IS300 M85/M98 rear diff - does it fit?
 

So I saw the thread about the Cusco final drive gear kit and it got me thinking that I'd like to up my final drive ratio. However, I would also like to be able to swap the diff as a unit rather than replace the internals of my stock one. I figured it might help cut down on labor costs to have a shop just install the kit with the diff already out and I could install the diff myself.

My idea was to find a compatible one in a junkyard or eBay and install a final drive kit in that, probably the 4.556 ratio offered from autofactory.jp (provided someone over there speaks English and they actually ship to the US :bellyroll:). Price point is awesome and they use Toyota parts.

Does anyone know for sure, 100%, without a doubt, that the IS300 M85/M98 differentials can just be bolted on to our cars? I've read that they're supposed to be the exact same housing but haven't found any threads with anyone actually performing the swap. I've also seen IS300 owners speculating they could use our diffs for the same purpose but without anything conclusive.

Don't have a concrete answer for you, but I ran across this craigslist post, and the guy states that the m98 is the same unit used in Fr-S and BRZ.

http://chicago.craigslist.org/chc/pts/3994245594.html

I actually kept digging and finally found this post from @Jeff Lange: http://www.ft86club.com/forums/showthread.php?p=302901

It looks like the carrier/differential assembly out of an IS300 is a direct fit for our cars. Good thing because I found a great deal on one at a local junkyard. :D Now I just need to see if I can get the gear kit and required pinion seal through amayama or autofactory and I'm good to go!

I sure hope it turns out to bolt in. I'm eying up the m85 3.73 set out of a manual car....

It's definitely a completely bolt-in affair with a differential assembly from an IS300 or IS250.

:)

Jeff

This looks like a nice option if it's perfect fit.

soooo. is it? :)

what is the stock ratio? and has anyone done this and can say its a 100% direct fit?

Best wait until someone actually does it themselves before rushing out and potentially wasting money.

For the record, I contacted a local shop to get an estimate on doing a final drive gear swap. As an alternative, they offered to sell me a differential that would fit... in a 3.91 final drive ratio. Hmmmm, that sounds like a familiar number... what diffs have we talked about that have that ratio already installed... :D

Great info--this forum is awesome.

Please let us know how this goes. What is the stock ratio? Does it have a similar lsd?

Stock ratio is 4.10:1.
IS300 AT is 3.91:1.
IS300 MT is 3.73:1.

Not all IS300's have LSD, so you'll want to make sure before buying one unless all you want is the ring and pinion.

Jeff

Or just swap our LSD into that case. I'm on the look out for a 3.73 third then.