M3 diff installed in non-M Z4

[v8z4]

Last weekend I finished up the complete M3 diff/rear end install into my 2.5i/5 speed Z4.

http://forums.bimmerforums.com/forum...-LS6-T56-in-Z4

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!

[psygnosis]

How different is the Z4 M rear end from the E46 M3? I know the diff is pretty much the same, save for some cooling fins (and after reading your thread I see why :P). About how much did it cost?


Also worth noting that the six speed transmission is the same in the normal Z4 and the Z4 M.

edit: I've been playing with gearing in Forza, it looks like your car will top out in 5th at about 137 mph

[VinnieAces]

Cool mod! Glad that it all worked out for you. Enjoy the new diff

[v8z4]

Originally Posted by psygnosis

How different is the Z4 M rear end from the E46 M3? I know the diff is pretty much the same, save for some cooling fins (and after reading your thread I see why :P). About how much did it cost?


Also worth noting that the six speed transmission is the same in the normal Z4 and the Z4 M.

edit: I've been playing with gearing in Forza, it looks like your car will top out in 5th at about 137 mph

Z4M and E46M3 rear ends are identical (other than the diff cover). The Z4M cover has less cooling fins in order to clear the rear "V braces" that pass under the diff.

As I stated in the other thread, I milled the M3 cover to clear these braces:




Saved me $250 + shipping and I get to keep some extra cooling capacity.


I got lucky on the cost. A local guy (Tuscon actually but local enough) had a wrecked E46M3 he was parting out. He sold me the entire rear end (including the M3 brakes) for $700. As if that wasn't good enough, the guy even brought it to me!

Once I had the rear end, I spent another $250 or so on spherical bearings, aluminum, new wheel studs, etc. Then $200 for the drive shaft so I'd estimate around $1200 is my total cost involved in the swap. Not bad at since I see rear ends (less brakes) go for $1000-$1200 on forums/ebay.


Yeah the 6 speeds are the same, which is why guys with 6 speed cars can just buy the Z4M drive shaft and go (no drive shaft modification necessary for them..... luck bastards). For me I would still have eventually converted to the 4 bolt flange since I want to run a standard aluminum 1 piece drive shaft with my LS6 swap.

I wish my 2.5i had come with the 6 speed (like the later ones did). It sure would be nice to not be zinging along at 4K on the highway. I can live with a "top speed" of 137MPH since I hardly ever go over 80 anyways (I'm getting too old for dealing with the consequences). Besides, once I swap the T56 (with the 0.5:1 double overdrive), I'll have a theoretical 290MPH top speed.