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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 07-30-2020, 07:58 PM   #71
mhiscott
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Originally Posted by 86TOYO2k17 View Post
Pretty sure it’s already a 29 spline so don’t need the “fit kit”
You dont need the solid spacer, but it’s recommended uogrsde imo.
And don’t need the seal/bearing kit if your diff is low mileage can reuse. You do need a set of shims but a shop will generally have an assortment available.

M98 rear diff is the oem LSD factory 3.91 FD.
It adds a lot of labor time/expense to swap ring and pinion and crush sleeve and re-shim and set lashing/spacing vs just doing a new LSD. Could even just DIY the LSD swap is giken claims to not mess with spacing/lashing and need re-shimming.
You know, I hadn't considered that angle. That's a good idea. The M98 diff with the 3.91 or the other lexus one with the 3.7x would be a good drop in swap with only the os giken lsd to install. I figured as soon as you messed with the center cartridge you'd need to reshim everything and set the pinon depth. If that isn't the case, it would be much easier....

I guess either of the is300 diffs (the 3.9 or 3.7, lsd or non lsd) would be a good candidate for what I'm looking to do, right? I need to run some calculations to see which of the two FD ratios would be best suited to me.
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Old 07-30-2020, 08:16 PM   #72
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Originally Posted by mhiscott View Post
You know, I hadn't considered that angle. That's a good idea. The M98 diff with the 3.91 or the other lexus one with the 3.7x would be a good drop in swap with only the os giken lsd to install. I figured as soon as you messed with the center cartridge you'd need to reshim everything and set the pinon depth. If that isn't the case, it would be much easier....

I guess either of the is300 diffs (the 3.9 or 3.7, lsd or non lsd) would be a good candidate for what I'm looking to do, right? I need to run some calculations to see which of the two FD ratios would be best suited to me.
Either of the LSD ones would probably be a cheaper option. If you want 3.7 or 3.9 gears even if swapping in an lsd.
I am not sure if a non lsd one can have an lsd swapped in or not. If it can with no modification or issues i am sure they are a tad cheaper on ebay.

M85 is the 3.73 with lsd
M98 is the 3.91 with lsd
I don’t remember the non lsd part numbers off the top of my head.

4.1 fD assemblies can sell on ebay/forums for around 300$ Shipped.
If you have a 4.3 those sell A bit more maybe 500-600$. Which will help offset the cost even more.
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Old 05-07-2021, 05:02 PM   #73
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I’m necroing this thread because i cant info if there are differences between the auto m85/98 diffs. Im just looking at ebay ones they all state automatic diffs. Will those still just bolt on the frs/brz?
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Old 11-02-2021, 05:17 PM   #74
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In case anyone else needs it:

IS300 Differential Sticker:

M82 = 3.73:1 (MT) Open
M85 = 3.73:1 (MT) LSD
M96 = 3.91:1 (AT) Open
M98 = 3.91:1 (AT) LSD​
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Old 05-12-2022, 11:21 PM   #75
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Originally Posted by B T View Post
In case anyone else needs it:

IS300 Differential Sticker:

M82 = 3.73:1 (MT) Open
M85 = 3.73:1 (MT) LSD
M96 = 3.91:1 (AT) Open
M98 = 3.91:1 (AT) LSD​
These are all drop in fit correct? I'd like a 3.9 ratio to stretch the legs with my HKS supercharger a bit more, assuming I have a 4.1 ratio. 1st already goes too quick in these cars NA, 14 FRS MT for reference. But after reading all this thread, I'm not so sure what my ratio is. I would like to go with a taller gear to put 70mph less than 3000 rpm where it lives now.

And they housings are all the same? May shop for a open unit and buy a non-torsen LSD as I'm not very happy with exisiting Torsen anyway.


I think this is a better and supremely cheaper option than changing the 1-2 gears in the transmission offered on 86 sales sites.


And poking around, I stumbled on this. I heard they fit, but figured it was fab heavy so turned away. Looks like drop in units are available for those going for maximum juice.
https://www.grannasracing.com/collec...r-frs-brz-gt86

Last edited by jeepmor; 05-12-2022 at 11:37 PM.
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Old 05-13-2022, 08:37 AM   #76
B T
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@jeepmor yes, housings are pretty much identical. Your manual does have the 4.10 btw.
They are a direct swap. I'm building a 3.9 swap for my rear end right now. It's really hard to find a 3.9 with the LSD in it though. I ended up buying a rear end off of a wrecked FRS with new 3.9 gears and a rebuild kit for only $300 more than going with the IS rear end. Since you're dropping the Torsen unit, you may be best with your plan to get any 3.9 and rebuild.
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Old 05-13-2022, 07:40 PM   #77
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I was slowly coming to that conclusion after digging more. I'll have to shop around more for the right one and not just look for IS300 parts.

Just wanted to make sure the housings were identical. If I do the upgrade,
are the carriers identical as well?

I only ask as I recall some Dana44 gears from my jeep that I had to have a certain locker unit based upon the ring gear size. I don't see that case here that I know of so far according to Giken or similar.
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Old 05-14-2022, 03:48 PM   #78
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@jeepmor I ordered my parts from justdifferentials.com. Don't buy their rebuild kit though, I had to reorder half the stuff from Subaru separately due to non fitting parts.\
TV6-373-29-NG
Toyota 8", 3.73, 29 Spline, Nitro Ring & Pinion

MKTLC100-IFS - Garbage
Toyota 8" Reverse IFS Nitro Master Install Kit, 100 Series - Garbage

YOKTOYFITKIT-29
Toyota, 29 Spline Fit Kit (Includes: Pinion Flange, Pinion Seal, Pinion Nut)

SKCSTV6
Yukon Crush Sleeve Eliminator for Toyota 8"
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Old 05-20-2022, 10:53 PM   #79
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[MENTION=78328]
Yukon Crush Sleeve Eliminator for Toyota 8"
I despise crush sleeves, thanks.
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