Last weekend I finished up the complete M3 diff/rear end install into my 2.5i/5 speed Z4.
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=50644
I have been driving the car all week with the M3 diff and it's definitely quite a bit quicker. It pulls harder in every gear, it launches better, it decelerates faster (let off gas/no braking), and I think it's actually quieter than the stock Z4 diff. I'm 100% pleased with the results. The only major down side is without an overdrive (I have the 5 speed with 1:1 5th), I'm at near 4000 RPM at 80MPH. Oh well, the 2.5/5speed are not sticking around long term anyways. Also it's a bit clunky (too much back lash in the gears), but nothing unmanageable. As M3 drivers have commented, you learn to drive around the "clunk" really quickly. Now I don't even notice it.
For anyone with a 6 speed (either a 3.0i or the later 2.5i with the 6 speed), I 100% definitely recommend doing the M3 rear swap. It's not hard at all and can be done in a garage on jack stands. The 6 speed cars can use the Z4M drive shaft (I have one in my garage if anyone wants to buy it from me) and will not need to modify anything.
For anyone with a 5 speed, the swap itself is not hard but the drive shaft is a pain. With the 5 speed there is no option but to shorten the 5 speed drive shaft. The 6 speed drive shaft would be too short. You will also need to get the 4 bolt pinion flange AND a 1310 yoke flange to modify your drive shaft. It turns out the BMW friction welds the drive shaft so the rear factory BMW yoke on the flange is not salvageable. So your only option is to cut the drive shaft and convert to a standard 1310 yoke. Again, it's a pain but doable.
NOW, IF you do decide to make this conversion, KEEP YOUR STOCK REAR WHEEL SENSORS!
When I was researching for the swap, I could only find info on swapping the M3 rear into a regular E46 (325/330/etc). Everything I read said the E46 and M3 sensors were different lengths and not compatible (the E46 sensors could be spaced out to work but better to just use M3 sensors). With this in mind, I figured the Z4 sensors wouldn't work unless they were spaced out so using M3 sensors just seemed the logical solution.
After I swapped in the rear end, I immediately started having issues with my speedometer. It would "work" and give me accurate speed, however it would randomly "jump". By "jump" I mean I would be sitting perfectly still and the speedometer would "bounce" from zero to 20MPH constantly. It was almost like there was noise on the line. The doors would randomly lock/unlock, the AC would trip things out, the air bag system even thought I had been in a crash. I was totally lost.
Well, someone in another thread (the E46 CANBus thread I'm part of) mentioned that some people who had done E46-to-M3 rear end swaps had issued with the M3 wheel sensors' signals and were forced to go back to the standard E46 wheel sensor. This got me to thinking that I might as well give the original Z4 wheel sensors a shot. I knew they worked and I could easily space them out to fit as need be. Crazy thing, it turns out the M3 and Z4 wheel sensors are dimensionally identical. I can install the Z4 sensor in the M3 trailing arm, and the M3 sensor in the Z4 trailing arm. So I pulled the M3 sensors, installed the Z4 sensors, and sure enough the problem instantly went away.
SOOOOO, again IF you decide to swap the M3 rear end into something, KEEP YOUR STOCK WHEEL SENSORS!
Update: I was asked how to avoid buying a Z4M shaft (save money) and also avoid changing the pinion yoke/flange like I did. So, I suggested the following:
Start with the stock Z4 drive shaft (either 5 speed or 6 speed, whichever transmission you have), get a used M3 drive shaft (does not matter from what car). Cut the back flange off the Z4 shaft (in the straight section, stay away from the tapered/necked down area). Cut the M3 shaft (cut it long to be safe) so you have the diff end CV joint section. Make an adapter sleeve from steel bar that has steps, one end for the Z4 shaft, the other end for the M3 shaft (see picture):
The ID/OD interface needs to be around 0.005" press fit (is what I'm told by drive shaft shops and is what I used on my shaft).
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=50644
I have been driving the car all week with the M3 diff and it's definitely quite a bit quicker. It pulls harder in every gear, it launches better, it decelerates faster (let off gas/no braking), and I think it's actually quieter than the stock Z4 diff. I'm 100% pleased with the results. The only major down side is without an overdrive (I have the 5 speed with 1:1 5th), I'm at near 4000 RPM at 80MPH. Oh well, the 2.5/5speed are not sticking around long term anyways. Also it's a bit clunky (too much back lash in the gears), but nothing unmanageable. As M3 drivers have commented, you learn to drive around the "clunk" really quickly. Now I don't even notice it.
For anyone with a 6 speed (either a 3.0i or the later 2.5i with the 6 speed), I 100% definitely recommend doing the M3 rear swap. It's not hard at all and can be done in a garage on jack stands. The 6 speed cars can use the Z4M drive shaft (I have one in my garage if anyone wants to buy it from me) and will not need to modify anything.
For anyone with a 5 speed, the swap itself is not hard but the drive shaft is a pain. With the 5 speed there is no option but to shorten the 5 speed drive shaft. The 6 speed drive shaft would be too short. You will also need to get the 4 bolt pinion flange AND a 1310 yoke flange to modify your drive shaft. It turns out the BMW friction welds the drive shaft so the rear factory BMW yoke on the flange is not salvageable. So your only option is to cut the drive shaft and convert to a standard 1310 yoke. Again, it's a pain but doable.
NOW, IF you do decide to make this conversion, KEEP YOUR STOCK REAR WHEEL SENSORS!
When I was researching for the swap, I could only find info on swapping the M3 rear into a regular E46 (325/330/etc). Everything I read said the E46 and M3 sensors were different lengths and not compatible (the E46 sensors could be spaced out to work but better to just use M3 sensors). With this in mind, I figured the Z4 sensors wouldn't work unless they were spaced out so using M3 sensors just seemed the logical solution.
After I swapped in the rear end, I immediately started having issues with my speedometer. It would "work" and give me accurate speed, however it would randomly "jump". By "jump" I mean I would be sitting perfectly still and the speedometer would "bounce" from zero to 20MPH constantly. It was almost like there was noise on the line. The doors would randomly lock/unlock, the AC would trip things out, the air bag system even thought I had been in a crash. I was totally lost.
Well, someone in another thread (the E46 CANBus thread I'm part of) mentioned that some people who had done E46-to-M3 rear end swaps had issued with the M3 wheel sensors' signals and were forced to go back to the standard E46 wheel sensor. This got me to thinking that I might as well give the original Z4 wheel sensors a shot. I knew they worked and I could easily space them out to fit as need be. Crazy thing, it turns out the M3 and Z4 wheel sensors are dimensionally identical. I can install the Z4 sensor in the M3 trailing arm, and the M3 sensor in the Z4 trailing arm. So I pulled the M3 sensors, installed the Z4 sensors, and sure enough the problem instantly went away.
SOOOOO, again IF you decide to swap the M3 rear end into something, KEEP YOUR STOCK WHEEL SENSORS!
Update: I was asked how to avoid buying a Z4M shaft (save money) and also avoid changing the pinion yoke/flange like I did. So, I suggested the following:
Start with the stock Z4 drive shaft (either 5 speed or 6 speed, whichever transmission you have), get a used M3 drive shaft (does not matter from what car). Cut the back flange off the Z4 shaft (in the straight section, stay away from the tapered/necked down area). Cut the M3 shaft (cut it long to be safe) so you have the diff end CV joint section. Make an adapter sleeve from steel bar that has steps, one end for the Z4 shaft, the other end for the M3 shaft (see picture):
The ID/OD interface needs to be around 0.005" press fit (is what I'm told by drive shaft shops and is what I used on my shaft).
