Thanks Robbie, very much appreciated- in a way it is reassuring to know the issue is an oddity.

I've always favoured the software glitch or dodgy sensor hypothesis but appreciate the dangers of having a fixation on one thing and then missing the real cause.

A mechatronic leak - releasing pressure: well it shouldn't be that because I had the mechatronic removed and checked on a test rig but doesn't mean there isn't still a fault I guess?

The stator bush: the thread you linked to gave a VIN range for the TSB and my vehicle is not in that range. And if it was a mechanical problem wouldn't it have worsened over time? (After over 20,000 miles it hasn't got any worse).

So far I have been to three gearbox specialists and had fluid changes, software updates, new torque converter and as mentioned above the mechatronic check (note that the latter didn't include a TCM check as contrary to common belief they can't be tested off the car?).

The first specialist (Bristol Transmissions) who updated the software, suggested fitting a spare TCM but I haven't tried that yet.

On your suggestion of extended logging - well I have an opportunity to do that this weekend as I'm doing a couple of 1.5 hour hauls. Any suggestions for what I should be logging - or same as last time?

There is however a bit of a pattern to it. The first jolt always seems to coincide with the engine getting up to full operating temperature and then the next one will be something like 20 miles later (if cruising on motorway). 2008 MY Java Black TDV8 HSE

I didn't know that you had taken it to Bristol Transmissions as my humble knowledge is eclipsed by their expertise; they are a good bunch who I have learned loads from. They know this box inside-out.

One of the chaps I spoke to may have discussed it with Bristol Transmissions too... it is a small world when it comes to the more interesting issues.

 Land Rover - Turning Drivers into Mechanics Since 1948

How To - Battery & Quiescent Current Drain Testing

Free Fault Code Reading For Established Members:
Defender, FL2, D3, D4, Evoque, RRS & FFRR

Paddi, it might just be that this shunt is a "ghost in the machine" - a little foible that you never get to the bottom of.

Mine has strange tyre wear - no amount of alignment checks, adjustments and parts has sorted it. It appears to be just something mine will always do. Perhaps your "clonk" is yours...  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Paddi wrote:

There is however a bit of a pattern to it. The first jolt always seems to coincide with the engine getting up to full operating temperature and then the next one will be something like 20 miles later (if cruising on motorway).

The TC mode does change state when it has finished helping to heat-up the oil and it also allows the use of 6th gear too. The use of cruise control also changes the TC mode and strategy.

 Land Rover - Turning Drivers into Mechanics Since 1948

How To - Battery & Quiescent Current Drain Testing

Free Fault Code Reading For Established Members:
Defender, FL2, D3, D4, Evoque, RRS & FFRR

RRSTDV8 wrote:

Paddi, it might just be that this shunt is a "ghost in the machine" - a little foible that you never get to the bottom of.

Mine has strange tyre wear - no amount of alignment checks, adjustments and parts has sorted it. It appears to be just something mine will always do. Perhaps your "clonk" is yours...

Point taken - but I'm not prepared to give up quite yet as there are other live values to be investigated.

Last weekend I recorded another log whilst cruising along on the M25 and M2 and this time selected live values for:
Accelerator position (2)
Coolant temp
Engine RPM
Actuator supply volts (solenoids)
Solenoid 5 pressure
Solenoid 6 pressure
Torque converter
Transmission current gear

The full pdf is here:

http://www.rrsport.co.uk/gallery/albums/us...35_Log.pdf

and a snapshot of one 'jolt' episode at 990 seconds is here:

Click image to enlarge

On this log there two jolt episodes (TCC changes from closed to open to regulated and back to closed) at 990 seconds and again at 2063 seconds

It is interesting that the actuator supply voltage is steady at about 13 volts but momentarily spikes to zero one second before the TCC unlocks.

Solenoid 5 and 6 pressures are erratic all the time but drop to zero on the jolt.

The accelerator position looks erratic even though I was holding the speed pretty steady (as can be seen by the steady RPM)

One little detail to add is that on the return journey I used the trip meter to measure the distance between jolts and it was 20.3 miles between the first and second jolt and 20.1 miles between the second and third which is remarkably consistent n'est pas?

What is rather frustrating is not having any 'control' data with which to compare the logs I am seeing so hard tell if this is normal or abnormal data.

Going to press on and record some further values not tried yet and them maybe, as Robbie suggested, take the information along to Bristol Transmissions again or my nearer specialist who are known and respected by Bristol. 2008 MY Java Black TDV8 HSE

There is a one second gap in the gear selected line at the moment of the 990s jolt. Not sure if that is an artefact of the data plot or an indication of a cause. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Paddi wrote:

Thanks, perhaps disconnecting them wouldn't help much then.

As they say in all the best magazines: regular readers will be aware of my strange drive line shunt that occurs when on the open road just as the engine reaches full operating temperature and then again about 20 minutes later and after that at longer intervals if at all.

Monitoring the live value for the TC reveals that the shunt coincides with it unlocking momentarily.

I've replaced the brake light switch, TPS, engine oil temp sensor, torque converter and battery. The MAF sensors can also tell the ECM to unlock the TC it seems so the hypothesis was one may be sending spurious values. If that was true then maybe disconnecting may stop the shunt even if the engine runs a little rough.

My shiny new upgraded IID Tool (now BT version) just arrived so new plan is to record multiple live values and look for a spike coinciding with the shunt.

BTW the car runs perfectly with smooth gear changes the rest of the time.