Hi All

Can an XKR 2005 transmission be fitted into a 2003 4.2 XK8?

Are they the same or are there incompatible differences?

Any advice would be much appreciated...thanks.

Andrew

I believe they are the "same" in general terms (ZF 6HP26), so I believe they should be a mechanical match. Now, the control unit for these transmissions is built-in the valve body, so in the off chance the software is different between the XKR and the XK8, the XKR software would be transferred to the XK8 as well. I suppose the dealer (or someone with dealer software tools) could likely reflash it, reset adaptations, and the like if necessary.

If it was me, I would try and get a picture of the identification plates on each of the transmissions. They usually convey detailed build information beyond simple model number as these transmissions, like most everything else, go through revisions in their life cycle. I would then try and reach out to ZF for assistance, armed with these technical details. ZF technical support is reputedly very helpful even to us lowly owners.

If you don't mind sharing, what is making you go down this path? These transmissions have earned a reputation for being generally reliable, and some folks have sometimes been talked into a replacement when the root cause ended up being elsewhere.

Best of luck, keep us posted.

Thank you fmertz for your reply.

I hadn't considered the software side of things which you quite rightly point out could cause issues. I may indeed contact ZF for their advice.

Whilst these gearboxes can be reliable, they do also suffer from annoying issues such as the infamous "lurch". This is the problem with mine. I recently had the fluid and sump+filter changed, but it actually became slightly worse afterwards.

I believe that a replacement of all seals in the valve body plus possibly replacement of solenoids can cure this..but by the time you buy all the necessary parts + fluid and labour...it work out quite pricey. That's why I was looking for a replacement gear box.

Maybe I will go down the refurbishment route after all.

Kind regards

What fluid did you end up using? Some here swear by Mercon SP, instead of the ZF LifeGuard6.

Another path is to re-set the software adaptations to force the transmission to re-learn its condition with the new fluid. Some have had great results with that. Typically done at the dealer, for an hour labor, or for a diagnostic fee.

I used Valvoline ATF. I may try the dealer with that info and see what they say....thank you.

I have also just written to ZF for their advice....thank you for that suggestion.

I concur with an ATF drain-and-fill (I use Mercon SP) along with having the ZF adaptation cycle software re-flashed by a competent dealership. This process has restored the shift quality in my wife's 2006 XK8 on two different occasions - once back in July 2013 and most recently this past April. Her XK8 is now approaching 106,000 miles. Rick (joycesjag), Wayne (cjd777), and I are doing one final ZF drain-and-fill tomorrow (again using Mercon SP) just to get the mix of Mercon SP vs. any old remaining Lifeguard 6 up to about 85/15. After we're done tomorrow morning, I hope to never have to fool with this ZF again during the remainder of our ownership period. Time will tell....

Are you positive this fluid is rated for this transmission? Only a handful of fluids have been tested and approved, as far as I know: ZF's own LifeGuard6, the Jaguar branded fluid, and Ford's Mercon SP. As usual, these fluids are made to a spec, and it is quite possible other brands offer fluids to the same spec. On the face of it, Valvoline is not a popular choice on this forum, but Jaguar is not the only brand that fitted these ZF transmissions either. I would not know what is recommended for a BMW or Bentley I suppose.

When I wrote to Valvoline, they said that their ATF was suitable for the 6HP26 gearbox.

However, after reading what other members are using, if I decide to change it again...then I might well go for the Mercon or Lifeguard.

Thanks for all the advice so far.

There is a fairly big price difference, and, for once, the cheaper Mercon SP seem to have the edge in driver satisfaction on this forum. Can't speak for everyone of course.

Separately, as Jon89 pointed out, there is the issue that a standard flush-and-refill only flushes some (more than half) of the fluid, not all of it. Some picky owners perform several flushes over time to eventually flush most of the original fluid. Obviously, this points out to the general need of these transmissions to be maintained, nothing new really.

In short, in your situation, I would try and pursue a cheap fluid change and possibly an adaptation reset before a more expensive swap of the whole transmission. Have you checked for any Jaguar-specific codes?