Over the years there have been various mods to make the transmission kickdown a bit more lively....or make it function at all.

I've used the enrichment switch to activate the kickdown but it's a bit too aggressive. it seemed Ok on my XJS but I didn't like it on my Series III sedan.

More recently I've used a vacuum/electric switch and is was fine....but lately had become inconsistent.

Now I've tried something different and it was pretty simple. It's really just a duplicate of the enrichment switch arrangement, using a new bracket and switch (items #1 and #2 in the illustration) but located on the opposite side of the throttle capstan...across from the enrichment switch

https://parts.jaguarlandroverclassic.../brand/jaguar/

As you know the enrichment switch arm rides on a flat segment of the capstan and is 'bumped' into operation when it hits a curved part. The same idea is used with the kickdown switch. You have to decide where on the capstan to grind away a flat area and where to provide a 'bump' to activate the switch. This is pretty easy to figure out with the capstan on the workbench with the bracket and switched attached with small bolts. A few minutes of grinding and you're good to go. I have mine set so the kickdown occurs at about 90% throttle. The original cable-mounted arrangement requires 100+% throttle. The enrichment switch more like 70%.

I'm happy with the results but there is one caveat......

We're all accustomed to the generic lever-arm microswitches. I have a whole bag of 'em that I bought for $2-$3 each. However, these cheapies will not hold up to V12 engine bay heat. After just a few days the 'action' of the switch had gone soft. I rummaged thru my boxes of goodies and found one that looks and feels more robust. Fingers crossed that it holds up.

I wonder if it was engine bay heat that made my vacuum/electric switch become a bit 'iffy' in operation?

Here's a pic of the final result:



Incidentally, the kickdown switch also triggers a relay to cut-out the a/c compressor. After all, when you really give 'er the boot you don't want drag from the compressor holding things back, right?

Cheers
DD

 

my TPS switch 26yrs ago! a simple(from Radio shack aint no mo), volume control 270* ,cost $3. dollars!
works just fine and kick down is TV (throttle valve) cable, also set shift speeds!
gotta do what you gotta do, back stuff from Jaguar cost 1000% more and gotta wait months to get!

works for me!

 

this is great.

 

Changing the kickdown switch activation really transforms the car. I have chosen to activate it bit earlier than you but there is little worse than waiting for 100%+ throttle to get a kickdown.