I am by no means an expert on overdrives. However, I thought the hydraulic
pressure required to engage the overdrive was created by a pump driven by the
main propshaft, and that at road speeds below about 30 mph there is
insufficient pressure to engage the overdrive. That is certainly the case with
the overdrive in my Triumph based home build Lotus Seven replica. So even if
for some reason the gearbox switch is still providing 12 volts to the
solenoid, at low road speeds there would be no possibility of being in
overdrive and reverse. My 100 has the throttle switched bypassed, but the
gearbox switch is in circuit. If I leave the dashboard switch on, and reduce
speed, it always drops out of overdrive sometime before I come to a halt.
Comments welcome!!
Mike Brooks
'56 BN2
Aboyne
Scotland
Message: 2
Date: Tue,
22 Jul 2008 15:14:42 EDT
From: Editorgary@aol.com
Subject: Re: [Healeys]
Overdrives
To: healeys@autox.team.net
Message-ID:
<c25.3eb0410b.35b78ba2@aol.com>
Content-Type: text/plain; charset="us-ascii"
>From philritten
You have all mentioned not to back up while in overdrive.
What if you
accidently flip the overdrive switch while idling in your garage?
As everyone has noted, with the system operating properly, there is a switch
near the base of the gearshift on the transmission that breaks the overdrive
circuit when the gear shift lever is moved oer into the first/second slot,
effectively preventing the overdrive from operating in either of those two
gears
or reverse (which is, of course, beyond the 1/2 slot).
HOWEVER,
Should
the overdrive be engaged with the vehicle moving forward, it is
possible to
get the car into reverse and start the car moving in reverse
before the
overdrive gears have had a chance to disengage. Then, if you immediately start
to move forward again at high speed, you can cause the overdrive gears to
break with a very loud boom.
If this set of circumstances seems unusual in the
extreme, ask me how I know
for sure that it can occur.
Moral of the story: Try
to remember to shift the car out of overdrive when
slowing down, such as when
you're coming off the highway by mistake on an exit
that goes directly into a
parking lot. Then try to remember not to rush your
shifts into and out of
reverse when you try to get back out of the parking lot
and on to the highway
to catch up to the rest of your group.
(the good news out of this story was
that I was able to replace my grenaded
1960 overdrive with a 1957 overdrive
which gives me a better cruising speed on
the highway.)
Cheers
Gary
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