M5 Drivetrain Retrofit
I would have loved to keep the AWD system, it ALWAYS hooked up and having foul weather/ snow capability really was appealing to me but with my power levels and ride height I was having issue with the front axles and I know there was a lot of stress on the front diff and transfer case.
For the sake of simplicity and reliability I decided to convert to RWD, beefing up the drivetrain to M5 components was a logical upgrade, the M5 LSD would also help with the newly adopted traction issues.
Mechanically the retrofit was fairly straightforward but offered a couple hurdles to cross.
- Custom length driveshaft
- M5 MT output flange
- Trimming of LSD heat sink (E61 has large pull rods)
- Boring out rear LSD mount (since I used upgraded MFactory E9X mounts)
Keep in mind I already had M5 brakes and rear hubs so the axles were bolt-on for me, AFAIK they would bolt up to RWD wheel carriers but xi will need RWD/M5 hubs as the offset is much different.
Since I was going from AWD-RWD the ABS/DSC module needed to be addressed and proved to be a bit of work, this will be covered in another post.
The transmission flange had to be purchased new since anyone with an M5 trans wasn't willing to pull the flange. The other stinger was the driveshaft, I snagged a MT shaft off eBay for $175 but ended up paying $600 for the full rebuilt and lengthening, it is brand new and custom but by far the biggest expense of the conversion. I got the axles for $100/ea, LSD for a crazy good deal ($250). Axles, LSD, have ~50,000 on them. Driveshaft is "new." All new mounting hardware was ordered.
E60 M5s have the clutch-based Visco-Lok style LSD where there are 2 clutch packs on either side. The downside is there is more play so this type of LSD isn't great for drifters or the track due to the slower engagement; the upside is for straight line grip the clutch based system offers superior traction. The design is a bit flawed since the clutch packs are not serviceable so over time the slop gets worse, there can also be some grinding during full-lock turning, the only solution is some crazy expensive gear oil with a friction modifier (it costs $150 just for 1.5L of fluid to flush the 1.1L diff).
I am not a track star, I don't mind the slower engagement, and considering aftermarket LSDs are $1,000+ just for the diff itself I am happy to run the clutch setup. So far it has been working very well. My wagon is about 4,250 with me in it, I have 285/35 Hankook V12s out back and the tires hardly ever slip at 22psi and 1st limited to 18psi. The most annoying part of the LSD is slop which in combination with the toucy BMW throttle can lead to oscillation/jerking is given too much or too little throttle at low RPM. My old E39 M5 had the same issue and same style LSD.
Evan
Here is a peek inside the LSD
M5 Goodies
Axle comparison
Driveshafts
Trans Flange
Oem Diff mounts vs MFactory
Built a bushing press tool to remove the oem mounts and install the MFactory mounts which are solid rubber with a larger metal core.
Test fitting diff
Exhaust too close for comfort
E61 Pull rods wouldn't clear the heat sink, there are different M5 specific pull rods but the non-M variants seem to be superior with better mounting points so I made them work, best of both worlds IMO.
Sharpied the areas to trim, I told track the wagon so there are no thermal concerns with the smaller sink
Hacked up with an angle grinder
Hit it with a sanding flap
Not pretty but "fine" since this will live life under the car
Non-M vs Stock M5 vs Trimmed M5
