Sudden jerking in low range

[BSM]

i was up in the Vic High Country on the weekend, when I experienced several sharp jerking movements whilst coasting slowly in low range on a slight downhill gradient. It was like the brakes had suddenly.gripped and then let go. It happened twice along one section and then occurred again about an hour later and about 20 seconds after this later episode a Transmission Fault message appeared on the screen.

It didn't happen again during the trip and didn't happen either during many of the step accents and descents over the weekend. It just occurred these couple of times when coasting in low range slightly downhill.

I pulled out the fault reader a bit later to see if that gave me any clues, but whilst the unit reported a few faults, there were none recorded in the Transmission or Transfer ECU categories.

Any clues about what might be going on here?

[~Rich~]

I have encountered this just about every time off road in hilly country.
The gearbox drops down a gear and you get the sudden take up in the lower gear.
Many other makes get this but on the upshift.
I don't think its a fault, just the way the gearbox works.

[BSM]

I have encountered this just about every time off road in hilly country.
The gearbox drops down a gear and you get the sudden take up in the lower gear.
Many other makes get this but on the upshift.
I don't think its a fault, just the way the gearbox works.

Thanks Rich, I suppose it could be that, very strange though, because it occurs when the transmission is not under much load. I was pretty much coasting, with no pressure applied to the accelerator. Also I didn't get the sense that there was a gear change. I definitely think its something to do with low-range though because It just doesn't happen in High range.

Do you experience this jerkiness on steep slopes, or just on the gentle slope or flat like I experienced it?

[Bytemrk]

What terrain response setting were you in BSM?

Is it possible it was HDC? It can feel like a bit jerking as it cuts in if you are travelling slowly and come off the accelerator.

Down a big steep hill you wouldn't notice the jerk as it would potentially be acting continually

[Celtoid]

What terrain response setting were you in BSM?

Is it possible it was HDC? It can feel like a bit jerking as it cuts in if you are travelling slowly and come off the accelerator.

Down a big steep hill you wouldn't notice the jerk as it would potentially be acting continually

That's what I was thinking. But the Transmission Fault message is interesting. What did it say or was it maybe that HDC had engaged? I'm not familiar with all the messages as I never drive mine through big gradients except on sand so these warnings don't occur.

[BSM]

Thanks for the suggestion. It was definitly not HDC however as I was not using HDC or Terrain response. HDC produces a higher frequency shuddering that I can feel through the wheel. It was not that.

I think Rich might be heading in the right direction, but I'm thinking it was maybe a failed gear change that disengaged from second and then re-engaged greating this jerk as it re-engaged.

I'm going to take it to Ritter.

[Stuart02]

I don't know much about smart gear boxes but perhaps it was the torque converter locking up for a bit of extra engine braking? Shouldn't induce a fault though. Let us know what you find out!

[TD50WA]

Any update on this?

[BSM]

Any update on this?

I had Ritter look into it. They did the scans, and tried to reproduce it, but couldnt. We discussed a couple of theories. But nothing conclusive. Basically its still a mystery.

[TD50WA]

Pity, I have a recon box in mine, some time ago, and was away just recently when found something similar.
In low range and command shift first with no hill descent on, idling in 1st slightly downhill, the car kept grabbing like as if either brakes grabbing - but not abs/hill descent, motor trying to stall, or lockup???
It was a regular action like roll-grab-roll-grab etc etc.

Actually even with normal driving sometimes, when at idle it does the same thing, but infrequently.....

Cheers
Kev