[BB_cuda]

Notes for Swapping the BMW 215 size differential: 2/11/17

I had a spare 2.81 ratio differential sent to HP Autosport in Santa Barbara, CA. Work was done on my welded diff to convert it over to bolted type ring gear and a Wavetrac LSD was bolted on and proper backlash set to retain same backlash prior to the machining work. thanks Harold and thanks Autotech.

Differential swaps have been covered many times in the suspension/chassis/brakes section of E90post. I will list the basics for getting to the point of directly working on the diff and then provide more details at that point.

NOTE: I cover switching over to a finned differential cover but factory exhaust may have interference with the lower driver's side fins. The 1addicts thread that I attach in post 2 shows how some 1 series and 3 series gassers had to trim the lower left fins some. Post #87 in that 1addicts thread shows an excellent picture of that trimmed cover. My aftermarket exhaust cleared by about 5/8" to 3/4" (I'll go do a final measurement and edit it in), so no trimming was necessary on my part.
torque specs:
• Driveshaft nut, Spec 26 11 1AZ, 85 N-m, 62.7 lb-ft (modify for using crows foot, covered later)
• 1/2 shaft screws, Spec 33 21 1AZ, 70 N-m, 51.6 lb-ft
• Front diff bushings, Spec 33 17 1AZ (12 mm), 100 N-m, 73.8 lb-ft
• Rear diff bushing, Spec 33 17 1AZ (14 mm), 165 nm-m, 121.7 lb-ft
• Diff cover bolts, Spec 33 11 1AZ (10 mm), 90 N-m, 66.4 lb-ft
• M22 fill screw, Spec 33 11 2AZ (22 mm with o-ring), 60 N-m, 44.3 lb-ft
Special tools:
• 27 mm wrench or 1-1/6” box end wrench (for rear side of rear diff bushing)
• 21 mm socket for front side of rear diff bolt head (21 is not a normal size that comes in a socket set)
• 50 mm thin crow’s foot wrench, available from a couple vendors, I borrowed one from generous forum member and will be passing it on per his instructions to next diff installer.
• Transmission jack
• A lift would be quite helpful but I did the job on jack stands (as usual)

PARTS LIST:
• (3) Liters, Motul Gear 300, 75W-90 gear oil(break-in and change after 1000 miles), bought this on ebay, $59 for 3 Liters, free shipping
• 33-32-6-770-288 rear diff bushing nut (M14x1.5 ZNS3). I call this the 0288 nut below, bought from local dealer, Husker has them for a hair less than dealer
• (12) half shaft screws- p/n 33-20-7-572-716 (M10x43 mm long), bought from Husker
• Blue Loctite for the ½ shaft screws, purchased from local parts store
• Insert nut for driveshaft to diff connection- p/n 26-11-7-567-770 (M39x1.5x16.5 mm), bought from Husker
o This comes with a new seal and plastic retainer clip
• Sealant for cover, p/n 83-19-0-404-517, Loctite 5970 liquid sealant, bought from Husker, Typo corrected on 3-14-17
• The following are only needed if you are switching to the finned cover shown in photos
• Finned rear differential cover p/n 33-11-7-519-661 ($128 at Husker site, https://www.bmwdirectparts.com/ )
• Bellmetric 14x1.5X140 mm bolt (10.9 grade)
https://www.belmetric.com/14x15-fine...4jv5u14r9ohop0
• 9/16” ID hardened washer OR 14 mm ID hardened washer (used on 14 mm bolt since it doesn’t have a flanged head), use Bellmetric link above and hunt for it
• 1-1/4” OD x 9/16” ID X 5/8” thick aluminum spacer, machined by local shop, I paid $75
• (1) M10x 25mm, P/N 33-11-7-521-292 (cover bolt, deleting 75 mm for a 25 mm one) see photo, bought at Husker
PREP THE NEW DIFF:
• Built unit was shipped back with cover off
• Check that unit does or does not have stub axle seals and retainers
clips installed. OmahaDZL, Whitbread, and I learned that Autotech as
a default doesn't replace these. Omaha will elaborate in a post below on
his experience and resolution. If no seals and clips installed, STOP and do this BEFORE adding lube and/or installing the new diff.
• Install either original cover or finned cover
• Apply Loctite 5970 sealant on lip of cover, I spread it out sort of thin with finger tip
-original uses (6) 25 mm and (2) 75 mm long screws
-finned uses (7) 25 mm and (1) 75 mm long screws
-torque to 66.4 lb-ft
-I let it cure over night
-load diff with gear oil through fill hole and torque to 44.3 lb-ft with 14 mm male hex.

GET THE STUFF OUT OF THE WAY:
• Supported car on 4 jack stands at normal rocker panel located jack points
• Removed fore to aft support bar of uhaul receiver hitch [Doesn’t apply to stock car]
• Removed under trunk stored compact spare tire [Doesn’t apply to stock car]
• Removed the plate that spans across “floor hump”
• Removed the exhaust’s mid pipe and rear pipes
• My exhaust is very easy to remove because it is 3 piece design.
OmahaDZL still had OEM big motha 1 piece in. He was able to remove
diff without removing exhaust. He sort of rotated it down and it came
down between the pipes. He did have "fun" with the midpipe exhaust
rubber isolators being in his way. These are the ones that are
connected adjacent to the 2 front diff bushing screws. He said after the
fact that he should have pulled those off the welded on exhaust hanger
rods for more clearance. WD40 and channel locks may be your friends
here.. If you do take Omaha's simpler route, be advised this
may possibly run you into trouble for pushing diff back up in there if
you go with the finned diff cover. MEASURE carefully if you 1)don't pull
exhaust and 2) use finned cover.
• Removed the heat shield that spans from back of floor hump plate to
close to aft end of drive shaft
• Per OmahaDZL install experience, the DEF tanks are in the way and
make it more difficult to do the work on the back side of the subframe.
Maybe this isn't a big deal if you're working on a lift. Omaha and i did
this job on jack stands though. Again, I benefited having the DEF tank
"ectamy" already behind me.
ONTO THE DIFF ITSELF:
I used old belts that don’t fit me anymore but you get the idea. Use wire, rope, whatever you have that will support the ½ shafts and driveshaft from falling down after unbolting. I allowed more of a droop for the driveshaft for when I was doing the final pull to achieve an angle to slide out the splines of the diff to driveshaft. There are a couple pictures showing all three shafts being tied up.

I borrowed a transmission jack locally and a 50 mm crow’s foot wrench from a forum member. It is advised to loosen the driveshaft’s 50 mm nut while the half shafts are still connected and the emergency brake is applied. There have been several discussions on the boards about which way to turn the nut to loosen the connection. The nut is threaded onto the driveshaft and it is a normal right handed thread. Thus, if you are looking aftward, the nut will need to be turned clockwise. If you know what right hand rule is, the nut is turned in the direction of your curved fingers and your thumb points in the direction that the nut’s axis advances towards. I have a graphic pasted into the pictures that comes from the online workshop manual. I really struggled here but will spare you and explain what needs to be done to more easily free up the nut.
• CLARIFICATION: Turn the nut from the driver's side to passenger side
when looking from the bottom. This is equivalent to my wordy, techno-
geeko explanation above. To my defense, the graphic below is showing this same thing. Picture is looking aft ward.
• DON’T BRACE WITH THE BI-HEXAGONAL NUT WHEN WORKING ON THE 50 mm NUT! LEAVE IT ALONE!
• Slide the crow’s foot up onto the 50 mm nut with a breaker bar inserted into the ½” drive’s square hole. Skinny guys like me slide a cheater bar onto the breaker bar too.
• Turn the nut as shown in the graphic. You will have to move the crow’s foot many times. I was only able to turn it about 2 revolutions before encountering SIGNIFICANT resistance.
• Turn the nut in the opposite direction about same 2 revolutions. This helps to break up the Loctite that is inside the nut. It turned fairly easy in comparison to previous step.
• Go back to turning in the clockwise direction per the graphic. OMG, it was so much easier to turn in comparison to 2 steps earlier. Eventually, whitish powder started falling from inside the nut and this was great news that the Loctite had been broken up. Continue turning until it’s pretty much freewheeling.

Disconnect the 2 half shafts from the sides of the diff. You will need an E-torx socket here. If memory serves, it is an E-14. I found it easier to put car in neutral with e-brake off. I would turn either wheel to get optimal position on each of the 6 half shaft screws. The optimal spot seems to be with screw at half way point between bottom and top to be able to get the socket on. I held the wheel with one arm while un-torqueing with the other. The passenger side was easier as I was able to hold arm (very large spoke) of wheel to resist the torque. On the driver’s side, I got help from someone to intermittently apply and remove the e-brake as I un-torqued that side. It is sort of weird to try to finesse the half shafts out of the diff’s output flanges. I then tightened the belts to have the half shafts above the diff’s side flanges. This is so they don’t hang it up when it’s brought downward on the transmission jack.

Bring transmission jack under and properly support the differential. I used the ratchet strap to hold it onto the jack as an insurance measure.

Disconnect front differential bushings and remove the long 12 mm bolts. Disconnect the rear bushing that uses a 14 mm bolt. It takes a 21 mm socket for front bolt side and I measured the back “0288” nut (that’s the last 4 digits of the part number) and it’s a 27 mm. I don’t have that size socket but a 1-1/16” wrench fits it well. 27mm=1.06299” and 1-1/16”=1.0625”. I have giant wrenches to work on my old Plymouth.

At this point, your diff is only still connected by the splines of the driveshaft. I next lowered the diff down some by easing the jack’s height down. I then started steadily pulling on the diff/trans jack combination and slowly it started showing splines. Eventually, it was free. See picture of diff on trans jack out in driveway.

You need to clean the external threading on the driveshaft. I used an old tooth brush and some WD-40. Whatever you think will get the majority of the old Loctite out of the threads. A new 50 mm nut, gasket, and retaining plastic clip is needed on the new diff. Note that the new nut has Loctite inside it as well.

The cup that the insert nut goes into on the diff needs to be cleaned out and re-greased. I used normal lithium grease. I asked dealer techs if there was anything special and was told normal grease was fine. The nut has an elliptical flange on it and it enters into the cup that is also slightly elliptical. Put seal on first, then insert nut’s flange, and then snap the clip over the seal. Also, the internal splines on the driveshaft need to be re-lubed with same grease. I added a small amount. You don’t fill up the internal spline cavity or won’t be able to push the diff and driveshaft together as the grease will be pressuring up and not allow the diff’s splines to fully seat. You’re lubing, not loading a canon.

I sort of learned as I went along and putting it back together was actually easier. I recall reading that I only had 5 minutes to get the driveshaft nut on and torqued back to 85 N-m (62.7 lb-ft). I took longer than 5 minutes and was fine. Torquing with a crow’s foot induces an error. You are using a longer lever arm than the torque wrench knows about. In my case, the torque wrench was 15” long from center of wrench to center of hand grip. Crow’s foot has an extra 2.25”.

Here is a link that explains it. http://www.engineersedge.com/manufac...e_wrench_1.htm
In my case, T=62.7 lb-ft, L=15, E=2.25, Y=(TxL)/(L=E)=(62.7x15)/(15+2.25)=54.52. For those that don’t want to mess with it, using my L and E values, the torque will be 15% high or 72.1 lb-ft. The point of the formula is I set the torque wrench at 54 lb-ft to get an actual of 62 lb-ft.

I stabbed the diff’s splines into the driveshaft, seated it as far as I could, and turned the nut a little bit (2 turns, approx) to get it engaged. I then jacked the diff up into position. I undid the ½ shaft belt supports and finagled the shafts into place. It was a little bit of a left and right push of the diff to get both shafts into the flanges. I then put the (2) 12 mm front bushing bolts in and threaded them in about ¾ the way up. I didn’t torque them but wanted to keep diff from twisting while I torqued the driveshaft nut as discussed above.

Next up was the rear bushing bolt. I stray from the OEM path here. If you have the standard cover, reuse your 14 mm bolt that is approx 112 mm long. I still think BMW spec’d it too short but it will obviously hold with the 33326770288 nut. I used an aftermarket bolt from Bell metric that is 140 mm long x 1.5 mm pitch. You need a hardened washer with it. I got a 14 mm washer from Bellmetric but a 9/16” hardened washer will work too. The Bellmetric bolt doesn’t have a flanged head like the OEM 112 mm long bolt does. Thus, the need for the washer under the bolt head.

The finned cover has a boss on it for the rear bushing. It is offset further forward that the OEM cover by a little more than 15 mm. This is where the aluminum spacer comes into play. The spacer goes between the back of cover’s boss and front of rear diff bushing. It took a bunch of fiddling around to get alignment here to be able to push the 14 mm bolt through. I got bolt through the bushing and slid the dog bone (p/n 33-17-6-773-193) back onto the bolt. Lastly, thread the new 0288 nut onto the 14 mm bolt. I went back and snugged up the (2) forward bushing bolts . Returning to rear bushing bolt, I torqued to 121.7 lb-ft (per list at top of this writeup). Specifically,I used a 1-1/16” socket and put this onto torque wrench. The bellmetric bolt has a 22 mm head on it (OEM has a 21 mm head). I braced front with a breaker bar and torqued on nut side as torque wrench wouldn’t fit not did I have good angle to apply 121 lb-ft to it. So, I cheated and torqued the nut side and not the bolt head side. Next torque the front bushing bolts to 73.8 lb-ft. I recall they use an 18mm socket.

Now angularly align each half shaft to its flange. I had car in neutral (with key on to be able to shift gear to N). I ran battery low doing this so I should have plugged in battery tender I suppose. I plugged it in after instead when I got low battery message. Use blue Loctite on new screws and make sure to use the arc shaped clip per 2 screws. Keep spinning the wheel to get a good angle to insert each pair of screws with clip. Here is where is good to have a helper with the e brake. Spin wheel to optimal access angle for torquing the half shaft screws and have helper apply e-brake. Then torque to 51.6 lb-ft. yell to helper for remove e-brake and repeat for all 12 screws.

Put all of the stuff back on that I covered in the “Get the stuff out of the way section”. I was lucky that I discovered that my compact spare was completely flat. The valve stem had gotten a leak and I would have been in a pickle had I needed the spare. NTB put new stem on and rebalanced for free.