Throttle position switch problem

[jedwards]

Gentleman,
I am having trouble setting my throttle position switch correctly and wondering what I am doing wrong.  I understand that it should be  closed until around 1000 rpm  then should go open circuit as the butterfly shaft rotates off idle.   I understand that the switch on/off point is adjusted by rotating it switch within the english long holes and against its internal spring to achieve this open/closed transition point.  However mine will not rotate far enough anti-clockwise to reliably CLOSE at idle. I can only assume that I must installing it  wrongly to start with.

Firstly, I bench test the switch. Seems perfect.
When installing the switch, I assume the body of the switch should be on the firewall side of the shaft as in the pictures I find on the web.   At idle, the flats of the butterfly shaft face basically up and down. From that I assume  I need to mate the switch’s female receptor with the flats on the shaft and then rotate the switch body anti-clockwise about 45 degrees to pre-tension the spring.  If I do that, I run out of adjustment and the switch is right on the trigger point with no throttle at all and no more adjustment left.  I have even milled out the holes on the switch body a bit to try to get more adjustment.

Any help would greatly appreciated.

[ctaylor738]

I have a spare switch that seems to work.  I clamped it in the vise the way it would be installed and put my meter on it.  The switch closes when the straight/flat edges that fit over the throttle plates shaft are horizontal. Don't see how your setup can work if your shaft is vertical with the throttle plate closed.  Wish I could help more.

CT

[jedwards]

You are quite right Chuck, my mistake. With the throttle closed, the throttle shaft's flats are horizontal.
Throttle is binding slightly, so I know that part is correct and at idle is fully closed. But I still I have very limited adjustment and the throttle position switch is closed (on)  only while the throttle is hard on its stop and binding slightly. Even the tiniest movement makes the switch go open.
I have re-soldered the internal contacts  in an attempt to build them up to make a bit of  room and have leaned the fixed contact as far forward as I can while maintaining a flat contact surface.
But in spite of all of this, and with the switch body fully rotated a get no useable adjustment at all.
Has anyone else experienced this?

[ctaylor738]

Well, the sticking and binding business is very subjective.  Why not try backing off the stop screw a bit to get the contacts in the switch to close consistently?  Don't forget to adjust the linkage to compensate.  BTW, are you sure that the linkage isn't pulling the lever off the stop I.e. a little too short on the rod?

[jedwards]

Hi Chuck,
I've been doing all my adjustments with the throttle rod disconnected and have adjusted the stop so it is not interfering with any of there adjustments. I've even removed the throttle lever completely just to ensure that nothing is altering the throttle's natural stop position. All that seems to be exactly as designed, which leaves me wondering if the internal contacts of my switch may not be right.
I have built mine up a little with fresh solder but maybe  they should have a points style  solid contact.  I just don't know.
Does anyone have a spare that they could photograph the internal contacts for me?

[ja17]

Good used switches should be easy to find. They used them on sedans of the era also. Even the carbureted finbacks and early W108s with automatics used the same switch on the front carburetor, I believe. If you need more specifics let me know.