[Healeys] Overdrive wiring question

BJ8Healeys sbyers at ec.rr.com
Mon Sep 4 16:15:54 MDT 2017

The manual says:

"Connect a low-consumption test lamp (a 12 volt 2.2 watt fascia panel light bulb is suitable) [I made a test lamp out of a single filament turn signal bulb and a spare bulb holder I had lying around] between the top terminal "A" (Fig. G.13)[of the throttle switch] and a convenient earthing point.

  The bulb should light when the overdrive and the ignition are both switched on, and the gear lever is set in the third or top gear position.

  When the overdrive is switched off, the bulb should remain alight with the throttle still closed.

  Progressively open the throttle by means of the accelerator pedal until the light goes out.  Check the position of the throttle opening when this occurs:  it should be one-fifth open.  This position of the throttle has been reached when a 3/16 in. (5 mm.) diameter rod can be just passed between the throttle stop screw and the stop lever on the HD type of carburetter, or when a feeler gauge of 0.048 in. (1.22 mm.) thickness can be inserted between the throttle stop screw and the stop on the H4 type of carburetter used on earlier engines."


The manual procedure would account for any system slack, but it also requires two people:  one to operate the pedal and another to monitor the light and check the position of the throttle plates when it goes out.  It would also require access to the throttle plates, and an estimate of what is "one fifth open".  If that is related to the 3/16" rod, then why not just use the rod and adjust until the light goes out?   

I have an "overdrive warning" light just above the dash switch that I installed back in the '80s when I didn't mind drilling a new hole in the dash.  When the switch is adjusted properly, the light stays on when the dash switch is turned off and then goes off with what seems to me a reasonable movement of the pedal.  I would say it isn't necessary to account for slack in the system when using the 3/16" rod.



Steve Byers


BJ8 Registry

AHCA Delegate at Large

Havelock, NC  



From: Healeys [mailto:healeys-bounces at autox.team.net] On Behalf Of Bob Spidell
Sent: Monday, September 04, 2017 1:14 PM
To: healeys at autox.team.net
Subject: Re: [Healeys] Overdrive wiring question


I'm working from memory--will check the manual later--but the way I interpreted the instructions were to adjust the switch with the throttles a spec distance--prob. the 3/16" as Steve mentions--opened.  For some reason, I thought this should be achieved by pressing on the accelerator pedal to achieve this setting which, of course, would pull up any slack in the Rube Goldberg throttle mechanism.  So, I set it this way but felt that it required too much pedal when disengaging the OD.  I just fiddled with the adjustment to where the OD disengaged with what I felt was appropriate pedal.  Maybe the 3/16" should be measured without allowing for linkage slack, maybe not; does anyone know for sure?



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