ViPeR_930

What would cause the clutch pedal to be harder to push in? I have an 05 with 70K miles that I bought 7 months ago and it's always been very stiff which I assume was normal. I hadn't test driven any other S2k. A buddy of mine just got an 05 and his clutch pedal is noticeably lighter. Is there something I can check or adjust? I've already lubed the clutch cylinder rod which made the pedal smooth (was already pretty smooth) but not any lighter. Any help or ideas would be much appreciated.

Soviet

Do you know if your pressure plate is OEM? The clutch pressure plate can dictate the stiffness of the clutch pedal. If you bought the car with 70k it is possible that it was replaced.

windhund116

Sounds like clutch disc maybe worn out.

darkevil3d

sounds like an aftermarket clutch with a heavy pressure plate

B serious

Could be an old pressure plate with springs that have hardened...or an aftermarket plate with heavy springs. Is the pedal travel smooth? Or is it choppy?

slalom44

Springs don't harden.

You likely have an aftermarket pressure plate. It's possible the splines on the tranny input shaft weren't greased adequately during the last clutch job but that usually causes it to grab or bind, not just get stiff.

B serious

Springs can be work hardened. I'm fairly sure that work hardening does not affect K factor in coil springs. Not sure if the leaf type springs in a pressure plate share that property or not. I was thinking that maybe a work hardened leaf spring may actually become stiffer?

I'm sure my thinking could be flawed. I'm not an expert on springs...and I don't do much work with spring steels.

Seems like older clutches are stiffer than brand new clutches of the same type. This could, ofcourse, be because of the grease becoming contaminated or less effective...or other factors.

I'm not the only one who has observed a significant pedal stiffness change with a clutch thats been used for a while. That's the reason behind my logic for assuming the springs are being work hardened. They are always pre-loaded, and they move quite a bit.

ViPeR_930

Thanks for the input guys. I guess I'll wait until the clutch needs replacing to find out for sure.

slalom44

Yes, your thinking is flawed. The OP is using the term "harden" to mean stiffer, or having a higher modulus of elasticity. You are implying that a heat treated steel strained below its elastic limit will see an increase in its modulus. That cannot happen.

Even if work hardening were to take place (I.e. working the material past its Yield Point and taking a permanent set) the modulus doesn't increase. Working steel could possibly increase its hardness, yield strength and Ultimate Tensile Strength but not its modulus.

The pressure plate is designed to withstand high cycle fatigue. That means it doesn't come close to the steel's elastic limit. This prevents fatigue failure over its useful life. So no - it doesn't work harden either.