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I made an astonishing discovery......soft clutch on a hot day in traffic??? Read on..

1778 Views 4 Replies 4 Participants Last post by  Safir
Now I know why the WRX has the slave cylinder on the tranny instead of the engine block: Excessive heat.

In the past I have had problems with my clutch pedal "feel" becoming very soft and light in traffic on a hot day. It happened before with me when I had my old B-Spec clutch and Forester pressure plate. I now know what the problem is: heat.

Once last summer I was on the 91 freeway in stop-and-go traffic and my clutch became more and more soft. Eventually, the pedel stuck to the floor twice. Once I started moving, the clutch went back to normal.

Now I know why Subaru uses a pull clutch on the WRX!! The intercooler sits right on top of the clutch slave cylinder on my car. The slave cylinder becomes super heated and starts to lose its hydraulic properties. The pedel becomes spongy and in some cases fails completely when the fluid starts to boil.

Subaru must have also encountered the same problem with the intercooler mounted directly above the slave cylinder. Excess heat from the intercooler was superheating the clutch fluid.

The WRX uses a hydraulic system, but the slave cylinder is mounted backwards on the transmission instead of the engine block, away from the intercooler!

So in order to fix my problem, I have to either move the slave, find a way to cool the slave, or find a fluid with a very high boiling point. I think I will try a different fluid first.

The first time this happened, I thought is was the pressure plate or B-Spec clutch that was getting super hot. Now I know for sure that it is the location of the slave on factory non-turbo cars.

If you can think of a way to keep the slave cool during "spirited" driving, please let me know....
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Hey. You cross posting fruitcake!


See my other response.
ARG, the same thing happened to me just yesterday when I was sitting in traffic. I noticed that my clutch was quite a bit easier to push down, but didn't think much of it.

My situation wasn't as bad as yours since mine didn't stick to the floor. Interesting though how the location of the intercoolers and slave cylinders causes this.

My girlfriends car does that too, but it's not turbo... That does not make me feel any better about the condtion of the car...
Actually, the pull type clutch is used because it gives you a better mechanical advantage. That way you can use a pressure plate with more clamping force and maintain a softer pedal feel.

I would guess the heat thing is just a convenient side-effect
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