3.45 Quaife LSD for E39 540i6

[mo540i6]

Hello,
Would anyone know what are the pros and cons of installing a 3.45 Quaife LSD on bone-stock E39 540i6?

[BeastPower]

I believe that your 540i 6-speed (e39) came with a 2.81 ratio (the 540i automatics already came with a non-LSD 3.15 diff). Going to a from 2.81 to 3.15 a more common selection. You can do this by either getting a new/rebuilt diff for your 540i (e39) or by getting a used M5 (e39) LSD differential (with the M5 option you will then also need to install an M5 drive-shaft and M5 rear-axles "half-shafts"). The M5 option may be similar in cost to getting a new/rebuilt diff since used diffs from places like eBay are not very expensive.

The 3.45 will provide better acceleration than the 3.15, but is going to be a little much for your car if it is primarily a street car (vs. track car), and you will be reducing your top speed and increasing the in-cabin noise, since your RPMs will be higher at all speeds. This is particularly annoying when crusing on the freeway.

If you want to just upgrade to either a 3.15 (non-LSD) or 3.45 (non-LSD) diff, then I believe that you will need to swap the differential only. However, if you want to upgrade to either a 3.15 LSD or 3.45 LSD, then you might need to also install an M5 drive-shaft and M5 rear-axles "half-shafts." However, I am not certain about this, and it is possible that you can simply purchase a new/rebuilt 540i (e39) diff that the diff builder has specified LSD internals, and that will work with your 540i (e39) drive-shaft and rear-axles "half-shafts."

The lock-up percentage is also something you can specify when you get a new/rebuilt LSD differential. The stock lock-up on the M5 (e39) is 25%, but you may want to consider going to a 40% lock-up.

We sell new/rebuilt diffs, so let us know before you buy, so that we can provide a quote.

Cheers, Daniel.

[mo540i6]

Thanks for response Dan.What is lock-up % anyway?And why you recommend going 40% rather 25%?Also, isn't it true that higher lock-up will wear your tires faster?If I get the differential,it will be LSD,I think it is a better option.
MO

[BeastPower]

Here are some details regarding the lock-up (source: http://members.aol.com/agspeed/LSD-lock.htm):

"The percentage number denotes the percentage of torque applied to the slower turning wheel from the faster turning wheel. In a straight line, both drive wheels turn at the same speed, so no limited slip action is occurring. In a turn, or when one tire is spinning more than the other (such as on snow or ice), with a limited slip differential, 25, 40, or 75 percent of the torque applied to the faster wheel is applied to the slower wheel, effectively 'limiting slip'. A higher lockup percentage will cause increased rear tire wear on the inside tire during cornering -- the tire itself will have to slip slightly to counteract the limited slip's desire to have both tires turning at the same speed. It will also increase oversteer in wet or slippery conditions, but it will also increase understeer in tight corners under dry conditions. This is simply due to the fact that with a limited slip, the drive wheels tend to want to turn at the same speed, making the car tend to want to go in a straight line. When it is slippery, however, both drive tires will tend to lose traction at the same time, increasing oversteer. The advantages are less inside wheelspin when accelerating out of a tight corner. This also translates into more horsepower to the pavement and faster autocross times -- provided that the suspension is tuned for the limited slip. The ability to accelerate out of corners without excess wheel spin can be a great advantage."

Cheers, Daniel.

[mo540i6]

Great info Dan.Many thanks.
MO