540/6 lsd

[lb540i]

Hi,

I’m sourcing parts to install an M5 LSD in my 03 540/6. I was originally just going to get a 3.15 stock M5 diff but on eBay there is currently 2 Dinan 3.45 LSD up for sale. Can’t really find much info on people putting the 3.45 setup in a 540. Any one done it? Are the Dinan ones better in anyway, other than having different ratios? They are roughly $1300ish more, trying to see if the benefits are worth the cost.

[jicaino]

For a MT I'd stick with the M5 rear ratio. The 3.46 will rip but the car will always feel "edgy". On an AT car, tho, the 3.46 works very nicely.
Just my 2 cents.

[lb540i]

Thanks for the input. I daily drive the car and unfortunately it spends a lot of time in traffic and going light to light. So the 3.15 will be more usable all around

[BimmrMeUpSnotty]

The 3.46 would get you to the next light before everybody else, but top end would get slower.

[jicaino]

Thanks for the input. I daily drive the car and unfortunately it spends a lot of time in traffic and going light to light. So the 3.15 will be more usable all around

Then the 3.15 would be the ideal choice. A tad shorter than stock. FWIW I prefer a longer final drive, but that's me. Especially if you're doing traffic, a tall rear end makes your life harder when the PP and disc are hot and grabbin'. And the lack of finesse makes you start "feathering" in more and causes premature wear.

[waters17]

Check this out. It'll give you an idea of what speed you'll be at any given gear/RPM. Just enter in the info for your specific car.

https://www.blocklayer.com/rpm-gear.aspx

Getrag 420G Gear Ratios


1: 4.227
2: 2.528
3: 1.669
4: 1.226
5: 1.000
6: 0.828

Tire size calculator for the lazy.
https://tiresize.com/calculator/


Rear Tires (assuming 18's)
265/35-18 = 25.3" diameter