I replied to the previous portion privately, but I wanted to address
some of this as well on the list at large:
~ >Date: Mon, 9 May 94 13:36:53 EDT
~ >From: bobj@meaddata.com (Robert Jones)
~ >Subject: Broken Clutch?
~
~ >today I was leaving a parking lot when I pushed the clutch in to
~ >sshift gears I got an awful grinding noise (I felt it through the
~ >pedal too). The car runs fine in neutral, but when I push the clutch
~ >in, it grinds like mad.
A subtlety: You're in neutral. No grind. You press on clutch.
What happens? Does it grind immediately, or does it wait till
you try to select a gear first?
~ >I assume this means I had a catsrophic
~ >failure of some part of the clutch. Do these symptoms strike a cord
~ >with anyone? I have had what I would call clutch related problems
~ >lately, it hasn't wanted to engage fully, sometimes making it hard to
~ >get out of gear.
~
~ No question about it, bad pilot bearing. Thats the bearing that goes
~ between the input shaft and the flywheel. It spins when the
~ transmission is in gear and the clutch is depressed. When the tranny
~ is in neutral, the input shaft spins freely as it isn't connected to
~ the output shaft.
I've never had a pilot bearing go bad. I *think* I see what you
mean, though let's leave the output shaft out of it, as that just
confuses things. It's the INPUT shaft of the transmission that
runs against the pilot bushing; and yes, if you're in neutral,
the input shaft and the pilot bushing could be welded together
as they spin at the same rate. But when you press on the clutch,
the friction disc disconnects from the flywheel, and there could
be friction between the input shaft of the tranny and the pilot
bushing. If the noise starts immediately upon pressing the
clutch, the pilot bushing could be suspect.
On the other hand, Bob gives the classic description of throwout
bearing failure. That's the bushing that presses the release
bearing on the clutch cover (or pressure plate); when you push
this far enough forward, it releases pressure on the clutch disc
(or friction disc). It therefore follows that if you can't make
the release bearing go FAR enough forward, the clutch won't
release, providing exactly the symptoms Bob described. I *have*
had this experience. There are at least two common failure
modes, general wear and catastrophic failure. General wear is
gradual, and as Phil Ethier said is designed into the system as
a way of compensating for the wear of the clutch plates; as the
clutch disc gets thinner, the T-O bearing gets thinner too and
it all works out. Catastrophic failure hit me once, in which
the carbon ring that covers the T-O bearing's friction surface
actually delaminated from the bearing, and the clutch ground
and graunched on every shift just as though it had no fluid.
(Note that a badly collapsed T-O bearing will cause grinding
immediately on pressing the clutch, while a worn-out one usually
is silent till you try to move the gear lever. That's why I
ask that question up above there.)
Two other things can cause the same symptoms: low/missing clutch
fluid and a hole in the clutch line. However, these two failures
typically have another symptom -- flapping clutch pedal. If your
clutch still *feels* about right, it's probably the throwout bearing
(sometimes called the throw-UP bearing).
The bad news is that the T-O bearing requires separating the
engine from the transmission to replace it. Rent a hoist,
get three friends, and do it in a weekend, but it's miserable
work.
Now if you're *very* brave, and clap your hands extra hard to
show Tink that you believe in fairies, you can drive home without
depressing the clutch. First, you have to start in gear, so shut
the car off and select a gear that points you in the direction
you want to go. Be ready to shut the motor off if you get too
close to something, like your boss' car or a truckload of
nitroglycerine or something equally dangerous.
So let's assume you're pointed toward the open road with no
intervening traffic. With the motor off, you select first
gear (assuming that the motor has been warmed up so that it
will catch easily, of course), then turn the key. With luck
your engine will varoom to life after the vehicle shudders a
few feet ahead. Once the motor catches, drive normally, at
least till you have to shift.
When that happens, let up on the gas and you should be able to
slip the gear lever out of gear relatively easily. Then it's
a simple matter of matching RPM. This, of course, is much like
saying that the Chopin A Flat Polonaise is simply a matter of
pressing the keys in the right sequence. The object is to rev
the engine to about the speed it would be traveling if it were
already in the next gear; if you match them -- and I've had to
do this a number of times in several different cars, so it can
be done -- the gear lever slips in like magic. If you don't
match them, it can take some grinding, some graunching, and
some whirring. Don't force anything -- remember, vary the
engine speed while keeping up constant pressure.
The first time this happened to me (in my '84 GTI, the Biscuit
Tin of Steel), I was in rush-hour traffic at the top of Sepulveda
Pass on my way home from work. I hated that car by then already,
so I decided to tough it out. I managed to get home without
having to shut off and restart more than about three times, not
a mean feat in L.A. rush hour freeway traffic. The clutch cable
would snap on that car from time to time; the next time it went,
I managed to get around for three days before I had the cable
replaced. I've also had to do this once in the Volvo, when the
plunger that goes from the pedal to the cylinder popped out of
its circlip (Kim had parked the car when this happened, not
knowing what had busted; I ended up driving the car home where
I saw it was just a circlip.)
~ To replace, you need to remove tranny and clutch. Pilot bearing can
~ usually be removed with a slide hammer. I almost always replace the
~ clutch plate at the same time as I realy don't want to remove the
~ tranny again in a month or so.
In addition to that good advice, I'll add the advice to replace clutch
plate and throwout bearing in pairs, unless you KNOW that the one you
are leaving in the car is less than a few thousand miles old. The
throwout bearing costs less than $20, and the friction disc (um) about
$30 or so if I recall (MGB prices), and this is a minuscule portion of
the amount of work that goes into the replacement.
--Scott
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