>Initially everything works correctly. After about 5 minutes or so of driving,
>the car freewheels when letting off the gas when not in OD, or in first or
>second gears. The OD seems to engage correctly in third and fourth and not go
>in in first or second. When in OD, the car does not freewheel when getting off
>the gas. On the freeway, after 20 minutes of so of driving not in over drive,
>the car started to pop into & out of over drive (so I put into OD). The short
>term cure is to take it home with OD engaged and park it until I can get it
>fixed.
I have a '77 MGB with OD and while I'm not sure it's exactly the same as
your OD, I think their operation is similar. The OD is not meant to be
switched in when in first, second, third or reverse gears (on some models
I think it was engagable in third also.) There is a switch
mounted on top of the transmission that ensures this. An oil pump is
used to hydraulically engage a sort of clutch when switching the OD in
and out so if the oil level is low that might explain some odd behavior.
I've had a lot of trouble with the wiring on mine also. The wires
inside the gear shift lever get flexed a lot and can get pinched causing
them to break or short out. The wiring to the transmission switch is
open to the road so it deteriorates quickly. Also the switch itself
is susceptable to damage from water from the road. (Same thing is true
of the switch for the backup lights which is located nearby on the
transmission.) I seem to remember seeing a schematic which showed a
switch connected to some overdrives that is controlled by the vacuum
in the manifold. What purpose it would serve, I don't know (mine doesn't
have one), but it could be a source of the OD cutting in and out also.
And the solenoid in the OD that controls the oil flow (to engage the OD)
is somewhat notorious for failing partially, which can also cause
erratic behavior (mine is currently experiencing this. The OD works fine
usually at 55mph but as the transmission warms up or if I go faster it
-sometimes- starts to cut in and out. The wiring is ok and I opened up
the OD and the inside looks pristine so the solenoid seems the next most
likely suspect.) The oil pump inside might be suspect also but if it
was rebuilt recently it's unlikely.
Note that if you suspect your OD is not disengaging properly you
should not drive the car in reverse. There is a one-way clutch in it
that might be ground to pieces if you do.
When you discover the cause I'd be interested in hearing about it.
Ron
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