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Old 05-05-2021, 11:26 AM   #1
WrexKamdyn
Scooby Newbie
 
Member#: 524114
Join Date: May 2021
Location: Colorado
Vehicle:
2004 WRX
White

Default Swapping a manual transmission from a 2002 WRX into a 2004 WRX that is currently auto

Hello, I am new to Subaru's and am helping my son build his first car, a 2004 WRX. The car we picked up for him is currently an automatic but we also picked up a 2002 WRX as a parts donor car. One of the main reasons for this is because he wants to do the manual transmission swap. I have spent a lot of time reading forums and doing web searches to see if anyone has done this swap and it looks like many people have but there are only bits and pieces of information. I am hoping someone on here has done this exact swap, or knows how to do this exact swap. Based on the research I have found it appears these are the required parts needed from the 2002 WRX...

Manual Transmission
Clutch Set
Manual Transmission Mount & Cross Member
Rear Differential from same car (to make sure gear ratios are correct)
Shifter Assembly
Pedal Assembly
Slave Cylinder/Lines/Reservoir

I have also seen conflicting comments regarding the need for these items from the 2002 WRX...

ECU
Driveshaft
Front & Rear Axles
ABS Module
Gauge Cluster (so it does not have the automatic transmission indicators on it)

Finally, I have been trying to find info on the wiring portion of the swap and this is what I am finding to be most difficult. My automatic obviously has the TCU mounted to the pedal assembly with 3 plugs on it that will not be used for the manual swap. At the same time, my 2004 automatic does not have the 2 connectors that my 2002 manual has at the clutch pedal (blue plug with 2 wires & white plug with 2 wires). The 2002 manual also has a pair of what looks like relays screwed onto a metal bracket near the pedal assembly (2 white plugs, one of them has 2 wires and the other has 3 wires) that I am not seeing on my 2004. Does anyone out there offer some sort of plug and play harness for this type of swap? If not, does anyone know the correct way to wire these connections so that everything functions properly?

Any assistance would be GREATLY appreciated! Thank you for your time.

Ray
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Old 05-05-2021, 12:52 PM   #2
snow_bound26
Scooby Specialist
 
Member#: 395793
Join Date: Jul 2014
Chapter/Region: Tri-State
Location: SLC and Lake Placid
Vehicle:
2005 92x Aero
Beige

Default

Since you have a donor car right there, I'd recommend cutting out doing the wiring and just swap the bulkhead harness over.

Basically what I did, and am having no issues with, is the following:
On the manual car remove
-pedal assembly
-ECU
-trans
-CV axles
-driveshaft
-rear diff
-bulkhead harness
-slave cyl
-clutch master cyl
-ABS block
-trans subframe pieces
-center console parts specific to the manual
-shifter assembly

On the auto car remove all the same or corresponding parts. Install what you can as you go in the firewall. But the main piece to be done early is the bulkhead harness and ECU into the auto. Then just install in an order that makes sense.

This is a good time to replace all the shifter bushings, get the TiC shifter linkage, Group-N trans mount, rear diff bushings, rear subframe lock down bolts and Group-N engine mounts.

Feel free to PM with any questions. Did this on an 05 auto to 6 speed swap last summer.
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Old 05-05-2021, 11:55 PM   #3
AliBenn
Scooby Guru
 
Member#: 487
Join Date: Nov 1999
Chapter/Region: TXIC
Location: Houston TX
Vehicle:
1998 /2005 STunIcorn
Acadia Green USDM 22b

Default

Very good advice ^^^^^^
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Old 05-06-2021, 11:12 AM   #4
WrexKamdyn
Scooby Newbie
 
Member#: 524114
Join Date: May 2021
Location: Colorado
Vehicle:
2004 WRX
White

Default

snow_bound26, thank you for the response. I was considering doing the whole harness replacement as well but was afraid that since the harness is from a 2002 my son might lose out on some of the features that the 2002 didn't have. I was also not really wanting to take the entire dash out in order to replace the harness unless I absolutely have to. From what I can tell it looks like the main electrical things I would need to be worried about are the Neutral Safety Switch, Reverse Lights & Speedo/Cruise Control. Is there anything else that you know to be different in regards to wiring between the 2002 manual and the 2004 automatic? Thank you!
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