Why Can't Trudy Adjust Her Clutch?

Dear Car Talk

Dear Car Talk | Aug 06, 2012

Dear Tom and Ray:

What's the deal with nonadjustable clutches? I have driven manual transmissions my whole driving life. I own a 2007 Toyota Matrix, and when I started stalling it more often due to the clutch, I asked the dealer if he would adjust the clutch for me. He said, "No, the clutch isn't adjustable."

Of course, I'd never heard of such a thing, and wondered if he was just blowing me off as a "woman driver" who didn't know what she was talking about. Why would they make clutches nonadjustable?

-- Trudy

TOM: They don't make clutches "nonadjustable," Trudy. But they do make most of them "self-adjusting" these days, which means they can't be adjusted by your mechanic.

RAY: Since you've driven stick shifts all your life, you know that in the old days, clutches routinely had to be adjusted.

TOM: Normally, you always want there to be an inch or so of free play in the pedal. That means for the first inch or so that you depress it, nothing happens. The pedal just flops there. There's no resistance.

RAY: That tells you that the clutch is properly adjusted, and is not riding itself (being partially disengaged at all times while you drive around). Because a ridden clutch is a not-long-for-this-world clutch.

TOM: Normally, as a clutch goes out of adjustment, the engagement point (the point at which the car starts to move as you lift your foot off of the clutch pedal) gets higher and higher. Eventually, all the free play disappears, and then you're riding the clutch all the time without knowing it. It's as if your foot is partially on the clutch pedal, even though it's not.

RAY: Eventually, people got sick of having to (1) remember to get the clutch adjusted all the time and (2) replace their burned-out clutches when they didn't remember.

TOM: So, to satisfy their increasingly annoyed customers and protect their reputations for reliability, manufacturers started using hydraulic, or cable-based, self-adjusting clutches -- which do what? They adjust the amount of free play, all the time, by themselves.

RAY: At some point, when there's no more adjustment room left, then it's time for a new clutch. You may be at that point, Trudy.

TOM: If the engagement point for your clutch has gotten too high, that's probably the case.

RAY: But if it's too low, there are two possibilities. One is that some air may have gotten into your hydraulic system through a small leak in the slave or master cylinder. You can have the system bled to remove any air that's in there.

TOM: If it improves after being bled, your next step would be to find and fix the leak.

RAY: The other possibility is that you bought some extra-thick or all-weather floor mats that are making it impossible for the pedal to reach all the way to the floor.

TOM: My brother picked up another inch and a half of downward clutch travel by removing the full-pile shag carpet he had in his car.

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