Hi folks
Been lurking a bit on the list
too busy to participate as much as
I'd like. But I've seen some clutch issues appear on the list lately
and I just thought I'd ramble on a bit about some clutch basics in
hopes of clearing up some possible confusion, even if it's just my
OWN confusion!
Two basic points that ought to be made:
1) With a clutch (and this goes for any car) there are really just
two failure modes: Failure to ENGAGE and failure to DISENGAGE.
2a) The clutch (disc and pressure plate) really only has one job: to
transmit power to the gearbox. If the clutch won't do that, then it
needs to be replaced.
2b) Conversely, it's the hydraulic and mechanical release linkage's
job to disengage that clutch to allow for shifting, starting from a
standstill, etc.
Failure to engage: I submit that there is a single diagnosis and cure
for the 'failure to engage' mode: replace the clutch disc and
pressure plate (and while you're at it, rear main seal, pilot
bushing, TO bearing, etc.) Note that there is no component anywhere
else, whether inside or outside the bellhousing which can cause this
type of failure.
Failure to disengage: This failure mode is a different story. Here
the situation is reversed in that neither the clutch disc nor the
clutch pressure plate are likely to cause this condition by
themselves. (there are exceptions
clutch disc sticking to the
flywheel and broken fingers on the pressure plate, neither of which I
consider to be very frequent or common) With this failure mode, it's
really just an actuation problem that has nothing whatever to do with
the actual clutch (disc and pressure plate, that is).
Unfortunately, this type of failure can be caused by several things
both inside AND outside the bellhousing. The mechanism develops a
lot of lost motion over time, the hydraulics (at least for me) tend
to be unreliable and that dreaded taper pin can shear off. And
that's just a few possible causes, and it's probably more typical
that the cause is a combination of all of these.
Judging from the traffic on the list (not to mention my own
experience) it seems far more common that the clutch won't DISENGAGE.
Generally, the only time you get a failure to ENGAGE the clutch is
after you've put some serious (hopefully) miles on it. An example of
this is when you're cruising along on an even throttle in top gear
and when you stomp suddenly on the throttle the engine revs higher
but you don't accelerate at all. That's a clutch failure, but it's
one that we all expect after x number of miles. It's no surprise
when a high-mileage clutch gives up and while changing a clutch is
never an easy job, it is a simple repair. I suppose that if and when
this happens right out of the box, it's the result of a faulty (weak)
pressure plate. And this failure to ENGAGE can be quite severe, too
I once had an acquaintance who owned a Nissan Pulsar that needed a
clutch. A buddy and I were pondering doing the work for this girl
(yes, it's always a girl, isn't it?) and had gone over to assess the
damage. In her case, the clutch was worn so badly that, with the car
sitting and the engine idling you were able to row through the gears
without touching anything but the gearstick. The clutch was
COMPLETELY disengaged, as it were, and as a result, the car wouldn't
go ANYWHERE under it's own power. Usually folks aren't so oblivious
as to let a bad clutch go that long.
Basically, I wanted to say this: If you can't DISENGAGE the clutch
on your TR, then the CLUTCH is doing it's job just fine. Don't look
at the clutch itself
it's not responsible. Look at the (many)
components whose job it is to disengage the clutch and you will find
the answer. Likewise, if the clutch is slipping (failure to engage)
then the clutch itself is NOT doing it's job and needs to be replaced.
Hope this helps SOMEBODY!
--
Pete Chadwell
1973 TR6
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