Swap 188mm auto pumpkin for 215mm? Diff cover options?

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
For those who don't know, there are two sizes of ring and pinion for the 6AT, 188mm and 215mm. A later post explains the differences between models, but most people with an auto have the smaller, 188mm which I'm told also has thinner axles. Currently I have the 188mm, but I'd like to convert while I am doing my LSD so I bought a 215mm auto pumpkin out of a 2006 production auto 335i. After asking, Jesse(@Darklabs ) informed me that the 188mm axles and driveshaft will fit in the 215mm differential, so this may be a direct swap.

The reason for doing this is the potential strength benefit as well as being able to add a differential cover with fins and a drain plug, which mine does not have.

As far as differential cover options, excluding the $800 cover made by VAC, there is the M3 diff cover p/n: 33112283010 which has no fill/drain hole and is quite pricey. And my current favorite, the E63 650i finned cover which fits the big diff. Keep in mind, if you're auto, you'll need to either have the 215mm differential, convert from the 188mm diff like I'm trying to do, or see if the 188mm finned diff cover mentioned at the bottom of this post will fit. Please keep in mind, I don't know how any of these covers work with diff lock down kits. Here is a picture from @PC Racing

wGsLWt0.png


This cover has a 1.25" lower clearance and requires a spacer and longer bolt to prevent it from being pulled out of the subframe when tightned, since it is not as thick as the stock cover. You may also need to trim a few fins so the exhaust does not interfere, just depending on what exhaust you have. @PC Racing is making me a 15.5mm spacer which I'll be testing and see if it works.

What you'll need:

650i Cover: 33117519661
M14X1,5X130 Grade 8.8 Bolt: 07119914854 (Or the recommended grade 10.9 Bellmetric Bolt BH 14 X 1.5 X 130)
M10x25 hex bolt: 33117521292
And a spacer that needs machined: @PC Racing can make them, see pics of it Here

Here are some comments from Pig Farmer on making the spacer:
I realize this thread is kind of a work in process and needs to be cleaned up with final measurements once the install is complete. The spacer I made is 1-1/4" OD, 9/16" ID and 15.5mm long. I cut the spacer from a piece of aluminum round stock (1-1/4" in diameter). If I were to do it again, I would use 1-3/8" round stock.

An alternative method would be to get a 5/8" thick piece of aluminum plate, and use a 1-1/2" hole saw to cut out a core. I tried this with a 1/8" think piece of aluminum plate and the core was just under 1-3/8" in diameter. Then drill out the center with a 9/16" bit. This would result in a spacer 5/8" or 15.875mm long. The difference between 15.5mm and 15.875mm is about the same as 4 sheets of paper. This method requires a pretty sharp hole saw, lots oil/WD-40, and a pretty beefy drill press.
---------------
As for the auto guys with the 188mm diff, there is also another part number: 33117516280
This apparently fits the 188mm 128i with a 15mm spacer, but I don't know if there is any compatibility with the '35i small 188mm diff.

This photo is from Bimmer-Bob
Oc3M03G.png
 
  • 2Like
Reactions: _mpreza and AzNdevil

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
Thanks to @BMWJunkie for these great comparison shots. It doesn't seem that the axles are much different. The 188 drive shaft is longer and appears to be thinner near the center section taper.

17855389_10212955486185975_4346157758908962533_o.jpg
17814682_10212955483385905_438418442520862604_o.jpg
17880267_10212955487226001_6396985905454512954_o.jpg

FB_IMG_1492044490768.jpg
 

bradsm87

Corporal
Dec 15, 2016
162
So is the 215 diff a 100% straight swap in replacement for the 188 diff? It looks like the driveshaft flanges are more spaced out from the housing on the 188. Is the distance from flange to flange the same between both diff sizes and also the distance between the said shaft centreline and the front of the diff itself?
 

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
So side shafts are the same but the tailshaft from the centre bearing backward is shorter to allow for the longer diff?
I don't know much more than can be deduced from the images provided. I'm only told that the swap has been done by @Darklabs on multiple occassions as a direct swap. There are small differences in the parts but apparently they work together. If you just want a finned cover, I provided a part number for a 188mm cover which has one, you could try that out.
 

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
Here are some pics of my MFactory 215mm 3.46 diff. I got new bearings and my lockdown brace and spacer from @PC Racing showed up also!

IMG_20170501_130331.jpg IMG_20170501_130502.jpg IMG_20170501_151337_01.jpg

I put in my order for the diff cover and bolts, they should be here by wednesday.
 

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
My finned diff cover showed up, it weights just over five pounds according to my highly inaccurate scale.
IMG_20170510_153016.jpg
 

doublespaces

Administrator
Oct 18, 2016
7,609
AZ
Unfortunately the finned diff cover will not fit with a convertible brace in the way as you can see so I had to install the 215k pumpkin with the normal cover.

BTW: I'm selling the cover and one-off lockdown brace with the 15.5mm spacer necessary to fit. It is unlikely someone other than @PC Racing will make another brace because you'd need all these things in hand before you go to town fabricating again.

The 215k is aprox 15mm longer at the driveshaft and 12mm wider.
received_10203123244360191.jpeg
received_10203123245040208.jpeg
received_10203123245160211.jpeg
received_10203123246280239.jpeg
received_10203123274240938.jpeg
received_10203123303561671.jpeg
received_10203123304921705.jpeg
 

frontside0815

Corporal
Nov 9, 2016
126
Germany
Just FYI:

I swapped from a 215 Diff to a 188 Diff, without changing anything!
The 188 is a Little bit shorter, like seen on the Pictures, but you can pull the driveshaft a Little bit.
At first i wasn´t sure if that is working, but i had 2 track day´s and everything works fine, so you can say it´s no Problem.
 

DirtKurt

Specialist
Free Vendor
Nov 5, 2016
86
NH
Just FYI:

I swapped from a 215 Diff to a 188 Diff, without changing anything!
The 188 is a Little bit shorter, like seen on the Pictures, but you can pull the driveshaft a Little bit.
At first i wasn´t sure if that is working, but i had 2 track day´s and everything works fine, so you can say it´s no Problem.
So you were able to swap to a large pumpkin directly without changing any other parts? This is very interesting if so.

@sirdaft1 I think this answers your question
 
  • 1Like
Reactions: doublespaces

Create an account or login to comment

You must be a member in order to leave a comment

Create account

Create an account on our community. It's easy!

Log in

Already have an account? Log in here.

Top