My 2005 S-Type 4.2 with about 115kmiles runs just fine, no knocks bangs, squeaks or rattles, and accelerates up to my normal freeway cruise of 85 - 90 mph. But once in a while (every few weeks), as I am accelerating normally (not flooring it, just a nice normal throttle), the car hesitates, as if I pulled the handbrake on (if there was one), and a distinctive fairly high pitched sound comes from somewhere. Folks in the back say it seems to be under the back seat but it doesn't last more than a couple of seconds. To me it comes from somewhere behind me, I can't say where. The car definitely slows down, but not dangerously, just a clear hesitation. Then within 1 or 2 seconds (it seems like a lifetime cos it gets the adrenalin pumping) it behaves as if nothing happened and continues on up to speed.

Any ideas on what it might be, or how to proceed to diagnose it?

Thanks...

Dave

 

 

Have you ever done a transmission ATF drain-and-fill?

 

Might be worth putting the car in the air and looking / poking / moving / spinning things in the hope of figuring it.

 

I have an '04 XK8, but am researching the S-type (just about ready for a smoother ride). The 6-speed transmission is designed to have overlapping shifts (for smoothness) - instead of the lower gear disengaging before the next higher gear engages, the lower gear stays partially engaged as the higher gear engages, as in a progressive hand off. Now and then 4th gear stays engaged too long in my car when shifting to 5th; the result is two gears being engaged at once and, as you might imagine, it ain't pretty. It lets out a loud squall (that's the 4th & 5th gear clutches slipping violently) and the car slows dramatically. After about a second, 4th gear finally lets go, 5th takes over and all is normal again. This might happen once or twice in a week, then not again for some months, during which time the transmission works more or less flawlessly. This is with Sport mode engaged - if Sport mode is de-selected, it happens much more frequently (needless to say, I keep it in Sport mode). It sounds to me like you may be experiencing the same sort of problem.

 

Thanks, Volbrewer,That sounds like the culprit! Thanks!! Now the next question would be what can be done about it....

 

See post #3.

 

Thanks, Mikey, I was assured by the previous owner (6 months ago) that he had recently had it done, but I'll see how easy it is for me to do it. Hopefully that's all it will take to clear it up -- but as it happens so infrequently it will be tough to be sure of the fix... worth trying though.

 

its not simple ! but there are many how to threads to follow .
i cant help wonder if it has the correct fluid or fluid level also .

possibly may require a trans re-flash or a trans adaption reset .

also the park brake motor is beneath the rear seat kind of.
could it be self activating ?

 

A friend & I changed the fluid/pan/filter in mine (using the genuine ZF fluid). He had a lift, but we still found it a daunting job (I can't imagine trying to do it on jack stands). The trans has to be hot to do the job, and the engine needs to be running. The hot exhaust pipe is a couple of inches from the fill hole, which makes it extremely challenging to do all the stuff that needs to be done at the fill hole. BTW, there are two kinds of trans pan bolts; one is T-40, the other is smaller, maybe T-27. The Torx fitting on the bolts that use the smaller tool size is extremely shallow, which means the odds are quite high that you will strip a few of the heads out. We had to slot a couple of the bolts using a "ziz wheel" to accommodate a large flat-blade screwdriver to get the bolts out (the heads are too thin to grip with Vice grips). I strongly advise checking the bolts ahead of time and ordering T-40 replacements before you start the job if your car doesn't have them. Having done the job once, I'll farm it out next time! The right tools (including the factory rig with the temperature probe), a lift, and experience are worth paying for - it's a tough, demanding job and you won't want to wonder if you got it right. Also, the fluid change did zero good - no change whatsoever. I've never had my trans reprogrammed because I really don't think it would do any good. I think a shift solenoid is hanging. I had a diagnostic run on it and it showed nothing, which implies that the computer is OK. OTOH, why does mine act up so much more when it's not in Sport mode? Sure smacks of a computer issue. But I still think it's mechanical/solenoid issue. Pretty affordable kits are available for rebuilding the valve body (new seals and solenoids); rebuilt valve bodies are pretty steep. Either way, it's a lot of work and I'm sure it's not for the faint of heart. I've decided to live with it and hope for the best. Thirty-five kmiles and counting so far; still doing OK (115 k total). Eriksson Industries wanted $2700 for a rebuilt three years ago; not sure how much they are now.