The issue is a vibration accompanied by a sort of groaning sound when accelerating away from rest/low speed. It seems to be load related as if you accelerate gently it isn't noticeable but if you do it more briskly it is evident, though only briefly. With the caravan attached it is clearly evident.

In a recent test (with caravan attached) I put it in command mode and moved away in 1st, which was OK, 2nd where the symptom was clearly apparent and 3rd, which was OK. So it seems to be 2nd gear related.

I've spoken with Gary at TAS on Mersea Island (Essex) who seems well regarded in this field and he says that it's very unusual for an autobox of this type to have such a symptom in one gear only because of the way the Ravigneaux cluster works.

Having spent some time on you-tube trying to educate myself on this (always been a "manual man" previously) I understand where he's coming from when he says that. So, we seem have a "it can't do that" situation - except it is doing it.

does anyone have any ideas that might help us pinpoint the problem?

I saw a chart on a you tube video that showed the elements involved (Sun, planet carrier) & what's braked for each gear but I can't find one for this particular box. That would useful information if anyone knows? 2008 TDV8 Vogue

Sounds like it could be the torque converter to me. The 2nd gear only occurrence is interesting, but thinking that could be related to the TC maps used? Would also be affected by Command Shift.

What mileage? Has the fluid ever been flushed/changed?

Quote:

I saw a chart on a you tube video that showed the elements involved (Sun, planet carrier) & what's braked for each gear but I can't find one for this particular box. That would useful information if anyone knows?

LR's Description and Operation section on the 6HP26X in the D3 here may be of interest: http://www.disco3.co.uk/gallery/albums/use...ration.pdf

More docs in bbyer's gallery too: http://www.disco3.co.uk/gallery/thumbnails.php?album=5059

HTH  Visiting from DISCO3.CO.UK
Discovery 3 TDV6 Auto HSE Zambezi Silver

Many thanks LfW. The description & operation doc is really useful.

It's a 2008 with 82K on the clock. Changed the oil (drained, new pan, filled, run, drained, filled) about 1,000 miles ago. Interestingly I'm pretty sure that the symptoms are less evident since that's been done. Not an instant change. A slight improvement over time.

Now I understand how the gear clusters work I'd been wondering if the problem might lie in a clutch, hence looking for the "what's used in which gear" info.

Having read through it I notice that Clutch C (which locks the sun gear 2 of the ravigneaux cluster) is only used for 2nd and 6th gears. The only difference between these two gears is that in 2nd the drive first goes through the simple planetary cluster before being applied to the ravigneaux cluster while in 6th the drive effectively comes straight from the TC output. overall ratios are 2.340 (2nd) and 0.691 (6th).

My sums tell me then that the planetary cluster is delivering a reduction ratio of 3.38 to 1. If the output speed is reduced the output torque is increased so in 2nd gear clutch C has to resist 3.38 times the torque that it does in 6th.

Could it be that it slips, causing noise & vibration, in 2nd but can cope without slipping in 6th? 2008 TDV8 Vogue

Are there any faults on the box? I'm no expert on it, but I would have thought a fault code (incorret gear ratio?) would be stored when such issues in the box itself occur - and possibly limp home mode. Are there any actual shifting issues?

The normal failure that occurs within the 6HP26 is as a chain reaction initially caused by TC failure (due to lack of a fuid change). This essenstially kills the whole box due to heat and contamination, burning the friction plates. AFAIK, failures within the gearbox are pretty (very?) rare outside of these circumstances, but obviously, that's not to say they can't happen.

Your symptoms are still sounding in line with those normally experienced with TC failure. Like many others, I experienced judder (cobblestone effect) at around 35mph (some experience it slightly lower/higher) and it developed a whine on acceleration, plus a bit of a clunk on taking up drive, but it was fine at higher speeds. The improvement with fresh fluid would be consistent too.

 Visiting from DISCO3.CO.UK
Discovery 3 TDV6 Auto HSE Zambezi Silver

No fault codes & no shift probs.

I'm trying to get my head around how a TC prob (i.e. engine speed) can give a symptom at a one road speed. But I guess if it did - it did! This occurs at about 15 - 20mph I'd say.

I don't have any variation in revs at a given road speed that would indicate TC slip.

I do get a soft "bump" when setting off after having come to a standstill which I put down to a bit of slack in the drivetrain. My (manual) Jeep did the same thing. Slowing down - car is pushing engine, accelerating away - engine pushing car & there's a lot of drivetrain between engine & wheels on a 4x4. Does this sound like the symptom you had & did it go away with TC work? 2008 TDV8 Vogue

Quote:

I'm trying to get my head around how a TC prob (i.e. engine speed) can give a symptom at a one road speed.

It is slightly odd, but these boxes are so complex, with the many different maps and modes for it to choose from mean that problems can appear quite different, and of course, the adaptive nature means no two boxes are the same!

As the problem develops, multiple judders tend to occur in different gears/at certain speeds. TC lock-up behaviour varies between gears, as well as different settings (e.g. Sport allows it to lock up sooner and in lower gears).

Quote:

I do get a soft "bump" when setting off after having come to a standstill which I put down to a bit of slack in the drivetrain. My (manual) Jeep did the same thing. Slowing down - car is pushing engine, accelerating away - engine pushing car & there's a lot of drivetrain between engine & wheels on a 4x4. Does this sound like the symptom you had & did it go away with TC work?

Yes, much the same. All is now smooth again with a new TC fitted. Pick-up is better, gear changes are better.

In your case, the mileage is a little lower than the point at which TC issues are normally experienced if the fluid is not changed (normally seems to be about 100-120k) but it has been known to happen sooner. It sounds like your vibration may be less severe, which would perhaps concur with the lower mileage.

You might want to try a tube or two of this in the box to see if it relieves the symptoms: http://www.advancedfactors.co.uk/lubeguard...1799-p.asp Many have found it to stop the judder, though it is important to remember that it is not a permanent cure.  Visiting from DISCO3.CO.UK
Discovery 3 TDV6 Auto HSE Zambezi Silver

I'd like to suggest to contact RRPhil, our resident gearbox specialist. He knows a lot about these boxes and may be able to help you on this. Talk to him first before you start doing drastic things  MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!

Is it possible fora single valve to become worn or defective in the valve body which affects the operation of a particular gear? ______________________________
Vogue tdv8 08MY poverty pack - wow