Worn out clutch

Worn out clutch: What happened?
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Introduction
The disc
The source of the problem
Disassembly

Introduction
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Normally, a worn clutch manifests itself as slippage. Simply put: you gas it, but the car revs more and goes less than what you've been used to. Feels like there's a sort of spin-up that's necessary before the car accelerates. My worn clutch was just shy of starting to slip, but had gone bad in another way.

Got a lotta miles on my car. Also have a manual transmission. In between the miles and me is...a clutch. We're on friendly terms, don't get me wrong, but there's a reason so many people have wandered over to automatic transmissions over the decades. About 90% of new car buyers, to be exact. Clutches are like first wives who haven't quite yet outworn their welcomes. They're fun, challenging, very satisfying, but a bit of a pain in one's sub-equatorial regions. I figure I won this marital spat: I made my clutch last 15 years and 255,800 miles.

For me the woes all started this past summer (2005), after the car had sat for almost three weeks when we were away. When we got back, the first thing I discovered was that the alternator's commutator and stator had corroded together, rendering the vehicle immobile. Never even got the car started. Off it went to the mechanic's. He replaced the alternator, but then discovered that the clutch was seized. It took a bit of jiggery-pokery to get the clutch to let go so the tranny could be placed in gear, but it eventually did. A short drive around, and it loosened up enough to feel OK after that. We weren't sure what the problem was, but since it had gone away we dismissed the issue, chalking it up to a friction disc stuck to the flywheel, which is common on older cars that are idle for a long time.

However, as the months went by, it became randomly difficult to get the lever into or out of gear. Usually the lever would go in easily, sometimes not. There appeared to be no real pattern to it. Since it was most evident on the 1-2 shift, I thought that synchro might be going bad, but there were occasional spells of easy shifting, where everything worked perfectly. The frequency of incidences of hard shifting were increasing, though, and then the 2-3 shift began to show problems. In addition, the clutch was getting very abrupt, and it required great care and gentleness to achieve a launch from standstill that did not chirp the tires. What on earth was going on?

Eventually I called my tech and told him what was happening. He agreed it was time to pull everything apart, especially considering the car's mileage and the fact that it was the original clutch. His first guess was that possibly a spring was getting ready to jump ship. What he eventually found was a bit of a surprise at first, but then made perfect sense considering everything else...

The disc
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This is the clutch friction disc that has endured 255,800 miles of Tegger's abuse.

Oh, by the way, you're looking at the pressure plate side, not the flywheel side.

This is the flywheel side of the friction disc.

The pressure plate side had worn out first. The flywheel side still had .020" of material above the rivets.

It doesn't look like it from this photo, but the disc measures precisely 8-5/8" across.

It may be hard to see here, but the rivets are staggered. Every second one goes through from the opposite face.

There are two friction surfaces. One faces the flywheel, the other the pressure plate (pressure plate side at top here). They are separated by wavy springs called a "marcel", and are secured to those springs by the rivets. The marcel's primary function is to help make clutch engagement more smooth.

The source of the problem
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Take a look inside the splined input shaft hole. See how orange it is? That's rust. It ought to be black with grease. That orangey dust was also on the input shaft. It's gritty of course.

Instead of the disc always kicking back a bit when the pressure pllate was pulled away, sometimes it did, but sometimes it bound up and remained in contact with the flywheel, which were the times when I could not change gear. Otherwise, the clutch was fine, except for lining wear. My tech estimates the clutch linings may have lasted another 5-10,000 miles or so if we hadn't had to fix the shifting problem the rust caused.

By the way, the white text says 1B.27. I don't know what it means. There are no other markings or text on the assembly.

Another silly side note: When you get the friction material wet, it really stinks. Sort of like fermented cow manure.

PRESSURE PLATE SIDE
The rivets are brass. It looks like the rivets had just begun to contact the pressure plate, as only some of the rivets had silvering on them from the pressure plate.

FLYWHEEL SIDE
There was about .020" of lining above the rivets. I had to wipe the dust off to mike them, and the brass was unscuffed.

Springs "popping out"
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Another type of clutch failure you may have heard of is "a spring popped out". What does that mean, and why is it bad for springs to do that?

When the clutch is used, those springs compress in order to help take up the shock of engagement. When they compress, they expand radially, and scrub against their housings. Eventually this scrubbing sandpapers the housing's lips away. For some reason, they seem to attempt escape towards the flywheel, so it's that side that wears first.

Below is an essentially unworn spring housing (from the pressure plate side). If you look very closely, you can see a tiny bit of wear in the extreme upper left corner of the spring, where it's dug in just a bit into its upper lip. Originally, all the housings looked much like this on both sides.	Another of the four housings, still on the pressure plate side. Check out the bottom right corner of the spring.There is a bit more wear on the lip from the first picture, and the spring's corner is partially exposed. You can see how the spring is clamped in place by the lips and cannot come out.

The flywheel side is very different, and suffers greatly from the stresses of spring compression and expansion. Note how the spring's coils have dug deep grooves into the housing's lip at the top of the photo. Note as well how the lip is totally gone at the upper left edge.	Another view of the photo to the left (rotated 180º). The harder one is on the clutch, and the jerkier one's starts, the more the springs compress in use and the more wear the lips suffer. If this lip had worn about twice what it has here, the spring would have eventually popped out and wedged itself between the friction disc and the flywheel, stranding the car.

Disassembly
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I'd like to take this thing apart to see how it works...

The rivets are quite soft, being brass. They drill out easily. Note that I need to remove only every other rivet. The ones left behind retain the flywheel-side friction surface. In other words, each friction surface is only held from one side. This is so the wavy springs (the marcel springs) will expand and push the friction surfaces apart.

The blue-steel "flower petals" are the marcel springs.

Direction of force is clockwise in this view. Notice how the marcel springs are extended in that direction, so they won't wind up when stressed. The marcel springs are very hard spring steel, but if you're particularly brutal to your clutch (dumping it at high revs, etc), you risk bending them. If they get bent, your clutch is wrecked.

Closeup of the marcel springs. They mike .035" in steel thickness, but "wave" out to about 1/16".

I've drilled off the other friction surface, as well as the large steel rivets that hold the carrier together. This allows me to disassemble the unit

The top part and the bottom one are riveted together as a carrier unit (the friction surfaces rivet to the carrier). The middle part is the splined hub that engages the input shaft. The splined hub is free to rotate inside the carrier, being limited only by coil spring pressure against the carrier.

You can see now more clearly how the coil springs are arranged in the unit.

See the beaver-chewed retaining lips on the flywheel side of the carrier?

Clockwise, from upper left:
Flywheel-side friction surface;
Flywheel side of friction surface carrier (and coil springs);
Various bushings and washers;
Pressure plate-side friction surface;
Splined hub;
Pressure plate side of friction surface carrier.