Some common problems people have when wanting to install a 6 speed into their 818 is finding a suitable unit that is supported by Factory Five’s FWD conversion kit. The fact that FFR only offers a conversion for model years 2006 & 2007 STI transmissions greatly reduces the number of available transmissions you have to choose from. Add to that the fact that those particular model year transmissions are highly valued by Subaru enthusiasts and you are left with high priced, often times abused, high mileage transmissions that are hard to find.

I will outline two ways to convert ANY 2001-2007 Subaru 6 speed transmission to FWD without needing the FFR conversion kit. I am not going to go over the many minor differences between each model year, or try to explain why one is better than the other. There are plenty of threads on other Subaru forums that expound on such things.

For the purposes of FWD conversion, we will group all 6 speeds into one of two categories based on the type of center differential they use. There is the Driver Center Controlled Differential (DCCD for short) and the non DCCD or viscous center differential (VCD for short). In US model vehicles, the DCCD units are found in the higher performance WRX STI cars and the VCD units are found in the Legacy Spec B cars. When looking at Japanese Domestic Market (JDM) vehicles, either can be found in all types of vehicles so its best to double check using the transmission code. The folks over at RalliSpec have compiled a chart of all the various model years and types of Subaru transmissions for your convenience.

For my 6 speed I chose a 2005 JDM 6 speed out of a Legacy Spec B.



The basic principle is very simple. Inside the 6MT there are two concentric shafts that spin independently of each other. The driven main shaft and the pinion shaft. The driven main shaft is hollow and the pinion shaft fits inside it. To force the transmission to only operate in a FWD configuration you need to lock the two shafts together so that they always spin in the same direction and at the same speed.





In either a DCCD or VCD type center differential there are always two splined parts that fit over each shaft to transfer torque between the driven main shaft and the pinion shaft. These are the parts that we will be focusing on. While this thread will be showing you how to convert a transmission that has a VCD, the concepts and techniques are the same for any type of center differential.

When converting to FWD you are trying to accomplish two things.

  1. Lock the driven main and pinion shafts together in a non permanent way. You need to be able to disassemble the transmission should it need to be serviced.
  2. Keep the locking mechanism in place when the transmission is rotating. You do not want your adapter sliding off when the transmission is spinning.


The next two posts will outline an easy methods and a more involved method to convert a 6 speed with a VCD type center differential to FWD.