When comming to a complete stop, before the car stops there is a slight jerk..... almost like it is downshifing, If I put it in N while coming to a stop it doesnt do it..... any reason why it would do this?
Thanks

 

It's a known characteristic of the ZF transmission which both ZF and Jaguar refuse to accept as a fault. It feels a little like the car has been tapped on the rear bumper just as you come to a stop. Annoying but said to be normal.

However, the ZF is such a good transmission, one of the very best in the World, we forgive this minor fault.

If it is this fault then it is intermittent, not every time you roll to a stop will that little kick occur. It is the transmission downshifting into second gear that does it.

 

I have the same occurring with mine. However, the slower you come to a stop, the less likely it is to occur as the downshift is most noticeable from 4 down to 2 with a bit of firm braking.

 

That's interesting because that is the opposite for me. If I slow down quickly, I feel nothing from the transmission in regards to a clunk or hard shift. When I am coming to a stop slowly, it shifts hard on the last gear.

 

For comparison, I've never noticed any issues slowing to a stop in regards to a jerk or downshift. The brakes are a little too good so it's hard to come to a nice clean stop without a little bit of a jolt but it isn't trans related. 2009 XF Supercharged.

 

There's definitely a little thump issue with the ZF transmission unrelated to braking. This has been around for years and affects not just Jaguars. However, not all ZF transmissions do this. Either way ZF says it isn't a fault.

 

Here's probably why this little thump occurs in these transmissions as you roll to a stop.

There is a two stage internal torsion damper (two sets of coil springs like the damper springs in a dry clutch plate). These wind up and unwind in response to driveline torque variation. If they happen to be tensioned or compressed as the lockup clutch releases then you likely will feel that as a thump or lurch in the drivetrain.

http://www.zf.com/ap/content/en/japa...converter.html

Click on the link at the end of this page and then watch the video at the "operation" tab.

ZF Friedrichshafen AG | Product Overview | Cars Torque Converter

Apologies if this link doesn't work, it worked twice for me then stopped working. Maybe if you access the ZF site directly and go to the link it will play.

 

Nice post jagular.

If I understand this correctly, the "spring powered" lockup clutch is used instead of the typical transmission fluid-based power in the TC for quicker engagement and to help reduce wear and tear (instead of using hydrodynamics all the time like many classic transmissions).

Makes sense why this is a perceptible change that results in a bit of a "jump", as the transmission is temporarily powered by a mechanical "spring buffered" connection instead of a fluid powered connection.

 

Well, sort of. The torque converter handled drive forces during the shift. The lockup clutch locks out the torque converter after the shift is completed. This lockup clutch releases as you roll to a stop and the transmission selects second gear for the next start up. This tranny always starts off in second gear unless you nail it on getaway, only then does it downshift to first. To really get going you must manually select first. Then the torque converter stays unlocked until second gear is reached.

Since the torque converter just idles for most of the time the transmission fluid inside it doesn't wear or breakdown. It can be made smaller and lighter as a result. The lockup clutch delivers all of the drive most of the time, and returns fuel economy and performance comparable to a manual shift. This is why Jaguar feels it is ok to fit this tranny to the new F Type. I just found out that the 8 spd is 3 kg lighter than the old 6 spd. Also, it is 5 kg lighter than VW DCT box! Also, the ZF automatic can handle twice the maximum torque of a DCT: 700 Nm as compared to only 350Nm. No wonder Jaguar fits the ZF in preference.

I think the two sets of springs are dampers and wind up and release in harmony with the flywheel oscillations, complementary harmony, and cancel out any vibrations except occasionally, as when the car rolls to a stop. It's not perfect but it's pretty good.

 

i know this is an old thread but i wanted to give a little input WRT my experience today. this thread and a half a dozen others on this site (some XF, some not) discuss similar thumping sounds upon stopping. i've had my '12 XF for a few months now and have been experiencing the same thing. like all good hypochondriacs, i read the threads and worried that it was a suspension or transmission issue which needed to be addressed sooner rather than later.

i took it in today, demonstrated the phenomenon for the tech and left. at the end of the day they said after a thorough inspection and some head scratching they contacted the manufacturer who said it was fuel sloshing around in the tank. they were aware of it and would have a tech bulletin and fix in between 60 and 90 days.

i have no clue whether any of that is true, but am passing on the information for your future reference...

 

Fuel slosh is a known characteristic of the XF. I am pleased and surprised Jaguar now says they can fix this.

 

Good to know. I've noticed it a couple of times on my '12 but not enough for it to be a concern or bother. If it's not too intrusive of work, maybe I'll have them do the fix next time it's in for routine maintenance.

Thanks guys!