I've just taken my XJS home after a couple months at the shop, and noticed on the way home that the car doesn't shift like it used to. It'll hold first until about 40 mph and 4,000 rpm at which point it will shift rather abruptly (though smoothly) into second, and hold it with no complaints.

I got curious and accelerated onto a highway. Under a heavy foot the shifts were quick and smooth, though still noticeable, and I was able to get all the way into third.

The fluid is clean and full - bright red with no unusual burnt smells or foreign matter. It is rather cold at -7f and getting down to -12f or even lower tonight.

I guess the root question is - where should I look first? Searches have uncovered some pretty apocalyptic scenarios, and I'd like to think that I didn't just jump out of the frying pan and into the fire.

 

Don't get too worried at this point.

Might be as simple as a modulator failure. But first make sure that the vacuum hose to the modulator didn't break or fall off.

Cheers
DD

 

as above


also check the electrical kick down switch wire on the opposite side to the modulator ,

but its more likely that it has come off in the engine bay , presuming its a V12 ?

like Doug say , don't panic just yet , they usually get very noisy and troublesome before falling over

BB

 

Thanks for the input

If I were to try to rule out the kickdown as being part of the problem, what would disconnecting the wires to the kickdown switch under the hood do for me? I have yet to take a closer look at, but tomorrow is looking to get up to near freezing, so I figure that would be a good time to go crawling under the car.

I'll have a closer look at that modulator too. I've got a spare, but it still should be solid.

Edit Loose vacuum line to the modulator. Had me worried for a bit though

 

Disconnecting the kick down switch would eliminate it's affect on the transmission. On my 78, the kickdown switch is on the throttle cable, just before the bell crank. The cable has to slide back and forth, about 1/4" against a spring to activate the kickdown. Mine was stuck in the no kickdown position, but if yours is stuck in the kickdown position, it will give the symptoms you are experiencing.