SPD Tuning Service
Page down for detailed information. Suggestions, comments and questions are always welcome.
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SPD Tuning Service Page down for detailed information. Suggestions, comments and questions are always welcome.
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Can I get a heavy duty clutch? There is some good news and some bad news. There are several HD clutch units for the WRX, but none of them will fit the 2.5RS. There will perhaps be a US after-market clutch in the future. How is a WRX clutch different from the 2.5RS? The problem is there are two different clutch designs. All normally aspirated Subaru engine use a typical, punched sheet metal, finger type spring clutch plate. A "diaphragm clutch". Pushing in on the fingers with the Take Out or Throw Out bearing to relax the spring holding the pressure plate against the flywheel disengages the clutch disk that was trapped in between. The T/O bearing is pushed forward toward the engine by a lever you can see sticking out of the top of the transmission, just behind the clutch hydraulic slave cylinder (or clutch cable for the non-2.5 engine folks). The part of the lever you can see is obviously pushed back toward the rear of the car so the bottom part can lever forward the T/O bearing into the spring fingers of the clutch pressure plate. This action relaxes the tension holding the clutch disk between the flywheel and the pressure plate. The clutch disk is attached to the input splines of the transmission and is held to the motor between the flywheel and the pressure plate so you can go down the road. Any Porsche mechanics in the house? There is more than the flat-4 design in common. The WRX clutch (all Subaru turbo clutches, Legacy or Impreza) is not a standard diaphragm clutch. It is a classic Porsche designed pull lever clutch. (Before you get too excited, it first appeared in the 1936 VW) This design uses a set of levers to lift the pressure plate off the clutch disk as opposed to the diaphragm clutch having its spring bent in. The long and short of it is that the T/O bearing lever moves in the opposite direction. It is pushed forward at the top of the transmission to pull back at the T/O bearing! Is this trivia or what? Subsequently, back at the ranch.... The left and right halves of the turbo transmission front case are different castings than the non-turbo transmission. The turbo lever arm operates on a large pin that is screwed into the case from the side. The non-turbo transmission uses a simple ball socket for a pivot of the T/O bearing lever. Because of the small (may we say non existent without offending the hopeful) demand for non-Turbo high performance Subaru engine and transmission parts, it is unlikely that we will ever see a true HD clutch for the non-turbo transmissions. I will be glad to be proven wrong at a later date. Although it is possible to convert to a turbo type clutch, you must re-shim the transmission bearings and the ring and pinion setup, as well as the check the transfer gear set shims, when swapping cases. This is not a shade tree operation. Close ratio, 4.44 final drive, turbo transmissions are $4300 new, same price as the non-turbo wide ratio box. The cost of the clutch bits are part of what makes the WRX cost more though. |
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