'99 Forester, 180k miles, original clutch

 

My clutch recently went south, broke a spring out of the hub,

 

 

I'm happy with 180k of service out of the clutch, that's about what I've come to expect from my clutches as every vehicle I've owned that had a verifiable OEM clutch has gone between 170-200k.

 

But I've noticed that every clutch in every vehicle that I've owned since I started driving that I've needed to replace has never gone out because they were slipping, it's always because something breaks.

 

It's not the same thing breaking either, or at least not consecutively. I've had broken PP fingers, fried TO bearing, split shift fork, and worn out input shaft bearings.

 

Not all of the above examples are Subarus, but my question I suppose is towards driving style. I feel comfortable that my driving style doesn't burn out clutches which is why they never go because of slipping, but I wonder if I'm being too hard on them in some other way that is causing stuff to break prematurely.

 

I'm not one of those types that just HAS to achieve the given speed limit in the shortest amount of time possible, I feel I'm pretty easy on my cars in general.

 

But I thought I'd put it up to the board to see what ya'll think.

 

So what ya'll think??

 

Thanks!

 

Will-

From what I've seen broken springs are fairly typical on higher mileage clutches. Just metal fatigue I guess. When they have different sized springs the shorter (lengthwise) ones always seem to break first. Puts added stress on the other springs, they wear out. I've seen the longer springs with 1/8" between the spring and the hub at each end. With enough wear, and bouncing around between shifting and on/off throttle, I can easily see how one could fall out.

 

Excessive heating of the pressure plate causes the spring plate to lose tension. That combined with glazing of the flywheel and pressure plate surfaces (also caused by excessive heat) is usually what causes slipping. The glazed surface can be worn away with time, but it takes much longer because it is harder and smoother than the unglazed (un-heat-treated) metal.

Brakes work the same way. Glaze the rotors, and you can't stop anymore.

You get the most consistent wear from both the pads and rotors when they aren't heated to an excessive degree.

Keep the heat out and the clutch will last until the rivets wear into the flywheel.

 

What you have there is a well worn friction surface, and minimal glazing of the flywheel and pressure plate surfaces. Your flywheel wear is typical, just as a brake rotor wears with use.

 

That's about the best I can 'splain it.

That makes sense. I was also thinking,

 

I remember reading someplace that the flatness call-out for the flywheel is something like +/- .001" which is presumably so you have even contact along the entire friction surface. Any variation out of that range will force the disc to conform. Both my flywheel and PP were pretty badly dished. I didn't indicate them, but I'd guess by about 5 or 10 thou at least. I could see how the disc was having to flex quite a bit to do it's job and it just eventually couldn't take it anymore.

 

Will-

taking to long to let clutch out holds the car on the springs puts the whole wheight of car on those wimpy springs just hammers them out

Those wimpy springs take the full power of the engine all the time, it's a cush drive to help keep engine crankshaft vibrations out of the transmission. The crankshaft speeds up as each cylinder fires and slows down before the next one. The crank sensor is watching that speed variation and that's how it detects missfires. That constant surging would put more wear on the gears, so the springs in the clutch hub help even it out.

 

They, like anything else, wear out over time. There's two things that would hasten their demise; clutch dumps so they bottom out fully compressed, or lugging the engine so the power pulses are really working the springs back and forth.

Those wimpy springs take the full power of the engine all the time, it's a cush drive to help keep engine crankshaft vibrations out of the transmission. The crankshaft speeds up as each cylinder fires and slows down before the next one. The crank sensor is watching that speed variation and that's how it detects missfires. That constant surging would put more wear on the gears, so the springs in the clutch hub help even it out.

 

They, like anything else, wear out over time. There's two things that would hasten their demise; clutch dumps so they bottom out fully compressed, or lugging the engine so the power pulses are really working the springs back and forth.

 

 

 

Hmm, I think I see what you're saying. I don't do clutch dumps, not my thing, but I probably do lug the engine more than I should. I don't usually do it so deeply as to feel it in your bones or anything, but if I'm cruising to a stop on an uphill grade, I'll lug the engine a bit rather than downshift just to come to a stop in a short distance, things like that.

 

I dunno, I probably shouldn't over-think this. I'm getting good life out of my clutches so I suppose I should just shut up and be happy I'm not only getting 60k like my neighbor gets :cool: