I noticed that, especially when the car is cold, getting off the gas results (in certain conditions) in the car holding whatever gear it was in for about half a second or so, then dropping down to a more or less idle RPM. This is often accompanied by a clunk. It almost seems like it's coming from the rear. I do not think it is suspension related as it doesn't seem to happen out of gear. Is this a common thing? I have learned to live with the thumping from the gas in the tank sloshing around, but this one is a little bit annoying.

I have also noticed that when pushing the cancel button for cruise control, it will often downshift one gear (seemingly) and hold that gear for about a second before going to an idling engine RPM.

I just had some service done at the dealer today (oil change, new thermostat, etc.), and they noted that the air filter is dirty, so I will replace that. In my old Lexus, that had a big impact on shifting (I guess airflow was restricted, causing the computer to get confused). I will try replacing this and see what happens.

 

Actually, it doesn't happen only on braking. Just sometimes when I get off the gas.

 

Also, noticed that on a quick sprint (WOT) from a stop to 35 mph or so, the transmission seemed to hang up at 3000 rpm after I got off the gas for several seconds. Is this typical? Perhaps the transmission is trying to anticipate additional spirited driving?

 

Well, nobody else notices this on their XJ?

 

clunk is probably a worn out trans mount or maybe u joint but prob trans mount.the cruise control down shift is prob common especially if your going down hill or depending on how fast youve got the cruise control set.

 

Transmission mounts and u-joints came to mind, but is that a common thing at 40k miles? How much can transmission mounts and u-joints be replaced for?

Also, I noticed that if I slam on the brakes semi-hard (suddenly without warning), I get almost a "shock" throughout the entire car. Maybe it's in my head, but it seems like the brakes are biting really hard and/or not in a gradual way. Is this typical as well?

 

Hi, just a thought, I had a similar problem with the clunking as you seem to have, my dealer did a reflash of the gearbox software and then I drove without using sport mode for about 500 miles or so , this enabled to gearbox to relearn driving style and the result was amazing, I have done more than 25000 miles since and the problem has not come back.
Speak to your dealer or independant about doing this, I think it cost me about £120 but was well worth it.
Good luck

 

Thanks for the info. I am thinking transmission mount, as there is also some level of vibration when I am on the highway and getting off the gas and coasting to a lower speed.

Any idea how easy it is to change the XJ transmission mount?

 

hi, sorry don't know much about the mountings but hope you get it sorted, I actually did not have any noticable vibration on my one.

 

The trans mounts are pretty solid on these cars. I've never seen the mounts crack, leak, etc. I would do the reflash of the TCM. Also I would have the dealer do a adaptation road test. Or you could drive it yourself and have it releared. Also, you have to make sure that the TCM can be reflashed, because if not, your just putting the same software back in, that already exists. Now a adaptation reset can be done, even if the TCM can't be updated. There are certain parameters that the dealer should go through in order to re-teach the transmission. The parameter reseting is impossible to do on the street. If the dealer had a dyno, it would be possible to shift through all the parameters, without having to take it out on the street to do the reset.

I'm not sure what vibration your talking about?

Also you said when it's cold, does it shift like this when the trans warms up?

 

It is a very faint clunking sound. It seems to happen at any temperature, but sometimes it seems more noticeable when it is cold.

As for the vibration, I guess it's not a vibration that I "feel", but there is kind of a low frequency (low tone) sustained noise that happens when I am coasting down from say 65 to 40mph in gear.

Will unplugging the battery for a few minutes reset the transmission?

 

i am a jag tech and i have never seen the trans mounts go bad on these. you might want to check and see if your trans pan and trans connector sleeve are leaking. these ZF's hate to be even a little low on fluid. Also have your dealer do a tcm reflash and adaptation clear

 

I get the clunk occasionally, with the same conditions you noted (letting off gas).

I also get the gas slosh noise, which I'm learning to live with, but I think is a shame.

 

I have had the exact same symptoms occur lately. Very soft clunk when letting off the accelerator at slow speeds along with an occasional humming noise when coasting up to a stop sign or light.
My car is under warranty and will be going in for service sometime soon. Any suggestions I can give the service manager?

brdave

 

I have no idea about any suggestions. But best of luck, and let us know what they say!

 

Could you describe the conditions that produced your knocking sound to me?

For me, it seems more like when the torque converter would be going in and out of lock-out mode. Is this something that could be fixed with a reflash of the transmission?

 

I think you may be experiencing the ubiquitous ZF Transmission "Lurch"

http://thelurch.com/lurching_zf_transmission.htm

According to my dealer they all do it......

 

Hmmmmmmm.... that S-type link shows that the guy replaced the torque converter due to a low-frequency "rumble/judder" at 50mph. That's similar to the noise I was talking about when coasting down from highway speeds!

Uh oh!

 

Well, I think an acceptable workaround is to use the sport mode on the tranny. I noticed no clunking or judder with sport mode on, although it does take longer to reach the higher gears. Clearly the problem is something with the shifting logic/software adaptation because it goes away with sport mode.

 

hi. I woul get the clunk sometimes when slowing down and then as the box would almost hesitate and clunk before engaging the lower gear , it would also happen if I had slowed for , say, a roundabout and then as I stepped on the gas the car would clunk as it pulled away. It was a jerky gear change. Not sure about when and what the torque converter was doing but can definately say after the transmission reflash the problem has not come back, and I have done a considerable mileage since. Best of luck and hope this helps.