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Old 11-13-2003, 12:47 PM   #4
Homicidal Maniac
Member#: 1612
Join Date: Jun 2000
Location: Austin, TX
2008 STI

Default Transmission Specifics:

Q: "Can I use <insert engine here> with <insert transmission here>?"
A: The answer is almost a resounding yes. All EJ series engines share the same bolt pattern on the bellhousing. While some use fewer bolts than others, they will still bolt up.

One caution: the turbo transmissions use a pull-style clutch whereas the NA transmissions use a push-style clutch. If you are swapping transmission types, you need to match the transmission up with the correct clutch/flywheel assembly.

One more precaution: if you are swapping in a transmission, you need to be sure that your rear differential final drive ratio matches the final drive ratio of your transmissions. Installing a new transmission without checking this could permanently damage your center differential! Putting an engine from a FWD car into an AWD car or vice versa does not change the swap criteria as it will still all bolt together.

Thirdly, the older transmissions use a different shift linkage joint attaching to the shift forks of the transmission. The older transmissions have a fork that attaches to the rest of the shift linkage whereas the newer transmissions have a barrel joint. This must be updated if you are to change from an older tranny to a newer one or vice versa. It is believed that the older style shift linkage was used up until 1997. Beyond 1996, the transmission linkage should be the new style.

Finally, the older transmissions utilize a stud on the transmission for mounting the lower hole of the flange of the starter. If you swap in a newer transmission onto an older block, the block will not have the threads for the lower starter bolt. Some have reported success with just using the upper starter bolt, others have tapped a hole into the block.

Q: "Why can't I just swap in a new engine and leave everything else?"
A: Good news, you can! The structure and strength of the transmission is realtively unchanged since the 1993 Imprezas (not necessarily a good thing). There are some exceptions though: the turbo Legacies had a more uniform metal composition in the gears while the new STi comes with a robust 6-speed. Other than that, the gear strength is almost the same. You can read all about this here:

Q: "I have a FWD Subaru, can I convert it to AWD?"
A: As previously stated, Subarus are very interchangeable. If your car came with an EJ series engine, then any other engine components from an EJ series engine will drop into your chassis. Most of the time, you can't slowly convert to AWD; many of the components require the removal and/or installation of other components to work.

Q: "What components are needed to convert a FWD Subaru to AWD? Also read as 'Transmission swap technicalities'"
A: A new transmission will be required. Along with the new transmission comes the front diff, center diff, and tailshaft. You must also get the corresponding driveline for the transmission (side note here, if you are merely swapping one AWD transmission for another the MT typically shares one driveline between all other MTs and the ATs share another driveline; the STi 6-speed uses an AT driveline). There are many rear diff options, and any of them can be used as long as the final drive matches the final drive of the rear diff of the donor car the transmission came from. Front axles should be interchangeable, but newer axles are thicker. CV strength has remained the same and are not a weak point. Rear open diffs can be found on most Subaru models. Rear LSD s came on some Legacy Turbos, Some SVXs, 2000-2001 2.5RSs, and 2002+ WRXs. While final drive ratios vary, the axle splines do not. Your diff choice governs which rear axles are to be used. You will either need rear axles from an open diff Legacy or GC/GF/GM Impreza for an open diff or rear LSD axles from a 2000-2001 Impreza 2.5RS (ask for axles from 05/2000+ to be safe) for a rear LSD. If you are converting from AT to MT or viceversa, you will need the corresponding ECU since the AT ECU expects a TCU signal. You can spoof it as some have done.

"What else is needed?" Along with the basic driveline components, you are going to need most of the rear suspension and mounts from the transmission back. This includes the transmission crossmember, rear diff crossmember (and all in between), AWD gastank with driveline hump, struts and springs, AWD knuckles, a plethora of bushings, with the possibility of lateral links, swaybar, and trailing arms also being needed. Your best bet is to find an entire donor car that can be stripped. If that is not an option, you will be, as beachbum has said, 'nickle-and-dimed to death'.

Q: "Which cars have rear LSDs and what are their final drive ratios?"
A: Use the following link to find the details:

Q: "What axles do I need to use with my transmission and rear diff?"
You can read about axle compatability here:

Q: "I'm swapping transmissions. What clutch and flywheel do I need to use?"
The clutch and flywheel needed for your transmission swap are dictated by the transmission itself. If you are using a turbo transmission (commonly found in turbo Subarus like WRXs [non 6MT] and Legacy turbos) then you will need to use a pull-style clutch and corresponding flywheel. If you are using a transmission commonly found on a naturally aspirated Subaru, you will need to use a push-style clutch and flywheel.

Q: "I'd like to convert my clutch system from cable operated to hydraulic, what do I need to do?"
Here is a thread detailing a conversion from a 1996 cable operated transmission to a 2003 hydraulic transmission:
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Last edited by stimpy; 09-24-2004 at 09:09 PM.
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