When going off the line or launching at full power and good traction, with TC on or off - the launch is like a short bang bang bang bang stuttering jerk -- It'd exactly like an old yank car with Axle hop - is this normal?
Is the TC/DSC coming in and applying braking to the wheels...or is it actually axle hopping?

 

This thing shouldnt have a noticeable hop like that...not on normal tires anyway. Pretty even with sticky DR's on it wouldnt be bad. Ive launched mine hard quiet a few times with and without TC and no hop, the rear just goes a bit sideways thats about it.
You might want to check for something being loose down there.

 

+1 - only done a few launches and there is no hop, just a lot of tire spin with my previously bad tires. New tires just hook and go with a bit of wheel spin.

 

Never had wheel hop, and I go to the drag strip regularly. A friend with an XFR does get it pretty bad sometimes, though.

 

I have gotten something that felt like wheel hop occasionally in my XKR. I have 18" wheels so more tire profile, plus the shocks are old, so that could be contributing to the bounce.

I have heard of XKRs breaking the pinion gear, and wheel hop would be a sure fire way to do that, so it lends a little credibility to the idea.

 

I'll have a look to see if i can see anything "loose" , I have heard a rattle or a thump when going over bumps... I think....
How would I test if a shock absorber is faulty? My car has CATS

Really manifests itself on violent type launches , like me holding the car on the brake and revving to 2000 or so and going WOT...
Does the JAG turn off TC/DSC entirely when turned off or does it implement TC when it sees violent wheelspin as a sort of "nanny" system?
Does it have some sort of system that not only retards etc , but also does wheel braking to enable TC?

 

It'll stay part on. Yes it'll brake individual wheels. Also can demand reduced torque in which case PCM backs off power.

 

Thanks all for the help so far
So could the TC coming on , even tho switched off , apply braking to the rear wheels to give that juddery axle hop feeling?
Anywhere I can find out the strategy of the TC/DSC etc and exactly how it works?

 

In a WOT launch without first holding on brake the car should spin the tyres so I never heard anyone even bother with the brake and rev stuff.

I'm fairly sure most car makers don't publish detailed internals and Jag are the same.

You sound to have a suspension fault, I guess wear. If it bothers you it's going to cost to replace parts.

 

AFAIK the DSC in the STR is the same as the XJR (since the ECU and the rest of the drivetrain is the same) and I can tell you that with the XJR when you switch it off, it's completely off.

So i'm inclined to think there is something loose in your rear suspension, it sounds mechanical to me...

 

Multiple people have pointed out that the STR TC/DSC is not fully off when off and moaned about it so I'm doubtful that they could all be wrong.