<VV> Unsolvable Clutch Problem in my FC

[Tom Suter]

I've apparently missed some off-list conversation about cable travel, but
have to jump back into this subject one last time.

The clutch pedal, cable and clutch mechanism were adequately engineered by
GM, and do not need to be modified to work right.  What most of us battle
while dealing with FC clutches 39-43 years later is that we still expect
old parts (particularly cables) to perform to original spec.  The major
variable that makes the FC clutch setup so frustratingly different from
cars -- both early and late -- is that the FC clutch cable is contained in
a sheath.  Car cables run over pulleys, so there is virtually no lost
motion between the clutch pedal and the clutch fork unless the cable is
near failure and actually stretching.  The sheathed FC cable, however, is
frequently accused of stretching when the problem is actually the fault of
the sheath.  When installed in the vehicle (even when properly attached "by
the book" to the pedal and clutch release clevis), the sheath of a worn-out
FC cable will compress and expand slightly over its entire length, eating
up enough travel to prevent full disengagement of the clutch.  Over the
years, there has been enough fatigue and outright loss of sheathing steel
to rust that the wire wrapping on the sheath it is no longer strong enough
to resist the compression and expansion forces.  The curves through which
the cable is routed under the vehicle have no bearing on lost cable motion,
since the cable is used for "pull" only, and is never pushed.

I challenge anyone fighting a clutch disengagement problem on an FC to
measure the difference between the cable input travel at the
clutch-pedal-end of the cable to the output travel at the other end of the
cable WHILE THE CABLE IS PROPERLY ATTACHED AND UNDER THE LOAD OF THE
CLUTCH.  You need at least 7/8" travel at the clutch clevis for the clutch
to disengage fully.  Anything less, and you have no chance of making the
thing work dependably -- if at all.  FCs that grew up on wet and salted
roads will predictably have much worse cables than those from rust-free
states.  Until recently, the only true solution has been to be lucky enough
to find a good used cable from a rust-free vehicle, but now The Source
(other vendors?) is offering NEW cables.  I've been out of the FC
"business" for a few years now, but this post and one a couple months ago
are based on my personal experiences and measurements.  I was fortunate to
find a great used non-Rust Belt cable, but would have gladly sprung for a
new cable if that had been an option then.

My thoughts -- your mileage may vary.

Tom Suter
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Hi Charles,

Well, if the cable is moving about 1 inch back at the clutch rod, then that
would rule out the cable itself.  If the pressure plate is in good
condition
with no broken parts then that pretty much rules that out. It could very
well be the pilot bushing.  Have you tried another one yet?  There are
several schools of thought on lubing the pilot bushing too.  Some say to
soak in oil or force oil into it.  I use a small dab of white lithium
grease
behind the pilot bushing and a very thin film to start out with on the end
of the input shaft.  Before I had done too many clutch jobs I used general
purpose grease and had problems with it gumming up and sticking.  It was
worse after it heated up and would do what you describe. You said the
clutch
disc itself is clean so that rules that out. Its not likely to be an
endplay
problem in the crankshaft because I had a crankshaft with over twice the
max
endplay and the clutch worked fine.

I would guess at this point that it is either the pilot bushing or the
cable
is just not moving enough back at the clutch rod.  The lengthening of the
clutch pedal should just about rule the cable but you could measure it
since
it is easier than pulling the engine again to get at the pilot bushing.
Sure sounds like something heating up though like the problem I had with
the
pilot bushing and lube.