XSeries-forum

My initial 1 year warranty after purchasing from a main dealer has about a month to go and though I will probably renew I am aware that the original one is more comprehensive so want to check all is ok now.

Regarding the auto gearbox, is it normal that when you put your foot down to go (fairly hard but not necessarily flooring it) then back off a bit for whatever reason, then put your foot down again that there is a nasty drivetrain shunt, the kind that feels (and possibly sounds) 'painful'. Everything works fine, it's just horrible when it happens and the more you are pressing the accelerator at the time the worse it is. To add to the explanation, say you were pulling out or accelerating then saw something that made you hesitate or just lift off, then find it's ok to go so press the accelerator again within a short space of time - that's when it happens.

This may be normal but I'm new to automatics and to 4x4 so have no idea. It's not something I'd want to demonstrate to someone really either as I try to avoid it situations where it can happen but sometimes it can't be avoided (heavy traffic, stop start etc).

Whilst I'm at it, is there anything else I should check before the warranty expires that is easy to check myself?

Thanks

Sounds like the 'lurch' to me , try a reset with the throttle, or needs a software update.
Plenty of info on this site, search 'Lurch'
Lez

Ok, thanks, I did do a reset a while back but don't know if the software is up to date. Do the main dealers check software is up to date as a matter of routine?

I've just scan read some of the links and it does seem like it is along the same lines. It's very low mileage (just over 20,000) and is generally fine so hopefully it's just the software update. I'll ask the dealer and will be renewing my warranty in any case.

I must admit not having heard / seen about the lurch when accelerating, more when slowing down coming to a stop.

It's pretty easy to avoid it and it's only happened maybe three times so probably isn't an issue as such but I'll mention 'the lurch' to the dealer and that I've heard software updates can help and see what they say. I just hope they don't try and charge me!

My E53 did it a few times and I agree that it can make you cringe. I think mine only did it maybe two or three times in all the time I owned it, and I learned not to do a go-lift off-go so that I avoided it. I always thought it was caused by the tranmission loading up to accelerate, then changing to the braking cycle as the throttle was chopped, followed by a sudden throttle increase causing the system to get caught partway between the drive type change (power to brake and back to power in quick succession) and the 'slack' in the driveline resulting in a transmission 'snatch' as the power came back on.

I'm not talking about power and brake in terms of driver actions, but within the gearbox itself where there will be loads being transferred via the power and brake clutches. As the various clutches have a defined changeover cycle timeline using overlapped controls managed by the Mechatronics Module, I think it's possible that the clutches can be caught out momentarily if the power on-off-on input arrives at the critical point where no single brake or power clutch is fully engaged so the box is almost starting to freewheel before getting loaded up again and hence the 'clang' as the system sorts itself out.

At least that's my theory on it anyway