In a message dated 96-03-19 03:47:10 EST, bc433@scn.org (Bob McLaughlin)
writes:
>Fellow SOL's, I need some advice. My 71 TR6 overdrive has
>developed a relay buzzing or chattering sound. Sometimes when
>it has completly warmed up, the chattering stops. The noise
>doesn't seem to affect the operation, but I can't bring myself
>to operate it making that kind of noise. The non-overdrive op-
>eration is fine as well. If anyone has had similar experiences,
>I'd like to hear your soloution. Thanks in advance.
>
>Bob McLaughlin
>'71 TR-6
>
>
Dear Bob:
The 71 TR6 used the type A overdrive which is the same unit used on TR2-5
(250) and the early TR6's. It is also the unit used on Austin Healays and
Jag's. This OD uses a solenoid which contains two coils. One coil is used
to pull in coil and holding coil. The pull in coil draws much more current
and has a lot more force necessary to pull the solenoid into the energized
position. However the heat generated by this coil would burn it up.
Therefore there is a set of contacts which de-energize this coil when it
reaches the pulled in position. To maintain the coil in the energized
position is another coil called the holding coil. If the holding coil was
not working the symptom would be what you described. The pull in coil would
pull the solenoid in until the contacts de-energized when the solenoid would
drop out but when it drops out the contacts make again and the cycle repeats
itself. This is called a relaxation oscillator.
When you say it eventially straightens out could indicate that the holding
coil connection is intermittent. All these connections are internal to the
solenoid and is not self evident. You were right to not continue to operate
this way. This action will soon burn up the internal contacts in the
solenoid. Check the adjustment. The problem may be something as simple as
being out of adjustment.
Good luck and let us know what you find.
Dave
TR6Massey@aol.com
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