BRX/FRS diff the same as IS300? - Page 2 - Lexus IS Forum
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post #16 of 184 (permalink) Old 01-20-2015, 11:50 PM
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Nice sheet you made there reklips, anybody know will our axle stubs fit into the frs differential without modification? I will buy one if they can
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post #17 of 184 (permalink) Old 01-21-2015, 09:22 PM
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While this isn't empirical data, I've read that the stub shafts simply press into the BRZ/FRS rear diff, as there are a few of those guys who have simply removed OEM IS300 LSD diffs, popped out the stub shafts, and installed our diff into their cars.
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post #18 of 184 (permalink) Old 01-22-2015, 04:59 AM Thread Starter
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While this isn't empirical data, I've read that the stub shafts simply press into the BRZ/FRS rear diff, as there are a few of those guys who have simply removed OEM IS300 LSD diffs, popped out the stub shafts, and installed our diff into their cars.
I was thinking this might be a nice source of LSD diffs for our cars. Maybe mix and match the ring gears. That would be the next step, get one of these diffs and see if the LSD will bolt into our housings. I think they will but like you, I don't know for sure until it's done once.
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post #19 of 184 (permalink) Old 01-23-2015, 06:16 AM
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I'm going to try it. Hopefully mystateside mechanic can take some pics, I'm having my car in New Mexico prepped to send over to me here in the UAE...
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post #20 of 184 (permalink) Old 01-24-2015, 07:01 PM
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cool matt k i am going to try it as well...let me know how it goes when u decide to do it
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post #21 of 184 (permalink) Old 01-24-2015, 07:17 PM
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Hasn't been done before to my knowledge. In theory they are compatible yet not proven. LSD would be the only benefit, however. Gearing is another story.

"There's nothing like waiting and getting exactly what you want."
-Hiral
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post #22 of 184 (permalink) Old 01-25-2015, 12:50 AM
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Going to 4.11 gears from 3.91 gears is a very minor bump, which will allow for better acceleration, with a minor difference (~200 rpm) between a given speed compared between the prior and latter setup. Not enough to dissuade me...the IS has always been down on low end power compared to other cars, and a loss of 5mph or so top speed just isn't enough to say it isn't worth it to most people. Careful tire selection can correct the speedometer difference, if you care to do the math.
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post #23 of 184 (permalink) Old 01-25-2015, 03:58 AM Thread Starter
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On the 01's it would have no impact on the reported speed because they read speed off the ABS. I'm not sure on automatic IS's of later years.
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post #24 of 184 (permalink) Old 01-28-2015, 02:57 AM
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I'm going to try on my 2002. I just bought a BR-Z rear end on EBay. I'll need to do the math & see how far off my speedo will be going from 3.91 to 4.1 gears, with 245-40-17's. I'll let everyone know how it works out...
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post #25 of 184 (permalink) Old 01-28-2015, 08:45 AM
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Quote:
Originally Posted by reklipz View Post
Doh, forgot the link:

https://docs.google.com/spreadsheets...it?usp=sharing

The tire radius is in millimeters, use this calculator and convert the Tire+Radius measurement: U.S And Metric Tire Size Information Calculator
You should be able to copy that first sheet, plug in your numbers (change one of the diffs to be the BRZ one, same with the tire size) and see the results.
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post #26 of 184 (permalink) Old 02-05-2015, 10:41 AM
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Any updates Matt? I am waiting to see what happens heheh i will do the same if urs works out!!!
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post #27 of 184 (permalink) Old 02-05-2015, 08:32 PM
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My diff arrived yesterday. My car is getting a bunch of work done, this is on the list of to do items...I'll post pics and info as they come.
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post #28 of 184 (permalink) Old 02-05-2015, 11:38 PM
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Originally Posted by Matt K View Post
My diff arrived yesterday. My car is getting a bunch of work done, this is on the list of to do items...I'll post pics and info as they come.
I added your setup as the green configuration on the main sheet: using 4.10 brz diff ratio and 313.944 mm tire radius, with w55 trans. Not sure it's really helpful beyond what you get just thinking about it in your case, but now you can compare different trans, which is the meat of the calc.

I'm curious what the outcome is for sure, glad someone is taking this one on.
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post #29 of 184 (permalink) Old 02-05-2015, 11:59 PM
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Quote:
Originally Posted by reklipz View Post
I added your setup as the green configuration on the main sheet: using 4.10 brz diff ratio and 313.944 mm tire radius, with w55 trans. Not sure it's really helpful beyond what you get just thinking about it in your case, but now you can compare different trans, which is the meat of the calc.

I'm curious what the outcome is for sure, glad someone is taking this one on.
Thanks, I'm still using the old A650 slush box though, my wife doesn't want to row the gears...that's what I've got my Mustang for.
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post #30 of 184 (permalink) Old 02-18-2015, 10:29 PM
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Well, the FR-S diff is in. No modifications were required, very straightforward swap. The only (minor) issue was the need to install 1/2" spacers under the front bolts in the new diff, as it's just a little shorter in the threaded area. I'll upload some pics here once photobucket stops crashing on me...

The small difference in gearing means I'll be approximately 200 rpm higher at any given speed. I can make up for this by going slightly larger in tire diameter if needed...
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