the groove.
With the snap rings (hopefully) out, slide the bearings out the sides. Try to keep them from going inside the housing, you want to pull them out the sides. If they go in, you can get them out still, but it’s much harder. Then, push the center section to the right, and rotate the ring gear up and out.

Modifications:
With the center section out, you will need to grind a portion of the case away. This is on the Lefthand side (from driver perspective, imagining if the diff was installed), above the bearing on the sealing surface for the cover, as shown in my picture. Be careful about metal shavings or grit getting into the pinion gear, the pinion bearings, or the area behind the pinion gear. With the new center section, the ring gear will hit this part as you try to install it.
Unbolt your ring gear from the old center section. I used an impact driver, because I had one available. But the old center section has two big flats cut out where you can see the spider gears, which fit perfectly into a vice if you need to use a breaker bar. Leave two bolts threaded in by a few threads (opposite each other), hit them with a hammer, and knock the ring gear out.
Now, remove the bearing races. They are pressed onto either end of the center section. Thankfully, BMW left a few cut-away sections so you can get under them, but it is still no easy task. I kept all the left parts and right parts separate, so I didn’t mix them up when reassembling.
Here’s where things really fell apart. My diff center has the ring gear flange too far from where it should be, as it is on the stock unit. I’m not sure if that is because I bought the wrong one (188L vs 188K, vs etc.) or if this is one of those you-get-what-you-pay-for situations. Luckily, I have access to a machine shop, and have worked as a machinist for a few years. I measure the discrepancy and make a spacer to go under the ring gear, which is thicker than necessary. Reassemble, check it, disassemble, machine the spacer down, repeat. Each time I checked the backlash until I got it just right. Birds Auto and Quaife specified 0.0024” to 0.0055” Tangential Backlash. I machined the spacer until I got 0.0035”
How are you supposed to do it? Well most people will tell you that this differential cant be adjusted, but there are still ways to do it. I’ve heard of people using thinner snap rings outside the bearings and putting spacers between the snap rings and bearings. This will do the trick, but it will also move the bearings over. For small amounts, this is fine, but I needed to move over 0.2685”. The downside with how I did it is that if the spacer isn’t exactly the same thickness, the gear engagement will change as it rotates. To alleviate this, I was just very careful and measured it afterwards to make sure all was okay. Flat within 0.00015”.
It would also be a good idea at this point to check ring gear and pinion engagement with gear paint or Dykem Bluing Compound.
I also needed longer bolts, Grade 10.9 M12x1.5mm, 30mm Long, w/ Washers 2.5mm thick.



Reassembly:
Clean the housing, torque the ring gear w/ Loctite, reinstall, put the bearings in, then the snap rings. The seals get pressed in, I used a hammer and a piece of aluminum tube. Reinstall the output flanges, they will require a few good blows with a dead-blow hammer. RTV the cover, and reinstall that too. I filled with fluid on the bench while I was at it.
Putting the pumpkin back into the car is the reverse of removal. 3 Diff mounts, 12 CV bolts, 4 Driveshaft bolts.



Breaking it in:
First off, do a few sharp left hand and right hand turns, this will circulate the diff fluid up into the helical gears. Drive the car like a normal person for 10 miles. After that, you should be good to go, just flush the fluid in 500 miles.

Was it worth it?:
The whole process took me a total of two days, and that was with a well-equipped shop to play in. IT was a lot of hard work. Was it worth it? Absolutely.
As can be expected, corner exits are massively improved, especially for small radii. Oversteer recovery is also much easier. Launching yields more acceleration. Yada yada yada. The car feels great. It should have come with a LSD from factory.

Useful Resources:
Blackline Diff Disassembled: https://z4-forum.com/forum/viewtopic.php?t=102831
Bird’s Auto Install Instructions: https://www.birdsauto.com/sites/defa...68303%20v4.pdf
Diff # Identification: https://www.1addicts.com/forums/show...3&postcount=49
More Info about Stock Diff Configuration:
https://www.1addicts.com/forums/showthread.php?t=466621
https://www.1addicts.com/forums/showthread.php?t=935123
https://www.e90post.com/forums/showthread.php?t=1472442

In case anyone needs to make a spacer for themselves, mine was 0.2685” thick, 6.6” OD, 4.7” ID, with 10 0.5” holes spaced evenly on a 5.32” circle.

[spidertri]

Very cool writeup, I was wondering what it would take to put an older LSD unit into our diffs.

I believe what you ran into with needing the spacer is the difference in low vs high ratio units. If you look at MFactory's catalog, for example, you'll see listings for 188 diffs under the 3.07 ratio and a different listing for over 3.15.

[mad_hatter]

I would echo spidertri comment about having the incorrect ratio carrier. There is a carrier break in these units for <3.07 and >3.15

It would seem you have the <3.07 unit and your diff is a above the break. In my experience numerically lower ratios will use a significantly larger pinion head, and therefore need more space between the pinion head and ring gear mounting surface to achieve the correct backlash. Since your ratio is numerically higher, you had to fabricate the spacer.

Do you have the link to the Blackline diff you purchased? That will help confirm the idea.

[TimCSquared]

Link is below:
https://www.ebay.com/itm/401789956792
The seller also lists another 188L diff advertised for the 1 series:
https://www.ebay.com/itm/153446641798

The listings are identical as far as I can tell.

The different gear ratios are a superb explanation. I had never considered that. Or rather, I guess I had assumed that the spacing (between ring gear landing and pinion center-line) would be identical so switching between parts would be more convenient. This way, the thickness of the ring gear would be different depending on the pinion pitch diameter.

P.S. mad_hatter, I am classed in STX as well down in Texas. Let me know if you'll be at SCCA Nationals in Nebraska this September. I will be there (not driving the 1er).

[mad_hatter]

Originally Posted by TimCSquared

Link is below:
https://www.ebay.com/itm/401789956792
The seller also lists another 188L diff advertised for the 1 series:
https://www.ebay.com/itm/153446641798

The listings are identical as far as I can tell.

The different gear ratios are a superb explanation. I had never considered that. Or rather, I guess I had assumed that the spacing (between ring gear landing and pinion center-line) would be identical so switching between parts would be more convenient. This way, the thickness of the ring gear would be different depending on the pinion pitch diameter.

Your assumption is 50% correct. That is what manufacturers do, but there's a limit to the number of ratios they can build the carrier to accept. In the case of the 188L, BMW made one carrier for 3.08 - 3.91 and a second one for the <3.07. I noticed in the link they specifically call out 2.79 ratio and mostly diesel applications, which would all use numerically lower gear ratios (they don't need the torque multiplication, and also it will keep their engine speeds lower at a given road speed and tire size).

Originally Posted by TimCSquared

P.S. mad_hatter, I am classed in STX as well down in Texas. Let me know if you'll be at SCCA Nationals in Nebraska this September. I will be there (not driving the 1er).

It will depend largely on what the border situation and quarantine rules are, since I'm Canadian. There's a group from my region who regularly go down and invited me along whenever we're able to go again!

[spidertri]

TimCSquared

What torque spec did you use for the ring gear bolts? I'm getting ready to torque mine, I see specs all over the place from 80ftlb to 125ftlb. At one point BMW spec'd a TTY bolt but now they don't.

Fastenal torque chart shows 92ftlb for M12 12.9 bolt with lubricated threads.

[wootloops]

Just ordered one of these for my 128. I got the one listed as 188K since it specified that it fits in the 128i and 328i with the higher final drive ratio. Hoping that means I avoid the issue where you required a spacer.

Just need to figure out what I am going to do for a bearing/install kit. I plan to source a lower mileage 3.73 rear end from a local salvage yard (~60k miles). I'm not sure how hard it is to get the bearing race off of the stock open diff... maybe I can just re-use them and get new seals?

[spidertri]

I reused the bearings from my stock diff. Had to very carefully make some notches in the open diff so that I had room to get the bearing puller jaws on the race. Then it was very easy to get them off.

Put the new unit in the freezer for a while and the bearing races will go on easily. Just make sure you're ready to put them on right as you take it out of the freezer, it warms up quickly.

I checked my backlash and tooth pattern and all was good, I didn't need different shims. Just new seals and fluid.

[ZarathustraDC]

Originally Posted by wootloops

Just ordered one of these for my 128. I got the one listed as 188K since it specified that it fits in the 128i and 328i with the higher final drive ratio. Hoping that means I avoid the issue where you required a spacer.

Just need to figure out what I am going to do for a bearing/install kit. I plan to source a lower mileage 3.73 rear end from a local salvage yard (~60k miles). I'm not sure how hard it is to get the bearing race off of the stock open diff... maybe I can just re-use them and get new seals?

Did all 128’s in the US come with the same final drive ratio?

[wootloops]

Originally Posted by ZarathustraDC

Did all 128’s in the US come with the same final drive ratio?

I believe all manual 128i in the US come with 3.23.
US market Automatic 128i and most (all?) RWD 2007+ E90/E92 328i came with 3.73.

In my research it seems the automatic 128i diff may have something different about it (compared to the 128i manual rear diff), and everyone seems to use 2007+ 328i units... not sure if the sizing or flanges are different but that's what RealOEM lead me to believe.

You can also frankenstein a 3.91 ratio from an X-Drive E9X car but that requires swapping the driveshaft input flange and isn't quite as straightforward.

So, I personally just ordered a 3.73 auto RWD diff from a 2009 E92 328i and will be using that for my LSD install.

[TimCSquared]

Originally Posted by wootloops

Just ordered one of these for my 128. I got the one listed as 188K since it specified that it fits in the 128i and 328i with the higher final drive ratio. Hoping that means I avoid the issue where you required a spacer.

Just need to figure out what I am going to do for a bearing/install kit. I plan to source a lower mileage 3.73 rear end from a local salvage yard (~60k miles). I'm not sure how hard it is to get the bearing race off of the stock open diff... maybe I can just re-use them and get new seals?

I reused my bearings. I forget how I removed them, but I remember it was relatively easy. I either pushed them out with my hands or gently used a punch and hammer and it came out smoothly. BMW doesn't put much of a press-fit here.

You will almost certainly need new seals. After destroying my OEM seals, I could probably remove them without destroying them, but it's worth it to replace them while you have it all open.

[Spielmp3206]

Originally Posted by wootloops

I believe all manual 128i in the US come with 3.23.
US market Automatic 128i and most (all?) RWD 2007+ E90/E92 328i came with 3.73.

In my research it seems the automatic 128i diff may have something different about it (compared to the 128i manual rear diff), and everyone seems to use 2007+ 328i units... not sure if the sizing or flanges are different but that's what RealOEM lead me to believe.

You can also frankenstein a 3.91 ratio from an X-Drive E9X car but that requires swapping the driveshaft input flange and isn't quite as straightforward.

So, I personally just ordered a 3.73 auto RWD diff from a 2009 E92 328i and will be using that for my LSD install.

Hi I am closing the deal for a manual 128i, the seller told me the diff ratio was changed to 3.73, I plan to install an LSD , is there something I should be taking special attention when ordering it ? I don't know if the car had the full diff unit changed or if only the gearing was changed, is there a way to check that ?

Regards

[wootloops]

Originally Posted by Spielmp3206

Hi I am closing the deal for a manual 128i, the seller told me the diff ratio was changed to 3.73, I plan to install an LSD , is there something I should be taking special attention when ordering it ?

Any LSD you order should say that it is for an E90 328, and that it is for gear ratios greater than or equal to 3.15. There seems to be a lot of confusion between 188K and 188L so I just go by automatic 328 with that correct gear ratio.

I don't know if the car had the full diff unit changed or if only the gearing was changed, is there a way to check that ?
Regards

it will say 3.73 on a sticker on the top, but you won't be able to see it on the car easily. However, I really doubt they swapped just the ring & pinion because that is a lot more work than just swapping the whole unit, and would probably not be any cheaper. Salvage yards typically sell the whole unit and don't bother breaking it down because of the labor involved.

[wootloops]

Trying to install the races on my blackline LSD and hitting a snag.

I see that the bearing race sitting on the factory carrier goes down past the carrier. It's not flush, the carrier protrudes out of the race maybe a couple of MM.

Example:


But now trying to press the race onto the blackline, I have only gotten it this far (Flush with the end of the carrier):

View post on imgur.com

I don't really know what I can use to smack it on there... it's like maybe 48mm ID? I tried using a piece of PVC coupler but I don't think it's strong enough.

I noticed in the OP's picture the race isn't fully installed.

What did you guys use to get it all the way down?

[spidertri]

I looked through all the pictures I took of my install but don't have one that clearly shows that race installed. Granted, I didn't use a blackline diff but I remember it seating pretty much to the exact same gap (to the body) that it had on the stock open diff.

How far off are you? I don't see any reason why you couldn't use a socket or pipe to push it further down. 48mm is close to 1 7/8", just make sure your only on the race and not the diff stub.

[wootloops]

Yeah I ended up dropping it off at the local machine shop so they can just press it all the way on. Hopefully picking it back up soon. I didn't have a socket that was large enough to go around it unfortunately and didn't want to risk damaging the race.

[wootloops]

Ok, so an update and info for anyone who does this in the future:

I got my Blackline helical LSD installed. Test drove it and even did an autocross this weekend and all seems good! For reference, mine was the one listed as "188K" and it fit perfectly into my housing from a E9X 328i with 3.73 gear ratio. I did not need to fabricate a spacer like the OP of this thread above. My donor was a 2009 E92 328i with like 80k miles.

Differential Disassembly Notes:

First step was to remove the output shaft flanges from the diff. I did this using a pry bar against the housing pushing on the flange. Try not to bend the dust shield that surrounds the flange against the diff (but you can bend it back carefully if you do).

Then I removed the diff cover. I also scraped all of the RTV sealant off with a plastic razor and then later gave the mating surfaces a light sanding to clean it up.

The next part is kind of a pain, removing the snap rings. I got some big ass snap ring pliers (CTA Tools 4031M) that helped a lot. But still had issues with them slipping off, so I put a little electrical tape on the tips of the tool to give it some grip. Then you have to kind of wiggle the rings back and forth before they will break loose from the housing and come out (carefully). Wear safety glasses because if they come off the pliers under tension they can really fly at you.

Once you get those out you should be able to push the outer bearing race out from the inside of the diff, they aren't that tight. You just have to push them evenly or they get stuck. If that happens just try to push them back in and start over. Once you get the right side out you can probably roll the open diff out of the housing carefully. Then remove the other side. Dont quote me on that order I cant remember exactly how I did it.

Once the open carrier is out of the housing I removed the ring gear bolts with an impact gun and set the ring gear aside.

After that I tried to get the inner bearing races off. Since mine was under 100k miles I decided to re-use the bearings. If your diff higher mileage you may want to closely inspect the bearings and races to make sure they are smooth with no pitting, grooves, etc. Getting the inner races off the carrier is kind of a pain. One of them is easier than the other. I used a bearing separator from amazon (named "YOTOO Bearing Pullers Set 5 Ton Capacity, Bearing Separator Kit" but there are many others similar to it). I paired that with a piece called "OTC (8061) Step Plate Adapter" that allowed me to pry off one of the inner races. The other one, as others have stated, requires you to use a dremel or grinder to CAREFULLY cut away material around the race. Otherwise you cant get the tool under the lip of it to pull it off. The hardest part here is cutting without accidentally hitting the race surface with the bit so take your time.

Differential RE-assembly Notes:
At this point it's reassembly time. First I tried to use the freezer method to freeze the new LSD and then heat the bearing races to install them onto it. This kind of worked but I didn't have anything that could press the race all the way down. If you get the right size socket you can probably make it work but I found a local machine shop and they pressed them on properly for like $20 so that was way easier. You need the races to go all the way down onto the LSD so don't skimp here.

I also had a hard time torqueing down the ring gear bolts because I didn't have a proper vise to holt the LSD still. So, I also let the machine shop do this for me. I specified 100 ft lbs and red loctite. I did re-use the stock ring gear bolts.

With the LSD itself assembled with the ring gear and bearing races, next I installed the other (outer) race into the right side of the diff, as well as the snap ring on that side. Then, I was able to carefully rotate the new LSD into the housing. You put the right side in first and then carefully rotate it. I did not have to grind anything away like others mentioned, I just maneuvered it carefully but it really wasn't difficult.

Once the diff is sitting in the housing with the one side bearing in place, you carefully install the left side bearing race and snap ring. I found that it was easier to do this with the housing on its side. I used a large bushing install cup to tap both sides in, as well as the snap ring. It was just the right diameter to fit into the side of the opening. Just be careful to not scratch the inside of the opening otherwise the output shaft seal may leak. A PVC pipe of the right size may be safer, and then tap it with a small hammer / mallet.

Once I got the left side in, I carefully tapped on the output shaft area of the diff from the right side to make sure that it was pushed all the way in. I did this because I was getting some tight backlash readings and I wanted to make sure the diff and ring gear was seated properly in the housing. This may or may not have helped.

Then I checked backlash with a dial gauge on a magnetic mount. At first I was getting like .0020 which was too tight (spec is .0024 - .005 I believe). I then took it back apart and tried carefully sanding down the left side snap ring to shift the diff in the housing away from the ring gear. It didn't seem to do much but after re-assembling and tapping the diff as mentioned above, I was able to measure .0030 backlash. I also painted the ring gear with marking compound and saw a pretty good pattern right in the middle of the teeth so decided to wrap it up.

After that I installed the cover with permatex ultra black, filled it up with 75w90 gear oil, and put it in the car. No weird noises and it lasted 1.5 hr high way drive and an auto-x. The car really feels transformed with the 3.73 and the LSD. Highly recommend this mod. Can't speak to the long term reliability of the Blackline but it seems to be made well enough for the price and I think it's worth rolling the dice.