You mention replacing the clutch 500 miles ago. That sets
off lots of red flags in my mind. As I recall, you also just
rebuilt this gearbox (replacement O/D I think). Re-doing the
gearbox doesn't concern me overly much. I'd expect you to
have noticed if the various shaft bearings were bad (as in
floppy shaft).
But that clutch job... Bolts can, and do, work their way
lose. And folks can, and do, fail to properly torque things
some times (got a set of lug bolts to replace on a new
trailer axle because I forgot to properly torque them
myself).
Did you have the flywheel surfaced btw? As in, did you
bolt the flywheel back on? If so, you've got a chance of
having a flywheel fling itself off, if those are the bolts that
are lose. I don't recommend trying the experience of spinning
off a flywheel, especially with what Triumph used as a transmission t
unnel cover in the Spitfire.
If it were my car, and I'd isolated positively that it's engine
rpm related, not something like a bent pulley up front, and
I'd recently done clutch work, I'd pull the gearbox and make
darn sure I didn't have lose bolts holding the clutch assembly
or flywheel in place. When those let go, it can really be a
lousy experience.
And since I'd have the tranny out, I'd check the input shaft
by wiggling it and looking it over for fretting damage. I'd also
drain the gearbox oil to see how it looks (no sparklies), and
probably pull the top cover off to look at the various shiny bits
inside.
As to your questions, here's some answers. None are claimed
to be exclusive or exhaustive.
QUESTION:
- If the clutch pressure plate were lose...wouldn't I feel
it / hear it on actuation?
Answer:
Not necessarily. When you actuate the cluch (push in
the pedal) you press things together, greatly reducing the
ability for them to rattle around. For the clutch to disengage
the presure plate must be fastened to the flywheel. But
if the bolts holding it on were only slightly lose, you would
have enough hold on the pressure plate to allow it to
disengage when you push the pedal, but not enough to
hold it properly in place with the crankshaft spinning. The
flywheel could be lose on the crankshaft and the clutch
would actuate just fine.
Question:
- If the input shaft were damaged/broken...wouldn't I feel
it when letting the clutch out?
Answer:
Probably not. I've had two cars with bad input shaft
bearings that I never felt. One only let me know when it
ate the bearings (fascinating feel as they went through the
gear teeth). The other never let me know at all, until I
went to replace the clutch and discovered the input shaft
flopping (no bearing was left at all in that case). In both
cases, the input shaft was being held by the pilot bearing and
main shaft bearing adequately to perform. I doubt the Spitfire
gearbox is that accurate or strong though, so I would expect
some vibration.
Regardless, it's not something you'll feel through the
clutch pedal normally, it's something you'll more likely feel in
the shifter handle.
Question:
- If the bearings in the laygear were disintegrating....
wouldn't I feel it under load or sense it more on the transition
from power on to power off?
Answer:
Don't have experience on this, so my answer is purely
speculative. Since load puts a tremendous side load
against the lay gear assembly, I wouldn't expect it to
vibrate under these conditions. I'd expect it to vibrate
under very light load.
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