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Old 12-11-2009, 03:53 AM   #1
roadrash
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Post Differential parts compatibility - DISCUSSION

It just occurred to me that one of the common questions here is "I want to swap to X differential, will it work with Y half-shafts, and Z drive shaft, etc.?"

Since I'm probably going to have some free time next week, I'd like to try to compile a table of the existing "known to work" combinations of swapped differentials etc. on the cars here. and put it in the knowledge base somewhere.

So, the first task is to come up with a list of what data needs to be gathered. How about the following...
  1. What type of transmission? (auto/manual, Getrag, ZF, etc.)
  2. Drive shaft came from what year & model car?
  3. Diff. ratio
  4. Diff. case size
  5. Diff. was taken from what year & model car?
  6. What type of diff. cover?
  7. Diff. cover was taken from what year & model car?
  8. Output flanges were from what year & model car?
  9. Half-shafts were taken from what year & model car?
  10. What modifications did you have to do?
  11. Have you had any issues with this combination?
  12. Misc. Notes

Are any of the above unnecessary?
What else needs to be added to the above list?

AFTER we get a list of all the questions that need to be asked, I'll start gathering data and put it into a table of some sort. So, hold on to your data for now.

Once I see the data, I'll have a better idea what format would work best. At the moment, I'd like to be able to create an Acrobat file (PDF) so that it can be printed out easily. But, I might also have it in a generic HTML table and/or a spreadsheet. Any thoughts on that?

JMJ

====================

This is the "listings" thread in the Knowledge Base.
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Last edited by roadrash; 12-22-2009 at 06:28 PM.
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Old 12-12-2009, 07:12 PM   #2
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I just had to deal with a similar situation & learned it the hard way so I might have enough info for you.LMK
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Old 12-12-2009, 10:01 PM   #3
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Cool... do you have any suggestions on what data that needs to be gathered? I.e., what needs to be added to and/or left out of the list of questions?
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From Page 68 of the 1997 Owners Manual: "Vehicles equipped with ASC+T remain subject to the laws of physics."
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Old 12-12-2009, 10:13 PM   #4
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I think that's a pretty good list of questions,however there's only a few choices of setups to run. Usually the output flanges & half shafts match, Z3 M diff cover or E30, plus of course the choice of small or medium case diff with desired gear ratio. I could be wrong but that's what I can sum up from my experience.
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Old 12-13-2009, 01:09 AM   #5
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Maybe each person who has done it, should just post their list of components?

Dave
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Old 12-13-2009, 01:19 AM   #6
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Well, yeah... that'll be fine as long as there is some order to it. I want to make sure the "questions" are satisfactory first, so that I don't have to go back and ask everyone for one more bit of data. :-)

Can you think of anything relevant to add to the list? ... or anything that's on the list but isn't relevant? I'm sure I'll ask that a few more times because I've never done a diff. swap so I don't have any first-hand knowledge of what is required.
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From Page 68 of the 1997 Owners Manual: "Vehicles equipped with ASC+T remain subject to the laws of physics."
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Old 12-13-2009, 01:37 AM   #7
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maybe the date of manufacture on the car and whether or not the bottom of the car had to be modified to fit the diff, I know later ti's you didn't need to do anything but I'm not sure what the cut-off date was
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Old 12-13-2009, 04:25 AM   #8
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2.93 from E30, running stock half shafts and ti flanges, stock DS

3.23 from E28, E30 cover, stock half shafts and ti flanges, stock DS
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Old 12-13-2009, 04:31 AM   #9
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Quote:
Originally Posted by pnosker View Post
2.93 from E30, running stock half shafts and ti flanges, stock DS

3.23 from E28, E30 cover, stock half shafts and ti flanges, stock DS
yup, had to do some body mods with a sledge hammer on a 9/95 build date.
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Old 12-13-2009, 04:44 AM   #10
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Hmmm... I know there will need to be a "miscellaneous notes" field, perhaps body mods would go there.

Thanks for the tip... anything else?

I probably won't be able to work on this for the next couple of days so now is a good time to work out what questions need to be asked and what data needs to be gathered. :-)
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Mods 'n' stuff: Star Spoke 43 wheels - X-Brace - Mason Engineering front strut brace - CF gauge overlay - ZHP shifter knob - Racing Dynamics cat-back - Doubled brake lights - M-tech rear spoiler
From Page 68 of the 1997 Owners Manual: "Vehicles equipped with ASC+T remain subject to the laws of physics."
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Old 12-13-2009, 06:05 AM   #11
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If you go with a medium case diff, you REALLY should use e30 halfshafts. They're beefier and fit much better. People who have ran ti halfshafts with medium case diffs have had issues ranging from halfshafts breaking under load to having to force them to fit.

e24, e28, e30(6cyl models), 2.8L Z3, MZ3 and Mcoupe's all have medium case diffs that will fit on the 318ti. 4cyl e30's came with small case diffs as did the 318ti and I think the 1.9L Z3. REGULAR E36(coupe and sedan) DIFFS WILL NOT FIT.

2.8L Z3's, MZ3's and Mcoupes have Torsen style Limited Slips while e24's, e28's, and e30's have clutch style limited slips. 5speed e24's came with 3.46 LSD's, 5speed e28's came with 3.25 LSD's and 5speed e30's came with 3.73 LSD's. Stock diff ratio for the 5 speed 318ti is a 3.45. As you know, some models came with open diffs and some came with LSD's. A thing to consider when choosing a ratio is engine RPM vs. speed. The stock 3.45 diff runs around 3800rpm @ 80mph. Lower numbers ie; 2.93, 3.25 etc, will lower the rpm's while increasing your top speed and fuel economy, but will make you slower/sluggish off the line. Higher numbers such as 3.73, 4.10, 4.44's etc, will increase your rpm's, thus lowering your top speed and fuel economy at highway speeds, but you'll take off like monster off the line. If you want to lower your rpm's at highway speeds but maintain decent power at cruising speeds, go with a 3.25 LSD. If you're happy with the Ti's stock gearing, go with a 3.46 LSD. If you're doing an engine swap, keep in mind M3's, Mcoupes and M roadsters come stock with 3.23 LSD's 318ti's came with 3.45 open and LSD's to compensate for their lack of power. BTW, there's plenty of "final drive calculators" floating around the internet. If you want to find out what your RPM's will be at certain speeds with different setups, just google "BMW final drive calculator". Here's the first one that popped up when I searched a minute ago: http://368s.com/tools/rpm Just type in your final drive ratio, enter your tire size and click calculate. 1st through 4th gear ratios may differ between the Getrag and the ZF trannys, but I think 5th gear is 1 to 1 on most BMW's.

There's two markings that will identify a LSD. First being an "S" on the identification tag. This tag is located on the differential cover, held on by one of the cover bolts. It will either say 3.xx if it's an open diff or S3.xx if it's limited slip. Another marking that will help you identify a LSD is an "S" painted on the top of the differential case. However, you won't be able to see it unless the diff is removed from the car. It often gets covered with road grime making it difficult to see. The easiest way to identify a LSD is to spin one of the output flanges. Not the input flange on the front, but one of the flanges that connects to the halfshaft. If both sides spin in the same direction, it's a LSD. If one side spins in the opposite direction, it's an open diff.

Another thing to note, if you go with an e24 or e28 diff, you'll need to purchase an e30 cover, speed sensor and output flanges in addition to the previously recommended e30 halfshafts. Reason being, e24/e28 halfshafts/output flanges have a different bolt pattern and won't work with e30 halfshafts. The output flanges pop right out, no tools required.

The 318ti uses an e30 style differential carrier, so the e24 and e28 diff covers won't fit. The e30 cover fits perfectly and is the same cover used on the 2.8L Z3 diff. MZ3's and Mcoupe's also have an e30 style cover that works, but they're usually pretty expensive due to the massive heatsink that is built into the cover. This heatsink hangs below the diff and I've yet to see one on a lowered car that isn't damaged.

The setup I'm running and I highly recommend is an e24 3.46 LSD with an e30 cover, e30 halfshafts, e30 output flanges and an e30 speed sensor. Reason being, the 3.46 LSD is really close to the stock ratio of the 318ti diff. The e30 cover fits perfectly and doesn't hang too low. The e30 halfshafts and flanges fit perfectly like it was meant to by the factory, since the medium case diff is wider than the stock 318ti small case, the shorter e30 halfshafts allow full range of movement as opposed to force-fitting the longer 318ti halfshafts which will restrict the necessary pivot range and cause excessive stress on the CV joints. And the e30 speed sensor is plug and play with the 318ti connector(at least mine was), there's different styles of connectors, you need the one that is round on one side and square on the other and it needs to be the same length as the one that originally came out of the diff that you're going to be using.

All Z3, MZ3 and Mcoupes came with LSD's. NOT ALL e24's, e28's and e30's came with LSD's, so make sure that you check for the markings or spin the output flange/shafts before purchase one.

Also, if you're installing e30 halfshafts, be sure that they came off a car with ABS. You can identify ABS halfshafts by the gear-like tooth'd ring on the outer end that mates to the wheel hub. This is called an ABS "tone ring". The ABS sensor(s) also called "pulse generators" sit about 1mm above the tone ring and receive a magnetic signal from the tone ring. Since the e30 halfshafts are larger in diameter(although shorter in length), the tone rings are also significantly larger than the 318ti tone rings. This means that you will have to "shim" your stock ABS sensors so they don't rub the tone ring and become damaged/destroyed. It's really easy to do, I just used a flat washer with a 5/8" hole. The sensor fit perfectly snug in the hole on the washer and I modified the washer with a dremel tool so the sensor would bolt back up to it's original location on the trailing arm. IIRC the washer needs to be 2.25mm thick and it should space the sensor perfectly from the tone ring on the halfshaft.

As for the drive shaft, if you're running the stock Getrag transmission, your stock 318ti driveshaft will work just fine with the medium case diff. If you're running a ZF tranny like most of us 6cyl swapped guys, you'll need to mix and match driveshafts since the ZF tranny is about 1 1/2" longer. I think the 318ti rear section with an M3 or 328 front section will work fine(again, this is only if you're running a ZF tranny).

Most of the diferentials that I mentioned have the same 4 bolt input flange as the 318ti. Some of the MZ3 and Mcoupe diffs may have a 6 bolt input flange that will need to be swapped.

That's all I know about BMW diffs, I hope I answered most of your questions If anyone feels I'm mistaken, please feel free to correct me.

Last edited by cooljess76; 12-13-2009 at 07:03 AM.
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Old 12-13-2009, 10:00 AM   #12
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Jess... do you have any additions/subtractions to the list of "data to gather" that I proposed in the first post?
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Old 12-13-2009, 07:22 PM   #13
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Quote:
Originally Posted by roadrash View Post
Jess... do you have any additions/subtractions to the list of "data to gather" that I proposed in the first post?
I think you've pretty much covered it. Perhaps weight and brand of gear oil used may be helpful. Oh yeah, year and model of the 318ti will help since certain years needed the floorboard modification.
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Old 12-14-2009, 07:48 AM   #14
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Quote:
Originally Posted by cooljess76 View Post
I think you've pretty much covered it. Perhaps weight and brand of gear oil used may be helpful.
Gotcha, added that.

Quote:
Originally Posted by cooljess76 View Post
Oh yeah, year and model of the 318ti will help since certain years needed the floorboard modification.
Good point. In my head "model" meant "year and model." I fixed that above.

OK, give me a couple of days to get in the groove of this new tour and I'll figure out how I want to gather and display the data, etc.
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From Page 68 of the 1997 Owners Manual: "Vehicles equipped with ASC+T remain subject to the laws of physics."
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Old 12-13-2009, 08:35 PM   #15
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04/1997 318ti Active
M44B19 (stock) M50B25 (installed)
Getrag 5speed
E28 3.25LSD
Motorsport Finned differential cover
Stock driveshaft
318ti Axles
lowered 3" in the rear
No issues

04/1997 318ti Active
M44B19 (stock) M50B25 (installed)
Getrag 5speed
E30 4.10LSD
Motorsport Finned differential cover
Stock driveshaft
318ti Axles
lowered 1.5" in the rear
Had issue with inner dust cover tearing open because the ti shafts are too long when lowered

07/1996 318ti Sport
M44B19 (stock) M50B25 (installed)
GM 4l30E Automatic 4speed overdrive(stock) Getrag 5speed (installed)
E30 4.10LSD
Motorsport Finned differential cover
Stock driveshaft
318ti Axles
Stock ride height, no issues
Had to modify floor board of hatch to clear a bolt for the differential cover at the top.
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