318ti.org forum - View Single Post - Differential parts compatibility

**cooljess76** · 12-13-2009, 07:05 AM

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.

12-13-2009, 07:05 AM	#11
cooljess76 NOBODY F's with the Jesus Join Date: Oct 2006 Location: Ventura California Posts: 7,824 iTrader: (6) Photo Gallery	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 08:03 AM.