2005 XK8, 4.2L 51k

hello all, my first post on here! I bought an XK8 about 3 months ago. Since then I’ve been noticing this clunking sound and feel all the way through the car when I’m slowing down to a stop when the car is going into first gear it seems.

This is when I’m breaking and also when the car is slowing by itself. I’ve read forums on here about possibly the valve body etc being faulty but I was wondering can anyone direct me or have they heard of this problem before

thanks

 

From my reply to the post above ,

When its in normal rather than sport it starts in second not first. You could try knocking it into neutral as you stop to see if that takes it away ( removes load on drive train)
Sounds like play in
1/ Drive shaft joints
2/ backlash in the differential ...mine has a little
3/ play in a propshaft joint.

All are easy to find if its up on a lift.
If its the differential dont worry too much just put some thicker oil it SAE 140

 

Could use a trans fluid and filter change. Mine went butter smooth afterwards. Look that up on this forum and you will find plenty of info. It's messy and involved but not too hard to do. Lifetime fluid is such a farce. Don't get me started. Research is your friend. Welcome to the forum. TM

 

^^ I concur. If you have no service history of a recent ATF drain-and-fill, that should be your first step. Many of us use Mercon SP ATF (available at any Ford dealership or online) as a much more economical alternative to the OEM ZF Lifeguard 6 ATF. Search this forum using "ZF 6HP26 ATF drain and fill" and prepare to do plenty of reading to get yourself up to speed on this issue. If you decide to drop the pan instead of doing just a drain-and-fill, be sure to replace the Mechatronic sleeve as well. The original factory sleeves eventually develop a slight ATF leak. The redesigned sleeves available for the past decade or so are more robust and do not leak....

 

Went through this a while back and documented my ~journey~. May be pertinent to your situation. Here ya go: https://www.jaguarforums.com/forum/x...estion-229263/

Hope this helps.

Mickey

 

yeah we put it into sport mode last night too, was non-existent / less noticeable. Not sure if it completely went or subconsciously I was thinking it was there because I’m so wary about it now. I’ll look into it. Thanks

 

That does sound like the known harsh shift issue, a.k.a. "The Lurch," that is usually resolved with a fluid exchange, preferably followed by clearing the Mechatronic adaptations and updating the firmware. Off the top of my head, the last update available was in 2006, so your car may not have the update.

Updating the firmware requires SDD with the pertinent update file, a suitable interface such as the Drew Technologies Mongoose JLR or Ford VCM, and a 50-amp power supply to maintain vehicle power during the update. The Mechatronic will eventually re-adapt to your driving style, but the process can be accelerated by following a procedure in SDD that usually takes an hour or so to complete.

See a fluid change DIY here:

ZF 6HP26 / 28 Transmission Fluid Flush DIY

Cheers,

Don

 

thanks Mickey, this is what I was fearing it would be. Seemed to only have developed in the last 2 months of having it. I don’t usually change parts out myself, neither would I feel confident to without the equipment. I think I’ll take it to my local transmission dealer

 

as a matter of course I always use 75w-140 vs the spec 75w-90 in the differential. It does cost more, nearly double, but has the advantage of reducing wear when the differential gets hotter as it does on long distance driving.

And as mentioned, some noise can be mitigated by using the 75w-140 product. Mobil 1 sells a high quality synthetic in both viscosities.

I changed the differential fluid when I first got my XKR @ 116.000 miles. Clearly it had never been done before . Changed it again 50,000 later. It wasn’t quite as bad looking, but definitely needed changing. I’m only going to go 40,000 miles on the current rear end fluid. As I’d like to live out the rest of the car’s life (and mine) on the original gear set.

Z

 

If you can get 140 EP thats the stuff .

 

Just throwing this out there - as I have the same issue on a 2004. It's worrisome and I have to know damage is occuring when I consider the weight of the moving car and the forces involved.

Can some of the 1-2, 2-1 issue have something to do with the signal from the throttle position sensor, fly by wire,,,, the info being sent to the trans about the peddle? If I peddle just right, I don't get the upshift clunk/lerch when taking off. My 2-1 is not so bad, the 1-2 upshift is my (real) worry spot.

 

The clunk you feel may be the torque converter unlocking. These parts have friction clutches in them and when they get worn, they can get a little rough.