Hey guys,

Just wondering how strong is the evo3 gearbox and transfer case compared to say a 99gc8 ?
Having to witness the failure of gc8 gear im curious as to how the mitsu gear holds up?

 

My Evo2/3 gearbox 4th gear started breaking when I passed 450+lbft tq. If you need more tq, you should setup boost vs gear and rpm to limit tq on 4th gear only.

 

what is 99gc8?

 

99gc8 is a V5 Subaru Impreza WRX, only the GC8 STi and STi RA came with better gearboxes for that generation, and they are still considered weak compared to the sti 6sp.

 

So if a non sti impreza drivetrain is compared to evo 3, how does it compare?

 

EVO is better. Use some good hear oil and an EVO3 will handle a lot of power. If you are making big power you can check for gear fatigue with Magnaflux and start with a good gear set. Subaru gears are junk. They break at stock power levels.

 

Also agree with above, the non STi GC era transmision is basicaly the same as the 200X - 2007 (before the hatch) wrx that can fail at a little over stock power, the RA gears (GC8 STi/RA) are considered next in line and some people have luck with them up to 330 - 350 whp, above that it´s either PPG gears or swap in a 6sp from a 2002 or above STi. As always it also depends on driver abuse.

 

Regarding the Evo 3 transmissions:

I agree, 4th gear failure can be an issue above 450 ft-lbs but there are things that can be done to reduce failures with power levels above 450 ft-lbs: running a thicker fluid such as a Redline 75w140ns, avoid doing 4th gear pulls when trans fluid is hot (Gear oil temp gauge or manual trans oil cooler), and lastly tightening the shaft preloads for the input, and intermediate shafts (and the center differential case preload as long as you're in there).

The center differential can also be a weak point on hard launches. Upgrading to a 4 spider differential or welding the differential will fix this.

I've built Evo 3 transmissions with the aforementioned modifications that have withstood 700+ ft-lbs of torque. They definitely won't last forever at that power level, however.