On Tue, 5 Jul 1994, Dave Ahrendt wrote:
> I've just managed to get my MG-TC drive train back in the
> car after breaking the crankshaft on the way to the
> Burlington, VT. GOF last fall. All seems well, engine
> way up on power, generally smooth but for one problem.
>
> Just every now and then after shifting in fourth the car
> seems to have the shakes. The first time this happened I
> thought I had a flat. When this happens, if I just push
> in the clutch I have a 50-50 chance of the problem going
> away. If is doesn't just try it again and it will go
> away and the whole car just smooths out.
>
> I'm assuming that something went wrong in the clutch or
> my assembly of the clutch. Before I go pulling things
> apart is there a chance that this may be "normal" and will
> go away? I put about 800 miles since rebuild including
> a 500 mile round-trip to the Syracuse GOF.
That's definitely not normal, and I wouldn't count on it going away.
Trouble is, there are so many things that can give a TC the shakes, it's
sometimes hard to pin down, but I'll take a few stabs at it.
My first reaction was that you have a clutch problem, since disengaging
and reengaging the clutch usually makes the shakes go away. However, I
would expect that to show up in any gear (not just top) so it doesn't seem
too likely. I can't think of asnything you're likely to have done inside
the engine itself that would cause this. Let's look at external causes.
Does it really happen only when shifting into top gear? Is it more likely
to occur if you shift at low RPMs than at high RPMs? Did you install new
motor and gearbox mounts when you put the engine back in the car? The
mounts get mushy very quickly (especially the gearbox mounts), and when
they do, the engine/gearbox unit is not supported as rigidly as it should
be. When this happens, shaking as you described will occur when you start
off from a stop and when you shift at low engine speeds. Even with
good mounts, some shaking can occur if you habitually shift at very low
RPMs. TD/TF mounts are an entirely different design (including a torque
link), avoiding this problem.
Ummm, don't take offense, but you _did_ remember to bolt up the rear
mounts didn't you? :-)
In the worst case scenario, the rear mounts become so flexible that the
cast aluminum rear cover/mounting bracket takes more strain than it was
designed for and breaks. Then you'll have some _serious_ shakes!
Abingdon Spares used to sell a reinforced rear casting to solve that
problem, but I don't know if it is still available. Matter of fact, I
don't even know if AS is still in business. I've been out of the T-Type
parts loop for a while...
Maybe it isn't engine/clutch related at all. Does the shaking ever occur
when you're just driving down the road in top gear (i.e. when you're not
shifting)? Are the shakes transmitted back through the steering wheel?
Does accelerating hasrd make the shakes go away? Does the car tend to
wander rather than tracvk easily in a straight line? If yes to all of the
above, then suspect front end and/or steering problems. The TC's front
suspension and steering wear pretty rapidly, and can cause pretty bad
shimmy problems, including during power off/power on transitions as when
shifting gears. It's more likely to happen at higher road speeds, which
could explain why you notice it only when shifting into top gear. If your
TC has those 3 degree shims between the axle and spring mounts, take them
out. These were introduced part way through TC production to reduce
steering effort (as a sop to the U.S. market). Trouble is, they reduce
caster too much, which can lead to front end shakes at high speeds if the
rest of the suspension and steering isn't in absolutely perfect shape.
If anything else occurs to me, I'll write again.
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
feold@umd5.umd.edu 1962 Triumph TR4 CT3154LO (daily transportation)
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