1sFTW

I will tomorrow, isn’t the is350 carrier a lot smaller than the isf anyhow? I believe I read the carrier housing a way smaller

lobuxracer

iTrader: (2)

No the carriers fit in the exact same subframe (all 2IS have the same rear subframe as do the GS of the same time frame), so they have to be dimensionally identical. That's the easy part. The "companion flange" at the front is the same, so the driveshaft will bolt up for sure. With any good luck the axles fit - and we have enough anecdotal evidence from the past to support that. The side bearings have the same part numbers. But the spools are different part numbers. That's the vexing part. The rear cover is also unique to the IS F. No other Lexus has the same rear cover. That might be just because they put a bunch of fins on it (as well as the diff housing), which is why it would be handy to see the F Sport pics. If they are without fins, we probably have 90% of the difference between and IS F diff and an IS350 diff.

1sFTW

It definitely does not have any fins like the ISF diff, it’s the first thing I noticed when comparing the two

1sFTW

It looks like the carrier will fit. I hope the axles fit, either way, I’m going to send it and find out

Jwconeil

How do we determine if those gears will fit one of the Torsion diffs?

1sFTW

I’m not sure man. I am not planning to change the gears into the ISF carrier housing, I don’t have the tools to do it. There’s a lot of things to consider and I’m not trying to mess up tolerances and do it wrong. If I have to end up swapping gears, I will probably bring it to someone

lobuxracer

iTrader: (2)

This would be no small undertaking, except there is a strong likelihood you could use the same shims from the GS unit in the IS unit. If you can't then, indeed this turns into a major PITA because you have to measure and adjust until everything is right.

If I were retired, I'd be into this just for fun. Unfortunately, I have so little spare time I haven't even bothered to hook up the lighted door sills I bought over a year ago despite spending all the money to get the OEM wiring the same as the IS350 Luxury. Time is the enemy right now.

Jwconeil

I would just have them installed professionally. If the transmission acts normal with these gears, it will be my next mod. My goal is an NA 11 second car. I’m close, but can’t get there in Indiana. The gearing should bump me to where I need to be.

Good find.

BirgeyT1

Maybe I'm way off because I can't find any solid information but does the RC350 F-sport have a torsen LSD? If so I'm pretty sure this is the alternative that would work for a lot of people. That is, if it's a torsen LSD. 3.133 FD as well.

RC350 F-sport Rear Diff

ISFpowered

https://www.clublexus.com/forums/is-...-have-lsd.html

Seems to me like it was an added option when they were built vs all of them coming with it.

BirgeyT1

I looked at that as well but I wasn't sure if it's a torsen diff or "E-LSD".

ISFpowered

The torsen looks to be an added option which seems not a lot of them had done and if it’s not a Torsen then it’s an open diff for sure. Next thing would be if the is350 os giken lsd would fit that diff 🤔.

BirgeyT1

I'm super curious now lol

ISFpowered

Only way to confirm is calling up the dealership and seeing if LSD actually came on those carriers and checking the cars vin it came off of.

ISFpowered

Just want to fill everyone in but this made me want to literally LoL on the phone with the guy. I called the place that has all these LSD rc350 diffs and I asked them how are you guys so sure it’s a LSD and he responded “We been doing this for years we know by looking at it” my next follow up question was well how can you guys have that skill and Lexus dealerships can’t even know that without checking he responds “Well the diff has numbers on it and that’s how we know” I follow up with telling him that’s impossible because when I give those numbers to the parts department at Lexus they can’t trace it to anything specific. He comes back and tell me “we been doing this for years trust me we know”. I actually called Lexus to see what comes back for the vin that the diff came off of and let’s see if it’s really a LSD diff.