Comparison of Subaru Gear Sets, WRX, Legacy GT, STI RA, and more...

I just had to rebuild the transmission in my 2003 WRX, and put in an STI V.6 Gear set. In the process of doing so, I decided to compare the gears going out, and going in, and I thought I would post what I found.

First, I actually had a set of gears from a 2006 WRX from an install that we did a while back. The first thing I did was to compare the 03 2nd and 3rd to the 06, and as far as I can tell, they are identical. I an 100% sure about 2nd, and 90% sure about 3rd. The reason for this is that 3rd gear went out on the 06, so there are no teeth on the driven gear. However, the tooth count is identical, and the base of both gears is the same.

In terms of 2nd gear specifically, we actually had both the 2002 and 2003+ second gear on hand. Here is a picture that shows the difference:

As you can see from this picture, the later generation 2nd gear was definitely thicker than the 2002 2nd gear, but the gear teeth count, and thickness is identical. You can also see that Subaru put two notches on the top of each gear.

Some people say that the early production '03s actually had the 02 gears, but I am not so sure... The part # for the 2002 2nd is 32251AA700, and it was used in production from Sept. 2000 through May of 2002. The part # for the 03+ started as 32251AA810, which superseded to 32251AA820 and was used in production from April 2002 through June of 2007.

Also, some other handy numbers to have are the serial #'s on the transmission bell housing:

The last 6 digits are as follows:

2002 - 4VN2AA
2003 - 4VN2BA
2004 - 4VV4AA

So from this, I can say that the gears in the WRX from 2003 - 2007 are for all intents and purposes the same. One interesting re-design I did notice is the ring on 3rd that keeps the hub from sliding into the actual gear itself. I noticed this because on my 03, it is a metal ring that is welded to the synchro, and on my 3rd gear, that ring came lose, and was basically chewed up (which accounted for some metal in my transmission). On the later WRX gears, and on both the Legacy GT gears, and STI gears that I put in, this has been done away with, and incorporated into the synchro design.

So on to the pictures. First is a picture of the WRX gears compared to the Legacy GT gears, and second is a comparison with the STI V.6 Gears:

It is somewhat apparent from the pictures, but more apparent in person that the Legacy GT and STI V. 6 gearsare thicker than the WRX gears.

But because it doesn't come through in the pictures as well as it could, I decided to take some measurements. Now, I will say that this proved to be much harder than I expected at first because of the shape of the gear teeth. I used a caliper, and tried as best as I could to measure at the base of the tooth above any curvature of the trough between the two teeth. But with that said, I am going to say that my measurements are accurate +/- 0.1mm, though I might be giving myself too much credit.

Here are the numbers that I got after measuring 3-4 teeth on each gear, and taking an average. It is also worth noting that the WRX gear have been run in a car, where the LGT and STI gears were brand new ,and the STI gears are also REM treated.

For the WRX Gears:

2nd - 5.35mm
3rd - 3.76mm

05 - 07 Legacy GT Gears:

2nd - 5.92mm
3rd - 4.41mm

STI V.6 Gears:

2nd - 5.92mm
3rd - 4.39mm

STI V.6 RA Gears:

2nd - 6.03mm
3rd - 5.28mm

So basically, I am going to assume that the Legacy GT gears and STI V.6 gears have the same tooth thickness which isn't surprising because they are the same ratios after all. And I'll say that the difference between 3rd gear teeth is just my measuring error.

Lastly, I have taken pictures of the RA gearscompared to the WRX gears. I have added the measurements above.

Also, for anyone interested, here are the ratios for the above sets:

JDM STI V.6