Sounds like Brian has the right story!
I hereby retract all my objections to slowing O/D engagement by adjusting the
operating
lever.
However, since I've personally seen two different units that were marginal in
2nd gear
behind somewhat tweaked 4 bangers, I still plan to declutch ... <g>
Randall
"Power British Performance Parts, Inc." wrote:
> Randall Young wrote:
>
> > Tony :
> >
> > The problem is that, to engage the overdrive, the lever does not open a
> > valve, but rather closes it. The valve is actually a bypass that bleeds
> > pressure out of the O/D hydraulic system when the O/D is disengaged. If
> > the valve does not close fully, then your O/D is operating on less than
> > normal pressure, which can lead to slippage under load, especially when the
> > oil is hot. Of course, slippage heats the oil, which increases the
> > slippage ...
> >
> > Not a good idea, IMO.
> >
> > If you really want to reduce the operating pressure, there is an adjustment
> > (at least on the early A-types) to do so. It is not dependent (much) on
> > oil viscosity and so is temperature independent.
> >
> > Everything I've read on automatic transmissions (which bear at least some
> > resemblance to our O/D boxes <g>) suggests that fast clutch engagement
> > reduces wear. (as long as the other components can stand the strain <g>)
> >
> > Randall
> >
>
> Randall, not a flame, but I beg to differ on the function of the lever.
>
> Quoting from the "Service Instruction Manual for the Laycock-de-Normanville
>Overdrive
> Unit with Electric Control" publication no. 502274, it states:
>
> "The operating valve chamber is an enlargement at the top of a vertical hole
>in the
> overdrive casing. It is sealed with a screwed plug and contains a spring and
>plunger,
> which hold a steel ball downwards against a seating, to prevent oil from
>circulating
> to the operating cylinders. The valve is a hollow spindle sliding in the
>hole with a
> conical seating for the steel ball in the top end. When the valve is lifted
>by the
> cam lever it seats against the ball which is then lifted, admitting oil from
>the
> pressure accumulator via the drilled passage to the passage and into the
>operating
> cylinders, moving the pistons forward to engage the cone clutch.
>
> When the valve is lowered, the ball is allowed to come onto its seating in
>the casing,
> cutting off the supply of oil from the accumulator.
>
> Further lowering of the valve brings it out of contact with the steel ball,
>allowing
> the oil from the operating cylinders to return along the passage and down
>inside of
> the valve, to discharge through the small restrictor jet into the sump of the
> overdrive body. The jet is of such a size that the cone clutch takes about
>half a
> second to move back under the influence of the clutch springs."
>
> The above publication applies to A-type units only.
>
> Using the same logic that the restrictor jet smoothes out the disengagement,
>I also
> have my valve set to just crack open a few thou by setting it with a dial
>indicator
> directly on the ball. My OD never slips even lugging under heavy loads in
>the lower
> gears, and the engagement and disengagement is so smooth that if you didn't
>hear the
> change in engine RPM, you wouldn't know it even did anything.
>
> I believe the reason for setting the lever as suggested with the alignment
>hole is to
> facilitate quicker assembly, and a more "idiot-proof" repair at the
>dealership level.
> On the later J-type units, this adjustment was elminated and the function of
>the
> hydraulic circuits is drastically revised more in line with what you initially
> described as the "bleed-through" circuit. The engagement was also
>significantly
> smoother on the J's than on the A's
>
> Again, not a flame, just presenting information from a rare factory
>publication which
> others may not have access to.
>
> Brian Schlorff '61 TR-4 '64 TR-4 '72 TR-6 '79 Spit
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