Adapting a K20Z3 Transmission to Fit a 2002-2004 Acura RSX

Obtain a complete K20Z3 unit and set it on a clean bench where it can be stripped down. Every modification below happens with the gearbox out of the car and opened up, so treat this as a full rebuild rather than a quick external swap and gather your fasteners and small parts as you disassemble.

Split the case and locate the differential. Press the 2002-2004 RSX speedometer ring gear (part 41312-PPP-000) onto the diff. It seats with a light interference fit, so a shop press is not required; tapping gently and evenly around its edge with a flat punch and a hammer walks it into place. Keep it square as it slides on.

Pull the plug from the case fill hole, which is where the RSX vehicle speed sensor will live. Enlarge that opening gradually, dropping the VSS in repeatedly until it seats snugly with no play. Next, drill and tap a fastening hole beside it sized for a 10 mm bolt so the sensor can be clamped down. Flush every metal chip out of the housing when finished, since any shaving left behind will chew through the gearbox.

With the case open you have free access to wear items you would otherwise never reach. This is the moment to renew tired synchros, change gear ratios, or replace bearings. Reassembling first and discovering a worn part afterward means repeating the entire teardown, so address anything questionable now.

Before committing to sealant, perform a dry assembly. Put a marker dot on one tooth of the VSS pickup sprocket, set the sensor into its bored hole, and bolt the halves together with just a few fasteners so the case stays closed. Rotate the input shaft and watch the marked sprocket turn in step with the speedo drive. It must mesh cleanly and spin with the gear. If it slips or sits at an angle, the bore is probably oversized or the sensor is not pointing straight down; reposition until the pickup tracks correctly. Verifying this now avoids pulling the box back apart after it is installed in the car.

Once the pickup proves out, coat the sensor body with Hondabond, return it to its hole, and lock it with the 10 mm bolt. Then run sealant along the mating surfaces and torque the case halves together, reinstalling all the external hardware and small components you removed during teardown.

The Z3 shifter assembly will not carry over. Bolt on the RSX shift mechanism in its place. Two of its mounting points align with threaded holes already in the case; the remaining pair can be drilled and tapped for extra security, though the two factory holes combined with sealant are generally sufficient to hold it.

Swap the Z3 shift-cable bracket for the RSX version. Two of its three holes are already threaded and the third can be tapped or left as is. Keep the center fastener short, cutting the bolt down if necessary, so it does not bottom out deep in the case. Remember that a bottoming tap leaves the final few threads uncut right at its tip, so plan the depth accordingly. With the bracket mounted, the transmission is ready to install in the car.