Pressure Plate Finger Grooves, caused by the throwout bearing Options

[McMark]

Hey guys, check my logic here. I see this type of grooving all the time, on nearly every pressure plate I see - regardless of engine type, horsepower, etc. I hadn't given it too much thought other than, "I don't like it, but it happens every time." But I was just talking with someone and it occurred to me that this might be wear caused by a bad throwout bearing. If the grease is sticky, or if dirt has infiltrated the bearing, it may not be able to rotate/spin correctly and would slip causing wear.

The point of the throwout bearing should be to stop exactly this type of wear, right?
Doest this mean bad throwout bearings are super common?
Or is this a symptom of a loose clutch cable, not holding the throwout bearing tight to the fingers and that lets them slip?

[aircooledboy]

The point of the throwout bearing should be to stop exactly this type of wear, right?
Doest this mean bad throwout bearings are super common?
Or is this a symptom of a loose clutch cable, not holding the throwout bearing tight to the fingers and that lets them slip?

I always understood this was the opposite of a loose cable. I thought ideally your throw out should hover just out of contact with the pressure plate fingers to avoid premature wear to both the bearing and the pressure plate springs, but since many cars have their clutch cable too tight, you get this. (IMG:style_emoticons/default/confused24.gif)

[Dave_Darling]

I thought ideally your throw out should hover just out of contact with the pressure plate fingers ...

Not on a 914, at the very least! Remember, the 914 has a spring on the pedal cluster that pulls the pedal down in the "press the pedal" direction. That means there is always pressure on the throwout bearing--though not a lot.

This kind of wear is exceedingly common--maybe universal? I don't know why, because it seems to me that the T/O bearing should be there to prevent that. Especially if the bearing is always in contact with the fingers on the plate, so it should not have a chance to slip.

Maybe it would be worse without a real bearing in place?

Do you have photos of the throwout bearing?
What does the bearing surface look like?

The top of the bearing has a rounded surface. Basically it's just the inverse of the wear that you see in the pressure plate fingers in the pics above.

Here's a pic:
(IMG:http://www.914world.com/bbs2/uploads_offsite/www.pelicanparts.com-121-1418175958.1.jpg)


--DD

[DBCooper]

I thought ideally your throw out should hover just out of contact with the pressure plate fingers ...

Not on a 914, at the very least! Remember, the 914 has a spring on the pedal cluster that pulls the pedal down in the "press the pedal" direction. That means there is always pressure on the throwout bearing--though not a lot.

I don't think so. There's also a much larger spring on the transmission's clutch arm that pulls it back, disengaging. You need free play at the top of your clutch pedal, meaning no contact between the release bearing and the pressure plate until you press the pedal past the free play. I think those grooves are created from the friction of the "spin up" of the stationary release bearing as it matches speed after contacting the spinning pressure plate. When the grooves are deep that metal's gone and not coming back, so it's time for a new pressure plate.

When you sit at a stop light with the clutch disengaged you're wearing the throw out bearing, but much worse is that you're causing unneeded wear on the engine's thrust bearing. It's what limits the front-back movement of the crankshaft, and every time you press the clutch the pressure opens the pressure plate, but it also presses the flywheel and crankshaft forward, against the thrust bearing. And it's a heck of a lot more expensive to replace a main bearing set than a throw out bearing. You check how many miles are on the bug's T1 engine by pulling and pushing the crank pulley? Any movement is end-play from a worn thrust bearing, meaning a lot of miles on the engine (or a lot of time at stoplights with the clutch in) and an impending engine rebuild.