My 2004 XK8 convertible has 2 problems which I wonder might be related to one another.
1. When cold and cruising in the 30 mph speed range at constant throttle and light load in D gear, there is a slight rpm oscillation of about 50 rpm.
The oscillation persists for about 10 minutes of drive time, then ceases.
The oscillation ceases when any lower gear is selected, but returns when D is re-selected (until the ~10 min).
These oscillations produce essentially no sense of acceleration/deceleration.
2. As well, after some spirited driving in our local mountain roads, including the use of manual shifting, there may occur some random events of the famous XK8 transmission chirp, in my situation usually, but not always, on full throttle downshifts.
Can someone enlighten me as to the cause of each of these conditions, possible overlap, and to potential fixes?

 

Mine 2003XK does the same.. from what i have undestand from sifting through a few threads here, is that its a matter of making sure there is no wacuum leaks and that the throttle body is clean and nice.

...else, its suggested that it is a matter of a tired? Converter... makes kind of sense since no faultcodes what so ever is showing up.. its too fun to be out on the roads as for now, so i am goin to deal with it later.. its somewhat annoying but i can live with it..

Maybe someone here at the forum has the imformation regarding the exact cause..

/E

 

At 56k miles I'm hoping that the torque converter should not be failing, but who knows!

Frankly, I'm more concerned about the occasional chirp noted on some upshifts, but mostly on full throttle downshifts.

 

My 2003/04 model year has done this since I've owned it. I think it's somewhat normal behavior as I have seen a lot of 6HP26 do this on various different cars. No idea exactly why it happens exactly but if I had to guess it's probably to do with the fluid not being up to temperature? Even after a rebuild I've seen some do it still so it's probably OK? The chirp is odd though, I know you can get an additive for the fluid to prevent of dampen that sound.

 

I'd start by having the gearbox oil changed. Have it done at a ZF specialist, as they are able to perform a complete flush that includes converter & heat exchanger oil.

 

Search the site for 6HP26 squawk. Seems to be a common problem with these trans. Solution seems to be a fluid change and some Motorcraft additive.

 

ZF6HP26 through the years.

 

Given a persistent occasional "squawk" on some shifts, and given the uncertainty about the inclusion of the "early prescribed additive" in modern Lifeguard 6 ATF, is there a currently recommended additive to address this noise?

 

With the special additive no longer available, the best alternative is probably just a typical ATF drain-and-fill with Mercon SP. Be aware that ZF tech support has long stated that the squawk is just a noisy nuisance. No harm is done to the clutches....

 

Perhaps you can try the additive I used on my 2003 6HP26 squawk. it was a Ford Motor craft kit XL 16 KIt. Ford used the 6HP26 as their 6R80 design by license from ZF. They had this SQUAWK problem thru 2013 and developed the XL16 additive kt. I eliminated my noise and just google it and prices from $60-$100. Got mine from a Texas ford dealer.

 

It's good to hear that the "squawk" isn't an indication of damage occurring, or of impending doom.

 

Following an ATF replacement and filter change the occasional squawk persisted. While care was taken to fill the transmission per the heat measurement technique, I decided to recheck the fill level. This about 100 miles after the service event.
I discovered that the transmission was about 700ml low at 25*C. I have not determined the cause of this shortage. Be aware.
I left the plug out to observe the difference/overflow as it climbed to 30*C. There was only very slight overflow. Hardly enough to care about toward the process.
Since this fill revision there have been no more noises and shifting is nominal in or out of Sport mode.
The ATF used was TOTAL Energies brand LV/MV
-which is labled - ZF Lifeguard 6 specification

 

I'd be rather concerned about using a fluid that claimed compatibility with Lifeguard6 (ZF 6HP26) and MB236.12 ( Merc 722.6 - 4.0L XKR), as well as Mercon LV.

 

What is the concern? Lifeguard 6 is the ZF spec for this transmission.
I recall the days when there were arguments about the reality of multigrade engine oils, then there was the concern about the viability of synthetic engine oil. And there's always the proposition of additives providing some kind of magic that the oil companies have left out, for some strange reason. Still the forums are full of arguments about which is "the best" engine oil. My thought is that if the automotive fluid in question is made by a reputable manufacturer and it claims a specific SAE or other generally accepted standard, it is likely to work properly when it is specified and installed to the hardware manufacturer's specifications.

 

It was not my intention to create another 'best fluid' debate, as it's clearly the one specified by the transmission manufacturer.

My concern is the differing specs & chemistries for each type. For example, compatibility is claimed for both Mercon SP and Mercon LV. The latter is a low viscosity fluid, SP isn't.

Valvoline makes similar claims - see this post from Don B:
https://www.jaguarforums.com/forum/x...5/#post2313182

It may work and I sincerely hope that it does, but since the trans is the second most expensive part of the car, it's a lottery ticket I wouldn't buy.

Just my

 

Fair enough ! 👍