Split

This is all taken from www.is350forums.com
I'm trying to figure out if the canadian model IS350 sport has an actual Limited Slip Differential, or if it just has the "Pre-Torque” semi-LSD.

So I noticed on the canadian website, the IS350 Sport Package has a Limited Slip Differential, and on the American website there is no mention of an LSD. Is there a Limited Slip Diff on the American model IS350 Sport?

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I found this on this website: https://www.clublexus.com/index.php/...view/7475/1/10

"Power for the 2GR-FSE 3.5L V6 is transferred to the rear wheels via the “Pre-Torque” semi-LSD found exclusively on the IS350"


And this on this website: http://my.is/forums/showthread.php?t=265873

"A keen eye will notice there is no Torsen LSD available. Instead, the IS350 comes with a "pre-torque" semi-LSD."

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so that leaves me with 2 questions:
1) is this Pre-Torque” semi-LSD only available on the sport package, or all IS350's?
2) is the canadian website wrong, and where it says "Limited Slip Differential" it should say Pre-Torque” semi-LSD?
a limited slip differential is pretty important to me, so if the canadian model has it, i'm not going to bring the car up from the states, i'm just going to buy it locally.

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I'm pretty sure it comes with all the IS350's. And I'm pretty sure the canadian LSD is the same thing as the american semi-LSD, they just named it something different.

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So my question is: does the canadian model IS350 sport have an actual Limited Slip Differential, or is it just the "Pre-Torque” semi-LSD?

jcreech

ive seen this question asked 100 times...still ive yet to see an answer.

RCFormante

iTrader: (1)

Its the same as the US...they just reword it a little bit.

monkeyfarm

I have zero data to back this up, but I can't for the life of me imagine any reason that Lexus of Japan would figure that the Canadiennes just HAVE to have an LSD while the yanks don't. It just doesn't make a lot of sense to me from a logistics/engineering standpoint.

My bet is either:

- all 350's have the same diff
or
- all 350's have the same diff, with the exception of the sport pkg cars, which have a semi-LSD (pre-torque or whatevery they want to call it).

Here's a nice informal test:

- someone with a sport pkg car, go do a burnout. Do you get both tires to light up?
- someone do the same thing in a non-sport car and report your findings

RCFormante

iTrader: (1)

I did this awhile ago. No sport or lux pkg...both tires spin and two tire marks on the ground.

uschardcor

canada is dumb and advertises false.

they both have a pre-torque LSD

mike714

So what is a pre-torque semi-LSD and how is it different from any other LSD?

monkeyfarm

I'm daft. Lexus basically fudged the name of what I'm reasonably sure is just their version of a Torsen differential.

Here's the short version on how the torsen diff works:

However, since the LSD in the Lexus DOES have fluid, it's obviously NOT a pure torsen diff. Perhaps a hybrid, perhaps not.

You can read about other types of diffs here. As for exactly what's in the Lex... not really sure.

http://auto.howstuffworks.com/differential.htm

tigmd99

I don't know about Lexus cars, but Toyota has used the term, "limited-slip differential" or "automatic LSD" in many of their SUV brochures to descibe TRACTION CONTROL. No more and no less.

spwolf

yep, it should be traction control which acts as LSD...

Bichon

That's my guess, too. All you need to get LSD functionality (i.e. traction control) on an ABS equipped car is a little extra software. When one wheel starts spinning, the computer applies the brakes to just that one wheel, which transfers torque to the other side.

mike714

They're not even remotely the same thing. My previous car was an automatic Acura CL with VSA, Acura's version of VDIM back in 2001. I sold it to get the manual version of the same car except it has an LSD and no VSA or any other electronic traction control system. There's a world of difference between the two systems and how they handle. When the VSA kicked in, its response was always to kill the throttle and hit the brakes. When the LSD kicks in it, its like the front wheels (FWD) instantly grow spikes and dig into the pavement. It also effectively nullified the FWD understeer tendency too. So much so that I almost hit the center divider making a left turn the first time it happened. VSA also wouldn't let me spin the tires for more than a chirp while the LSD will let me spin them easily and keep the car going straight even if one wheel runs through a puddle.

larsdenner

I can help out here as I do a lot of 4wheeling and have been around this stuff for a while. An open differential allows the wheels to spin freely at different speeds so that when going around a corner the inside wheel is allowed to spin slower than the outside since it has a shorter distance to travel. This is called differentiation. Without it the tires would scrub, loose some traction the car wouldn't corner as well.

The disadvantage is that if one tire has less traction, the torque of the engine will seek the easiest route and cause the tire to spin out of control. The old one black mark syndrome. The Lexus has Traction control that senses this inequity and will brake the spinning wheel to bring them in line. If both are spinning wildly as compared to the front tires it will back the power off for you.

Now on to limited slip differentials. LSD's will bind the two wheels together with a certain amount of force so they spin the same speed. The more power from the engine, the harder the binding force. LSD's are rated in bias. A 3:1 bias means the LSD can send 3 times the force to one tire as the other, if necessary. This allows power to still get to the tire with more traction. Unfortunately you can see that if one tire has zero traction, 3 * 0 = 0 and you still go nowhere.

How LSD's perform this function varies. Torsen, an acronym for Torque Sensing, uses the effect of gearing to perform bias. A good analogy would be to think of how hard it is to pedal a bike in 10th gear at slow speed vs first gear. A Torsen allows differentiation or movement just like going in tenth gear but makes if difficult to achieve when you apply high power. Another type of differential reffered by Lexus as a pretorqued is probably a clutch type LSD. When high power is applied by the engine the clutches or cones are forced together disallowing differentiation. Under enough back pressure from the wheels they will differentiate though. The clutches or cones will have heavy springs that preload or pretorque them providing a bias that is built in. Eventualy the clutches wear out. Sometimes this type of LSD requires special axle fluid so that the clutches don't chatter.

So that's the basics on LSD's. Just two different ways to do the same thing. Here is a picture of two open diffs. One is an 8" out of the rear of my 4Runner and the other is the 7.5" out of the front. It's easy to see what's going on in the 7.5" since it has openings. The internal spider gears are tied to the axles which go to the wheels. They can pivot to allow the shafts to spin at different speeds. The entire housing spins and is driven by a ring (or crown) gear which isn't shown here because it is installed on my locking diff instead.


4Wheelers use something more extreme known as an automatic locking differential. Offroad, a tire will often come off the ground and have zero traction and hence an LSD can't help because it can only bias so much power but many wheelers do use them. They are better than open. A locking diff, though, will never allow a wheel to spin slower than the input from the engine (actually the crown wheel) however a wheel can spin or ratchet faster than the engine to allow differentiation. This way there is always power going to the ground. The mechanism is a bit more complicated as it also doesn't allow the system to coast freely but you get the idea. There are also devices called spools that never allow differentiation. The wheels always spin at the same speed. This isn't so good on the pavement as the vehicle handles poorly, doesn't turn as well and wear out tires quickly. They are mostly used for off road only vehicles and are simple and strong. A nice option is called the manual locking differential. It behaves like an open normal diff but when you loose traction you can flip a switch and the diff will lock to a spool configuration. This is achieved with either an electromechanical, pneumatic or cable operated system. I happen to have air operated locking differentials installed in my 4Runner.

Here is an article I wrote some years ago on the subject if you are interested beyond http://www.larsdennert.com/traction

And here is a write up I did for an online magazine some years ago on installation of a differential http://www.4x4wire.com/toyota/4Runne...ifs_airlocker/

skorpio

Now we need one of us to open the diff and have an answer once for all Any takers? or we could ask the service.....

regards, Bart.

jack278

As long as I can install an aftermarkert 1.5way LSD on the IS, I'll be happy. Most OEM LSDs are too slow anyway.