LSD Differential

[Speedfreak]

I did a search and there's a lot out there. But who has actually done an LSD and ratio change on a 540i? I need some first hand opinions. Anyone with an auto?

Thanks, Pat

[Skipper5]

i've read a lot of the guys were doing a 3.15 LSD from Quaife (sp?) with great results. it gives you the added kick without taking away driveability at freeway speeds. i say go for it :)

[Speedfreak]

I'm running a 3.15 now as I have a 540i sport auto. I wonder if going to a 3.38 or a 3.46 LSD is worth the $3000.00 I'd have in it.
Pat

[marinakorp]

I'm running a 3.15 now as I have a 540i sport auto. I wonder if going to a 3.38 or a 3.46 LSD is worth the $3000.00 I'd have in it.
Pat


1 - the LSD is GREAT if you live in a climate that gets snow

2 - the 346 will give you more off the line punch, at a cost to top end and gas mileage

[Speedfreak]

The LSD might be nice when going with a 3.46 to handle the additional torque going to the wheels.

I would lean more towards the 3.38 but with only about a 5% change I dont know if the improvement is worth the money. I would hate to go cheap with a non-LSD 3.38 and still need LSD. :confused

[MaloventEvil]

yep. a 3.38 isnt worth the money. but for me it is :D that would be a huge change from my stock 2.86

[Speedfreak]

Yeah, I'll have to think about it. I think a 3.46 would really bring my 540 to life. It would only increase my cruise RPMs about 10%. That's only about 210 RPM at 65 - a little more at 80.

[Lscman]

My substantial personal experience with the sister Torsen (100K+ mi) worries me about Quaiffe. These units are VERY similar designs. If the inside tire lifts, this type of differential will lose almost all of it's cross-torque bias and begin spinning the inside wheel like an open diff. Once the tire breaks loose, it will not regain grip. It will act like a burned out OEM posi with scorched clutchs...one that needs rebuilt. Most folks will be disappointed. This undesireable characteristic is most noticeable with topheavy sedans with moderate or narrow track width. A Corvette does not fit in this category...but a 5 series with a 150lb moonroof system and V8 surely does.

The Quaiffe should be great for equalizing traction in snow, rain and drag racing (low lateral G's). That said, it may feel like an open diff for autocross or sharp, road racing turns where high lateral G's are generated & the inside tire gets real light from a big swaybar. Cars with genuine race springs with higher rear rates and modest bars may not have this issue. Cars that keep the inside tire planted and exhibit good squat on corner exit will love a Quaiffe...like a Ground Control M3 with 500lb springs and stockish swaybar. I don't know of many 5's in this category though.

Just a warning for folks considering this upgrade.

[Speedfreak]

That doesn't sound like something I want to happen. :eek

[Lscman]

Then your only recourse is to install a conventional clutch-type heavy duty posi that was employed in the E39 M5. It'll set you back around $6K by the time you retrofit it, since the 540i halfshafts need swapped out for M5 units and these diffs are costly. Trying to find one in a salvage yard is an impossible dream.

Moral of the story is probably...stick with your open diff.

[SehrSchnell]

I'll be switching my 3.46 to a 3.91 in some days to come. I may have the 3.46 for sale later.

[Sean@quaife]

I would have to disagree with these Quaife experts. That is not how our ATB's work. They are much more complex than that and stronger than your typical clutch style diffs.

[Lscman]

OK, educate me........


I would have to disagree with these Quaife experts.

Quaife is not a significant improvement or redesign of the Gleason-Torsen. It has been altered to avoid patent infringements. The helical and invex gears used in these competing diff's produce the exact same ATB effect. Even methods used to generate a bit of preload friction are similar. Both behave identically under conditions where traction goes away on one wheel. I'm not sure what you're having to disagreeing with here, so please explain.


That is not how our ATB's work.

Not how it works? Aside from spelling errors, please point out & correct any erroneous info being offered for consideration. Exactly how much torque does a Quaife apply to the road when a tire lifts?


They are much more complex than that....

More complex than what, a Torsen? That's like saying a Panasonic VCR is much more complex than a Sony.


......and stronger than your typical clutch style diffs.

Stronger than which E39 differential? Is the torque bias greater than 30%? What about when you lift one wheel and the torque applied to the tire with traction approaches zero? Under these same conditions, the OEM clutch assembly continues to provide substantial bias...on the order of 100 lb-ft! Are you actually claiming the tiny E39 Quaife is stronger than a typical OEM E39 clutch differential (M5) that offers useful torque bias under extreme one-wheel traction conditions?

Stronger, better, different.....I'm anxious to hear clarification. Maybe you are you comparing it to the stock 540i differential? I'm not sure.

If someone were interested, where could they purchase Quaife E39 540i differentials at Quaife UK's full suggested retail price of £660 ($1100 US)?

Thanks for any replies.

[Tahoe M3]

This is a fascinating discussion and I'm anxious to see it continue as it is something I am quite interested in.


If the inside tire lifts, this type of differential will lose almost all of it's cross-torque bias and begin spinning the inside wheel like an open diff. Once the tire breaks loose, it will not regain grip. It will act like a burned out OEM posi with scorched clutchs...one that needs rebuilt...

I am not challenging you here, just trying to educate myself.
I don't understand the difference between loosing traction on snow or rain vs loosing traction by lifting a wheel. (Something I am quite unlikely to do in a 540 even at a driving school.)


The Quaiffe should be great for equalizing traction in snow, rain and drag racing (low lateral G's)...

[Lscman]

This is a fascinating discussion and I'm anxious to see it continue as it is something I am quite interested in. I don't understand the difference between loosing traction on snow or rain vs loosing traction by lifting a wheel. (Something I am quite unlikely to do in a 540 even at a driving school.)

Lifting of a wheel is not actually required...you simply need to "lighten it" a lot & then squeeze the throttle hard. This occurs quite often...like making a hard 90 degree turn into a side street in second gear, while going fast enough to hear some front tire squealing. Under this condition, your RPM is likely in it's sweetspot. What happens is the inside rear tire will break loose with an ATB LSD (Torsen or Quaife), as you apply the throttle hard on corner exit.... much like an open diff. If DSC is ON, the ATB will function better.


ATB function is good (under poor traction conditions) with Torsen and Quaiffe for several reasons. Incidently, this is why Hummers come with Torsen, and FYI, quite a few other serious off-road vehicles have similar ATB LSD's as OEM. When you lose traction in snow, the torque levels are much lower. Another reason ATB works real good on wet and snow is because the driver does not apply full throttle....and because high cornering forces are not being applied that cause chassis tilt. Lateral G loading causes the rear swaybar to lighten the inner wheel and apply more downforce to the outer tire. Of course weight transfer and spring characteristics add to the tire loading differential across the chassis. Lateral G's greatly aggravate the traction difference between the right and left side..yet the differential's torque transfer capabilities do not improve under this condition. At some point, engine torque applied will exceed the torque transfer limits. This is also why straight-line traction is good with a Torsen or Quaife ATB and why brake-torquing maneuvers improve ATB function. It fakes the diff into thinking the wheel has grip and this allows the invex or helix gears to do their thing (transfer torque). Under these conditions, the instantaneous torque bias provided is high.

Hope this makes sense.

[540man]

I did a search and there's a lot out there. But who has actually done an LSD and ratio change on a 540i? I need some first hand opinions. Anyone with an auto?

Thanks, Pat

I have done the diff swap on my auto 540. Went from the stock 2.81 to a 3.15 LSD. I also have bigger rubber (265/40-17") on the rear.
Biggest difference is the punch at low speed. As you know, the stock diff makes the car a bit of a slug off the line until you get some RPM on the dial.
The 3.15 make this much better. As I drive mostly in the city, I am very happy with the results. The car is much more enjoyable to drive in town. The engine RPM at hi-way speed is of course higher. It is not a lot, maybe 200-300 rpm at legal speeds, but fuel mileage does suffer. Maybe 2-3 mpg on the hi-way. In the city, probably no difference. Maybe even better with the 3.15 as I am in the throttle less to get underway.

With the stock gears, the car would pull right to 150 mph, then big brother stepped in. I have not done a top speed run with the new gears yet, but have been to 230kph (about 135 mph) and there was lots of rpm left, so I suspect no issue getting to the 150 mph cutoff.
I have had no problems with the LSD interfering with the traction control functions. With the trac control off, the car acts like any car with an LSD : push the go pedal hard enough around a corner and you will slide its butt out into a drift situation.
I do not drive the car in the winter, so I cannot comment on the snow/ice performance.
I do not track the car, so I cannot comment on the inside rear tire lift issues.
All in all, for the $$ I spent, I am very happy with the 3.15 swap.

[Lscman]

I concur with 540man's comments.

Another thing to consider is chassis setup. A stock-ish E39 V8 tends to plow or push because the rear suspension is quite compliant. Under these conditions (soft rear), an ATB works well. Problems start when you tighten the rear end up to remove understeer via a bigger swaybar, progressive springs or stiffer linear springs. You will discover an ATB LSD has much more difficulty putting the power to the pavement in corners with most E39 performance-tuned setups. Making the rear tires work harder in corners simply means the inside tire will get lighter. Some workarounds are possible, but they involve very careful coilover/swaybar tuning. The E39 crowd has not explored this issue yet...M3 track enthusiasts have. Some M3 racers don't even run a rear bar with high spring rates...& they'd surely hook up well with a Quaife, but the necessary spring rates will dislodge vertibrae of rear passengers. Not what most folks want in a 4dr sedan.

Again, the ATB LSD's have many plusses, & compared to an open diff, no minuses except for cost. The adverse weather & mud functionality is "remarkable", even in a 2WD RWD sedan. It's almost like converting to FWD in snow. I don't mean to minimize Quaife effectiveness, but the bang for the buck is kinda low. I modify my cars based largely upon this quotient. This might not matter to some folks, I don't know. A gear ratio change will offer the "Lion's share" of the bang for those folks interested in better low speed acceleration. Many ponycar enthusiasts have a different opinion about ATB's...mostly because they can install an ATB posi for $400 and it lasts FOREVER & a set of deeper gears can be added for $180. Not much buck spent there.

Sorry for babbling...hope this helps.

[5mall5nail5]

I'll be switching my 3.46 to a 3.91 in some days to come. I may have the 3.46 for sale later.


Let me know

[mformal]

i recently got a 540a and was looking for someone who specializes in rear end gearing and found
www.performancegearing.com
they have a good sight although check with bimmerfly.com for references

[Lscman]

An excellent option for the 540i application, of course. The conventional LSD clutches are my pick for the 540i. I've heard good things about the Salisbury design, although it's very new. I'm hoping it's affordable...been eyeing it for a while.