Every once in a while, a few seconds after coming to a stop at a light, there is a rather forceful thud from the rear of the car, similar to the sensation of being rear-ended.

I suspect something to do with the transmission. Any ideas?

 

Hm... I don't know how forceful you are talking, but gas sloshing around in the tank tends to cause a lot of thumping sounds at low speeds, especially in stop and go traffic.

 

I think this may be the issue.

https://www.jaguarforums.com/forum/s...ad.php?t=46589

The tranny was reflashed a long time ago and an additive put in for the TSB regarding whooping sound. This new issue started about 6 months ago or so.

 

Mine does this too, it's the tranny. I just don't know what it's doing.

 

yah, the lurch, i'm dealing with it by keeping the car in sport mode, it almost never does it while in it. I'm hoping a magic TCM reflash will help, or a clearing of the memory with a hard reboot, then retraining the transmission will work...but I have yet to perfect the training drive cycle to make any difference.

 

Later S-types are famous for this- it's called 'the lurch'. Although reflashes are available, nothing cures it completely or permanently. I just changed my driving habits to compensate or avoid inducing it.

 

So this happens a few seconds after you've already reached a complete stop?

 

This isn't just a Jag moment, it happens a lot as wear and tear sets in. Here's what happens. As the powertrain parts wear, they develope "slop." My pick-up does exactly the symtom that you described. As I come to a stop and ease up on the brakes the vehicle rocks back. At the same time the trans is between gears as it is downshifting. Now the drivetrain has "unwound" and all the components are rotated back. Finally, the trans shifts into low or 1st and the slack is quickly taken up which gives you that jolt as though someone rear-ended you.

OF COURSE I ALWAYS CHECK FOR LOOSE SPARES AND STUFF IN THE TRUNK, ETC. FIRST.
Here's a test. Drive along a road without traffic. Just before stopping, put the trans in neutral and stop like you were coming to a signal. You should not feel the jolt. COME TO A FULL STOP BEFORE PUTTING IT BACK INTO DRIVE. You may feel a jolt when you go back into drive.

MY CAR TAKES ME FROM PLAIN NUTS TO ASSORTED NUTS!

 

But the OP says it happens after he's already stopped, which doesn't make much sense!

 

Wanna drive my S-type? Very common.

 

Haha, I guess I'm saying it's not common on other vehicles--a lot of people try to defend this problem by saying it's not just Jags. Sure, most automatic trannies kind of have a gentle lurch as the tranny shifts back into first gear as it nears a stop, but none of them have a "rear-ended" sensation a few seconds after stopping! This is a Jaguar issue!

 

That is correct.

It does not happen all of the time, for example it has been a few days now since it did it last. Sometimes it may do it twice in one day. I tend to drive very carefully, not agressively, but do come to relatively hard stops as the Brembo brakes tend to squeal under repeated light braking.

If I was going to guess, it seems like something is sticking and then disengaging abruptly.

I have had several late model Jags with ZF trannys as well as Mercedes with ZF and have never had this happen to me before.

The dealer of course can do nothing because since it is so infrequent I can't get it to do it for them. I am not sure that a reflash is the cure.

 

I had a new S-type R for 18 months before lemon lawing it, but it never had a tranny issue like this.

 

It's not only Jags. My Ford Ranger does the very exact same thing. In over 20 years as a mechanic for a big fleet, I saw this in cars, pick-ups, flat-beds with GVW's of 28,000 lbs, etc.. On the bigger stuff, you can look under the vehicle and see it happen. The big driveshafts make a big bell sound when they take up slack.

There is a lot that develops "space" during the wear and tear of use. You have ring and pinion gears along with side and spider gears and axle splines all getting space.

 

Since it Is a recent development, sounds like a tranny problem, is under warranty but hard to reproduce, how do I go about getting the dealer to fix it?

 

I'm not sure if I believe this "slack" theory. Do all of the cars that have this problem have high mileage?

 

http://www.thelurch.com/lurching_zf_transmission.htm

Better not tell this guy then

 

I have seen that site before.

Either I was "lucky" or maybe the problem isn't with new cars.

Either way, this is not the problem I am experiencing.

 

ZF had this to say:

The bump from behind at stops may be due to normal internal wear combined with programming not accounting for this wear. I recommend contacting your Jaguar dealer to see if any updates are available to address this. While some independent service centers claim they have the ability to update software only your Jaguar dealer has access to factory support as well as ZF support where all problems are researched. If a fix is available the dealer will make this recommendation. If a more serious problem exists your dealer will be able to diagnose this as well.

 

What a bummer. Most dealers would probably want to replace the tranny!