After discovering that my 2003 WRX 5MT broke a tooth on 3rd gear, I decided to rebuild the broken parts with Type RA gears. This post will cover the teardown and rebuild process.
Note: Because of the COVID nightmare going on, I didn’t get nearly as many photos as I would have liked. I didn’t have enough gloves on hand to keep my camera from being covered in gear oil. As a result, some photos are in various stages of teardown or reassembly.
I found the best way to work on the transmission is to stand it up on two blocks of wood to keep the input shaft off of the ground. I would also recommend taking a photo of your trans before taking it apart. Most of the little brackets have an obvious home, some others are less so.
The First thing is to remove the pin that holds the shifter linkage u-joint to the selector shaft with a hammer and punch. I am not certain if the shifter linkage bracket needs to be removed as well. I planned on cleaning my case so I removed it.
Whoever installed this wedged some shifter bushings from a different year into this joint. It was almost impossible for it to pivot and I needed to use a lot of force to pry them apart.
Next, I would go ahead and remove the wiring harness and any associated brackets.
While you still have the punch handy, I would hit both of the alignment pins on the tailshaft until they move. Mine was basically seized in place and would not release the tailshaft. I sacrificed a couple of plastic trim removal tools as wedges throughout this process as well.
Once the tailshaft housing is off, you can remove the transfer gear and output shaft along with the center differential, which is pretty heavy and covered in gear oil.
The center housing is more of the same, only the selector shaft comes out as well.
There is a spacer for 5th gear that is more or less just resting in place. That can be removed. Four bolts are holding the driven gears onto the case. These can be removed as well.
Now we need to lay the transmission down on its side; speedo sensor exposed. Then remove the remaining bolts that have corresponding nut on the opposite side of the case.
There are a couple of pins that are holding the cases together. One is below the speedo gear and the other is in the bellhousing.
Once the cases are split, the gears can be pull from the case.
At this point, I would clean up all of the mating surfaces, and clean out the case if you had a gear failure as well. If you have any seals you need to replace, this would be a good time to do that as well.
After the RA gears arrived, a friend picked them up to swap out 3rd and 4th gear. Unfortunately, I didn’t order the install kit at the same time so after I got the transmission reassembled, 3rd gear would pop out of gear with any load put on it. The hub/synchro design changed in 2004 and didn’t allow full engagement of the selector.
With the gears back in hand, the reassembly process can start.
The left side case.
We can drop in the front differential.
A quick note on the gear sets. There is a pin on the first bearing of each gear stack. Lining those bearings up with the pin in the case is an exercise in patience.
I’ve found it is easier to drop the driven gears in first, get that pin aligned, then throw a couple of those bolts in for the rear bearing to loosely hold the gears in place.
And then the input shaft or main gears can go in.
Before we can close this case up, we need to swap out the speedo gear. Rallispec recommends using a metal gear with a 3.9 final drive; 4.44 users can use the OEM plastic gear specific for the 4.44 FD. A snap ring holds the speedo gear in place.
I recommend a dry test fit of the case half before applying sealant. It should more or less fall right into place with only a couple of taps. I used Permatex Ultra Gray for sealant. The FSM calls for Threebond 1215B or equivalent. I ordered the Threebond from eBay and have yet to receive it. So far, the Ultra Gray has held up fine.
With the case halves back together we can stand up the trans and install the center diff housing along with the selector shaft. Before installing the center housing, check and make sure the transmission gears still rotate freely in neutral. If there is any binding, break the case halves apart and check to see if anything shifted. This happened to me on a couple of occasions.
With the center diff housing on, stick a screwdriver into the selector shaft and makes sure all of the gears work.
Then we can drop in the center differential and the transfer gear. The torque specs for the center housing is 18.1 ft lbs or good ole gutentight.
And finally, we can install the tail shaft housing.
I would recommend installing the shifter u-joint while the trans is out of the car. It is significantly less fun to install with the transmission in the car. And depending on if you are installing a new clutch or not (pull clutch), you may be able to go ahead and install the clutch fork and throwout bearing.
Glad I found this, just nuked my front differential after the tail shaft housing had a crack in it. Much more confident in attempting myself, I even have free access to a press.