# 540i Diff Options



## DanB (Feb 20, 2002)

So anyone wanna buy my unused M5 3.15 LSD for $1600? DaveZ will throw it in for you!  Right Dave???

-DanB


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## DZeckhausen (Mar 11, 2003)

DanB said:


> *So anyone wanna buy my unused M5 3.15 LSD for $1600? DaveZ will throw it in for you!  Right Dave??? *


 Right! :tsk:

How much is Pacific BMW charging for that? I never got around to figuring out what sort of a deal I got on the combination of diff, driveshaft, and halfshafts. I only know that they are roughly $3000 all together.


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## JEM (May 3, 2003)

PropellerHead said:


> *Methinks the Quaife is locked. Not true LSD.  *


Uh, not quite.

There are two basic flavors of 'limited-slip' diff - speed-limiting and torque-limiting.

Spools and lockers (e.g. the old Detroit Locker) are extreme cases of speed-limiting diffs. A spool is a solid piece of steel between the axles. A ratcheting locker locks both axles together (forces them to rotate at the same speed) under power, but free-wheels when coasting.

The more common friction-type limited-slips are a speed-limiting differential. They try to control speed differences between the two rear wheels - make sure one isn't spinning too much faster than the other. Some (like the E39 M5 part) have a fixed lockup/slip ratio e.g. the "30% limited-slip", others like the GKN Viscolok in the E46 M3 and the Gerodisc clamp tighter as wheel speed differential increases and can achieve near-100% lockup. The Ferguson-type viscous differentials used in various Fords, Nissans, etc over the years act like a somewhat sloppy friction diff.

The Quaife (and other worm-gear torque-biasing diffs including the Zexel Torsen, the TrueTrac, the GoldTrak/Black Gold, and some other Japanese OEM parts) are not speed-limiting, they are torque-limiting. They'll quite happily let one wheel rotate faster than the other - basically, they work by transferring power AWAY from the wheel that offers LESS resistance, up to a certain bias limit (around 3:1 input torque difference with Quaifes, some Torsens will go higher.)

Most worm-gear diffs have a 'coffin corner' to their behavior - lift a wheel COMPLETELY off the ground, or put one on ice or other very-low-grip surface, and you get an open diff. They require some friction on both wheels to work. The Torsen T-2R and Gold Trak have friction elements in them to overcome this, but it's really only an issue on VERY stiffly-sprung cars with limited suspension travel. They also tend to produce heat, and in dedicated high-HP track cars you may need a cooler and pump.

What does all this mean for on-road behavior? The more tightly wheel speed is coupled side-to-side, the more consistent understeer you have.

So a spool produces consistent, heavy 'push' (indeed, they can prevent you from turning tightly or even break axle shafts, etc.)

A ratcheting locker produces heavy understeer under power, then gets 'loose' when you back off (can you say 'trailing-throttle oversteer'?) Some people love 'em, some like me are pretty scared of them.

Friction-type lockers produce moderate, consistent understeer.

And worm-gear torque-biasing diffs tend to offer the best turn-in and overall responsiveness but can feel 'loose' to someone used to a friction-type diff and may require backing off on the rear roll stiffness. I love 'em, and compared to an open diff they're PFM.


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## PropellerHead (Jan 3, 2002)

HOLEEE CRAP, JEM! :thumbup: :thumbup:


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## alee (Dec 19, 2001)

Best first post... EVER! :thumbup:


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## vietsb (Apr 8, 2003)

Hey JEM, do you know a good place in the Bay Area which installs Quaife's for a moderate amount of $$$ and has experience?


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## JEM (May 3, 2003)

I don't know about the 'moderate amount of money' part, but Conversion Techniques near the Oakland airport is the local Quaife dealer/shop.


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## CalvinH (Apr 5, 2003)

*Diff differences...*

JEM,
What a great explanation. I didn't know about the Quaiffe limitation before. At what point does it really operate like an open? I'm thinking about slippery roads and the like. Would it not be an issue "ever" when combined with BMW's DSC?

Thanks again for a super description, :thumbup: :thumbup: :thumbup:

CalvinH
2003 540i6


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## vietsb (Apr 8, 2003)

I think I checked w/ them back when Quaife had a sale for the E39 ATB = $1K. I should've bought one! But when I was quoted $1.2K for the install, I just couldn't justify spending more on the install than the part. Of course, I did that for my swaybars, but that was different.


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## JEM (May 3, 2003)

I'd guess 8 hours labor (3 to R&R the assembly, 3 to R&R the diff in the housing, 2 hours for stuff I haven't thought of) plus maybe $150 for seals, gaskets, and shims to be about the reasonable limit for installation, assuming reuse of the existing carrier, gears, etc.

CalvinH - aside from maybe patches of ice/slush (and in sudden split-mu conditions - one side grippy, one side icy - going 'open' might not be a bad thing) I doubt you'd ever encounter a situation where the Quaife would go 'open' on an E39.


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