View single post by Mark Rosenbaum
 Posted: 10-14-2005 06:55 pm
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Mark Rosenbaum



Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
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 Don't know how Holden did things.  The way I described is the simplest safe approach.  If you don't trust your switches to handle the current needed by the solenoid, then you can have the switches control a relay which in turn controls the solenoid.  You could also, perhaps, add a throttle position sensor such as the one used in the Austin Healey, to switch out of overdrive under full throttle conditions (much like the 'kickdown' in an automatic transmission).

The shift linkage cover has a boss for the overdrive switch and the linkage itself has the necessary protrusion to operate the switch.  As you surmised, the overdrive switch is automatically closed whenever the shift lever is moved to the 3rd or 4th gear position.

The shift linkage cover is supposed to be drilled and tapped for the overdrive switch, but this may have been neglected in some cases -- and if so, drilling and tapping an accurately located hole would solve the problem.  The overdrive switch and backup lights switch are identical.

There are several gear sets that can fit into the basic Sunbeam/JH transmission case, and these were listed in one of the other posts in the Engine & Transmissions category on this site.  The only way to know which set you have is to select first gear and count turns in versus turns out, or to take things apart and count gear teeth.