In a message dated 96-09-14 10:56:36 EDT, mood@rad.unc.edu (Jon Moody (BME))
writes:
>Is it possible(easy) to fit an A type Overdrive to a '73 TR6? What are
>the differences between an A type and J type and what are the pros and
>cons of each. Thanks.
>
>Jon Moody '73 TR6
Jon
It is easier to mount a Type A in a newer TR6 than to fit a Type J in an
older style (something I have done). The Type A will use the same mount as
the non-O/D transmission uses - which means the adapter bracket attached to
the later style mount.
The main differences between the type A and the type J O/D's are 1) the type
A has an accumulator which stores pressurized hydraulic oil (via a spring
loaded piston) and 2) the type J has a simpler solenoid.
The accumulator in the type A model stores pressurized oil (potential energy
stored in a spring) so that when the O/D solenoid is actuated the O/D shifts
almost instantly whereas the type J does not have an accumulator and when the
solenoid is actuated the O/D must wait for the pump to deliver enough oil to
shift the O/D actuator pistons. This may take as much as 3/4 (.75) seconds
at low speeds.
One side effect is that the type A O/D oil pump is always pumping against
pressure but the type J pump discharges directly to the oil sump when the O/D
is disengaged and hence uses no HP in this mode. (I've been told that the
O/D pump can consume as much as 5 HP at high speeds)
The other main difference is that the type A unit has a direct acting valve
and the type J model has a pilot operated valve. This means the type A
solenoid needs to be much stronger to overcome the pressure - especially when
actuating. This solenoid has two coils and a set of contacts. The pull-in
coil draws 10 amps and the contacts in the solenoid will de-activate this
coil once the solenoid is pulled in. The second coil holds the solenoid in
position and draws much less current.
The type J O/D has a pilot operated actuating valve which uses oil pressure
to operate the main part of the valve. Also since there is no accumulator
and hence no stored pressure at the time of actuation there is no pressure to
overcome and the solenoid required here is much more simple.
Pro's and Con's:
Well the type A actuates more quickly but both de-activate at the same rate.
The Solenoid on the type J is a single coil unit where the solenoid on the
type A has two coils and a set of contacts and the contacts can be a
problem.
The type A has an accumulator and the type J does not.
The type A easily mounts in early and late models. The type J does not
easily fit in the earlier models.
Internally they work the same and the gears and clutches may be
interchangeable although I have not tried it (It would be just like the Brits
to redesign something for no appearent reason). (A note to our friends from
the misty Isles: No offence)
I have used a type J O/D for 7 years and I am happy with it.
Well I think this answer is long enough for now.
Dave
TR6Massey@aol.com
St. Louis, MO USA
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