Date: Tue, 21 Apr 92 11:28:15 EDT
From: Jim Muller <muller@alliant.com>
Someone else pointed out the danger of using OD in too low a gear. Perhaps
one should avoid using the OD in 1st or 2nd even if it can be engaged.
On the other hand, it certainly is easier to wire up a relay off the
backup light than to fabricate a bunch of lost parts. At least you get
some protection against one of the several ways you might abuse it.
Indeed. I don't fully understand the J-type, but running an A-type O/D
in reverse will destroy it instantly. Running with too much torque
will just cause it to slip, which isn't instantly fatal and you might
even notice if you are looking for it.
I don't know that shifting abruptly is a problem. The various manuals and
such say to shift the OD while under full power, and when it shifts, the
result is, shall we say, instantaneous. But that seems to be the prescribed
mode of operation, not that the various B-L manuals ever were that accurate.
Actually, the Laycock overdrive is perhaps the pinnacle of man's
achievement in the field of automotive engineering, or at least cool
gadgetry. In particular, it is specifically designed to shift at full
power. The actual rate of engagement is controlled by restrictors in
the hydraulic system, which causes things to happen at just the right
speed.
Just curious, though, wasn't the later Spitfire OD the J-unit (or whatever
the letter was) the same as used on the later TR-6's? If so, it is very
unlikely that the Spitfire motor can over-torque it, even in 2nd (and 1st
would be kinda' silly).
The type letter is a general design designator. Within the class,
different applications used different size actuating pistons,
hydraulic restrictors, and so on. I suspect you're right, but I
wouldn't assume that TR6 and Spit units were the same (again, I don't
know much about the J-type or its applications specifically, though).
-john
jtw@lcs.mit.edu
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