Replacing/Upgrading Transmission
 

Hey guys, I'm new here and I got this car back in March (2015 FR-S). This is the first car that I've owned where I want to do modifications. I've owned bikes and done quite a bit of mechanical work on those, but this is another monster entirely.

I'm looking to install a supercharger in the near future (year or so), but I want to make sure my transmission is where it needs to be before I do that. I've heard a lot of good things about Jack's Transmission. I was told that if I'm going to be doing any kind of boost, that I may want to look into a performance rebuild as well as WPC treatment and CF synchros.

I plan on buying a used transmission from eBay and shipping it to Jack's so I'm not without my car while I wait on the transmission to be rebuild. Is there a specific year that I should be looking for? And obviously I should try and find low mileage/undamaged. I'll be pulling the transmission myself with the oversight of an experienced mechanic. I want to make sure I don't miss anything. Can you guys give me suggestions on what other parts I may want to replace/look into while I have the transmission pulled?

You definitely don't need to do anything to your transmission for a supercharger :)

Gotcha, that's not the only reason I'm doing a rebuild. I'd like the added reliability and smooth shifting that comes along with it.

I think the previous owner either didn't know how to shift or was terribly rough because I am starting to have issues with 4th and 5th gear. I was told that it's a synchro issue and would require a rebuild. I figure if I'm going to rebuild it, I might as well make it bulletproof while I'm at it. Especially since I plan on adding more power.

Understandable if you need a rebuild, but you're not going to improve the torque capacity or make the trans bulletproof with your current plans. Excessive power tends to destroy the actual gears, which is expensive to remedy and most end up converting to a different trans. As noted, you "should" be fine with a typical supercharger build though.

To be honest, a transmission that was assembled at the factory will be more reliable than one that has been torn down and rebuilt. That's just my opinion though.

I would try changing the transmission fluid a few times with something like the Motul fluid. I used to have a persistent 4th gear grind if I shifted into it at high RPM. Changing the fluid every 500 miles 3-4 times ( expensive, I know) fixed this completely. $170 in fluid is cheaper than a trans rebuilt though! If it makes you feel better, my car is turbo and my transmission has been perfect.

Okay, I was under the impression that a performance rebuild with gear treatment (WPC in this case) would increase reliability, decrease friction, and increase durability. So the only way to increase that (torque capacity) would be with a completely different trans?

Also, if I'm fine with a typical SC build, and I just need the trans rebuilt, what will the performance rebuild with the options listed above (WPC treatement, CF synchros) do for me?

I've changed the fluid 4 times now and I'm still getting 4th and 5th gear grind at high RPM! Same thing as you. I was told by my uncle (skilled, experienced mechanic) that he's almost positive that it's the synchros and the only thing that will fix it is going to be to either buy a new transmission or have mine rebuilt :( He said most likely the guy that had it before me didn't know how to shift and was the cause of the damage. Like you, he suggested changing the fluid multiple times, after the fourth time he told me that I was wasting money if I continued to do that and recommended the above.

I seriously appreciate you guys' help and guidance and look forward to any further suggestions/input.

The factory AZ6 has a rated capacity of 184 lb-ft per Aisin. A supercharger will be making around that at the rear wheels, so the starting point before headers/E85/higher boost pulley is ~15% beyond the factory spec. Cryo treating would improve strength and WPC would reduce friction, but there are more failure mechanisms than just the gears. The thrust load on 4th gear can chew up the adjacent reverse gear for example.

Okay understood. But from what is being said here and my very basic understanding (lol), I shouldn't even really be worried about the transmission failing under a typical supercharger setup? Or are you saying that the starting point added torque from a supercharger is going to be 15% above what the stock transmission is rated at and that I absolutely need to account for that? If so, how do I go about doing that? I'm very new to this, I'm just trying to cross all of my t's and dot my i's :iono:

Also it looks like the 4th gear thrust issue is resolved per this rebuild breakdown from Jack's:

https://www.jackstransmissions.com/i...product_id=483

1st - 6th Gear Synchros
Reverse Gear Synchro
3-4 Shift Fork
1-2 Gear Slider
3-4 Gear Slider
3-4 Gear Slider (Includes Over-Extension Modifications)
4th Gear Thrust Fix (Includes Custom Clips and Shaft Modifications)
5-Reverse Gear Slider
Input / Output Oil Seals

Dont worry. I bought a used 2013 with 58K miles and I am super charged with Flex Fuel. Really the main thing you need to worry about is the TOB if its original and slip on OEM clutch . Trans is good for much more power. not till you approach 325-350WTQ will you need to worry about certain gears in the trans

A little of both. You should be fine with a typical supercharger setup, but it's not completely risk free. I think most would agree that it's more practical to replace the trans if it breaks than to invest in an AZ6 build, and the Nissan 350Z's CD009 trans swap is cheaper and more reliable than the AZ6 build paths.

https://www.mazworx.com/mazworx-favq...t-frs/brz.aspx

I like this, if its a bolt in option, and not just parts I need to weld and bolt on to an existing gearbox.

Yeah TOB is original. Is there an upgraded option for that? Also I do plan on changing out clutch to something a bit better when I change the transmission. I've also been told that the clutch fork and pivot should be changed to ensure reliablity/durability.

Gotcha. I'm looking at ~$2800, for a performance rebuild of the AZ6 (that includes fixes for 4th gear thrust issues, CF synchros and WPC treatment). At that point I'd basically just have to bolt it back up to the vehicle. Is the CD009 trans swap just that easy? Because I don't think I'm ready for anything that is going to require welding and serious modification.

If you go this route I'd get the gears cryo treated too.

Why do you think cryo treatment is useless?