All,

Whilst trying to get my idle speed adjusted downwards (currently about 1000 rpm at N.O.T.), I discovered this limit switch, which is integral to the throttle cable:


This limit switch is *clearly* broken; it isn't rubbing up against the detent in the throttle cable housing, AND it is completely disconnected.


There are two green wires that aren't attached to anything (one is green/wh stripe). Are these supposed to attach to this LS? Also, can I replace the LS without replacing the entire throttle cable assembly??


Are these the right wires for this Limit Switch?


Thanks!

Brad

 

I ran into the same situation and it seemed like the movement of the cable was supposed to trigger the action of the micro switch there. I was all proud O myself when I replaced the micro but not so much at my ability to understand, coax or witness the cable itself to engage the switch... I'm hoping someone with a HELL of a lot more knowledge than me with help me see the light, too.

As for the wire colors, if I remember right (which could be flawed) is that either way is ok at the switch.

 

It's a troublesome arrangement.

The spring loaded cable is designed to close the kickdown switch after WOT has been reached. If everything is up-to-snuff and perfectly adjusted a little 'bump' on the cable presses against the arm of the switch to close the circuit.

Have a helper in the cabin press the throttle to the floor. You should be able to see the little 'bump' appear via a slot in the cable. You can also see the spring mechanism inside the cable.

The cable can stretch with age, preventing the last couple millimeters of 'pull' required for the 'bump' to operate the switch

On my XJS one of the nylon bushings at the throttle pedal pivot had broken. This created a 'lost motion' situation where the cable was not being pulled enough for the 'bump' to operate the switch.

I recently had to replace my throttle cable on my present V12. The new cable is 'supposed' to be correct but I simply cannot get the adjustment geometry to work so I went to an alternate method of operating the kickdown

Cheers
DD

 

Hi Doug... I don't mean to insert my own stuff here but it's connected relevant if not the same...

In the few miles I have put on Cherry Pie,,, when I do hit the gas I have been impressed at the reaction of the transmission which does drop down a gear,,, then returns to the upper gear after what seems like a pretty close to perfect stretch of time. Is that the operation of the kickdown switch mentioned or is that the (I can't remember the name of it) vacuum diaphragm/switch on the LH lower side of the trans? The one connected to the intake via vacuum hose... Lol, or neither?

 

Changing down at moderate/3/4 throttle is the gearbox doing its thing via the vac tube and modulator. Flooring it at the pedal to produce an immediate sharp downchange is the kickdown switch.

 

Greg is right, of course.

Back in the day one of the things that made the TH400 such a marvel was a feature known as 'part throttle kickdown'. This feature allowed a 3-2 downshift, dependent on engine load, over a fairly wide band of road speeds without going to wide open throttle. This was very useful when climbing a light grade or overtaking slower traffic when you wanted a bit more oooomph but didn't want to go hog wild.

Other transmissions of the period were 'full throttle kickdown' only.

Cheers
DD

 

Once again... Thank you both for the valuable clarity and worked for experience. Thank you!

 

Let me loudly second what JayJagJay said!! Thank you for sharing your saged counsel, advice and experience!!!

Brad

 

I had the same problem with the kickdown switch. In the end I was tired of pressing the accelarator pedal through the floor to activate the kickdown switch. I think I found this solution on the net somewhere. I relocated the switch to be actuated when the trottle mechanism is fully engaged. Instead of the original design you have to fully engage the trottle mechanism and then press even more to get the cable mechanism to move. I attach some pictures. And the cables connected to the switch is green and green/white.

 

Smart!!!
How long will it take me,,, to think as outside the box 😆