Since getting my 2007 is350 the one thing I have disliked about it is the open differential, in my opinion this was a huge missed opportunity that should have been at least an option for the car. I was worried about how the car would handle in winter, this is not my first rwd car, however it is my first without a lsd. I am getting by with winter tires but the wife has problems and I personally just dislike the compromise between either driving without traction control and spinning a tire. However it seems like my only real options could cost more than I feel the gain is worth and then I see that the is 250 guys can swap a BRZ/FR-S rear end in and it seems fairly straight forward. Question is what is the difference between the two cars that makes it doable on the is250 and not the is350. I have spent the last short while looking at pictures and trying to google the difference and it appears at a glance that it is just that the front carrier housing bushings sit wider on the is350 than the is250. Is this the only difference or have I missed something possibly more important?

If the front mounts really are the only difference I am tempted to try to fabricate a solution sometime after the weather is nice that would allow me to use a BRZ/FR-S rear end. Looking at pictures of the rear sub frame assemblies of these cars leads me to believe that making an intermediate piece would be fairly straight forward.

 

They use a different yoke flange (IS350 uses a 3-bolt with dampener, IS250 uses a 4-bolt with u-joint). The IS350 internals are larger (208mm vs. 205mm ring gear). The IS350 front mounts are wider for decreased torque placed on the rear subframe. The rear mounts are also different. The axles are shorter on the IS350. The gear ratios are also different.

If you wanted to use the 205mm diff in an IS350, you'd need to do a custom driveshaft, use the IS250 rear axles, and either swap the subframe or make custom mounts to hold it in place. The rear half of an IS250 driveshaft with the front half of an IS350 shaft may work, but without attempting it, I couldn't say for sure.

The FR-S/BRZ gearing would be well suited to an IS350 RWD though.

Jeff

 

Seeing the amount of custom work Jeff just mentioned, your best bet is to find a RARE Quaife LSD, a used '10+ IS-F Torsen LSD, an ATS Carbon LSD, or a TCD OS Giken LSD.

 

Actually it might not be much work at all depending on how hard it will be to get the drive shaft figured out. It should be fairly easy to get is250 axles and I have an idea on how id mount the mounting that would be very easy to make once I have measurements. Sure id prefer to just swap in an lsd and leave everything else be but I don't think I can justify the cost of trying to make it work with the is350 carrier. I still have some time before weather is nice enough to get under my car to know for sure if my idea will work. Until then ill be camping ebay on and off to see if maybe I can get a BRZ differential for cheap. I still need to do some more homework on the BRZ unit to make sure it would hold up reliably as the is350 weighs a bit more and makes more power.