My guess is that the Lexus IS uses the same 8" diff as the Supra MKIV (which is the same center as the trucks I showed above). The Supras came with the Torsen unit and the TRD LSD with clutches was optional/aftermarket as most TRD parts are. Total speculation based on how Toyota has carried over a good thing for years reusing their tried and true drivelines.

 

SO WHATS THE VERDICT!?!?!?! DOES THE 2IS HAVE A LSD OR NOT? I still dont know. Its weird because in a straight line there are two strips behind me. And when i burned out around 1 turn there were 2 strips, but it feels like there is still a power distribution difference between each back wheel. I am so confused.

 

Couldn't someone that has the rearend jacked up, just spin the tires. If they go different directions it's an open diif. If they go the same way it's a posi. I'm not sure if the Torsens work this way though.

 

Why is everyone bent out of shape over knowing if it had LSD or not?!? The results bear this out, why not just accept the results. I like hot dogs, but don't really want to know how they're made.

 

Have you ever heard the phrase 'lips and ***es?'

 

Actually, I think it's "snouts and rectums"

But you digress. I mean I know what the end product it, but I don't care the intimate details of the process. Referring to the LSD, everyone is concerned about this or that type of diff, but if it achieves the desired result, who cares.

 

So just put gas in and don't worry about it... Some people will be concerned about what kind of diff fluid to use. Others will want to know the different bias ratios and how it affects handling. Others might want to know which one will last longer.

There's a huge discussion going on about Sirius vs XM. It's no different. People want to compare and see what's best. They both play music.

 

This is only partially true, and the real answer only adds to the frustration. Supras with the 6 speed Getrag all had a Torsen LSD. Automatics often, but not always, did not. Some autos even had the LSD listed as a feature on the window sticker, but did not actually have them installed.

So, one model line, very limited production(<13,000 cars of all types in 5 MYs imported to the US), with two variations on just the turbo subset. The NA cars had even more variations. The only differential designed for abuse was in the 6 speed. The rest were missing internal parts.

To completely ice the cake, the Euro-spec TT Supras came with a differential cooler that was not found on any other Supras anywhere in the world.

So, is there a real answer? Does the IS have a true LSD or not?

Yes, applying the brake on the spinning wheel does act like a limited slip, and you can "cheat" an open diff by clicking the parking brake a couple of clicks if you get stuck in something loose, but that does not mean it works like a Torsen with TBR or like a clutch type LSD.

[EDIT}

OK, so I answered my own curiosity today - there is a manual for every new Scion/Toyota/Lexus called the New Car Features manual. It is intended to help techs and sales staff to understand what is new and different about a model. Typically it is published for every major revision, not every year. Since the IS350 is brand new, so is the NCF.

So the real answers are, yes there is a true Torsen LSD available as an option for the IS250 in the automatic only. Maybe not many in the US, but this manual covers US models, so only Lexus knows, but your build sticker on the driver's side door should give you a clue to what type of diff you have.

The "pretorque" differential is essentially a Phantom Grip type of affair. There is a conical washer behind each pinion gear that creates a (small) amount of friction between the pinion and the spool housing. This is similar to a clutch type LSD, but not nearly as stout or durable.

The differential cases are completely different in their mounts, so it would not seem possible to retrofit the 250 Torsen to a 350. No doubt the spools are mechanically different enough that one could not try that either - I've seen that a lot with Toyota pieces US vs. JDM like the turbos on the Supra.

Looks like we're stuck unless the aftermarket decides to fix this.

 

Wow, two different cases on the IS? I'd have never guessed they used two different ones. So people can see what these things look like, here is Auburn's cone type.

Here is Eaton's Clutch type.

I don't have a pic of a Torsen gear type handy.

 

Not the prettiest of pics, but it works.




Click here for hardcore gearhead description of Torsen products including the mathematical model used and a complete discussion about torque bias ratio.

 

Not two. Four across the 250/350 variants. 250 RWD has base and optional LSD. 250 AWD has a third type. 350 has a unique type with completely different mount points, so you could not retrofit a 250 LSD in a 350 without replacing the entire rear suspension subframe or fabbing some kind of brackets to fit the existing 350 subframe.

 

Am I the only one confused here? Could someone just list the models/configurations and what they have as a differential, if anything?

 

You're not the only one confused. The Canadian Lexus site mentions LSD with the sport package, the US site doesn't mention LSD at all.

 

From the New Car Features Manual, page CH-96:The 4GR-FSE is the 2.5 litre the 2GR-FSE is the 3.5 litre.