I was driving home from IKEA late at night in Muscat, Oman

Possibly the only reason I agreed to do this was to drive the XKR.
There is a section of road that is a single lane with a central reservation that winds up over a bridge that is being fixed.. it feels like a hill climb track

I wanted to raise my pulse a bit, so I was in manual mode and 2nd gear (traction off) going around the hairpin part, then I stepped on the power coming out and going up the hill.
The rear didn't slip on the sandy road as much as expected, and there was quite a loud "BANG" or loud clunking sound a second or so after I stepped on the power, I was a bit confused as I knew I hadn't hit anything (sounded like I hit the kerb), but I carried on.

When I was nearer home I wanted to try accelerating hard again to see if this is what caused the sound..
So slowed down, dropped it to 2nd in manual and accelerated hard (foot to the floor).

The car got to around 4k revs (maybe more) and then "BANG" (loud clunk) and the transmission changed to auto mode.
I did it once more to confirm, and the next time it almost seemed like the car carried on accelerating after the bang / changing to manual, and I had to brake to slow it (this might be my imagination, but it felt strange). I think the last time I tried it in 3rd (same result).

I'm guessing this is the gearbox?

I came home and checked the codes - no faults stored.
Not sure what to look for in live/diagnostic data.

Worst part is I was returning a load of stuff my wife bought in the IKEA sale, after she decided we don;t need it.. so the whole journey was also a waste of time!

I am presuming my car never had an gearbox oil change - the previous owner sold it to me with bad engine mounts and all suspension rubber cracked/perished (Oman heat).

thanks to anyone who can advise.
Steve.

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XKR 2009 4.2 - no service history.. the previous owner says it was serviced at Bentley (I think it was just never serviced).

 

It does sound as if the gearbox might be at fault but what you are doing should not cause a problem unless the problem already exists. How many miles has the car done? If it's more than 100k and the fluid has never been changed then it could well be the auto box. However, it could also be engine mounts, universal joints or a diff problem although the fact that it changed itself from manual to auto does suggest a gearbox issue. However, if you rev the engine too much in manual then it might well change to auto so that might be a possibility.

I would have all these things checked and, if more than 75k, have the auto and diff fluid changed before assuming the worst.

Richard

 

I'm sort of on the side of the rear diff did a bad thing. Also what Richard said; change every fluid possible.

 

You mentioned "perished" rubber components; did you take a look at the driveshaft coupler

 

Also transmission mount.

 

Start with a visual inspection and look for loose and worn driveline components. As mentioned replace the transmission pan, fluid and mechatronic sleeve.

 

I drove it today.. more gently and thought it was okay.
Unfortunately when I put more load on it I get the same thing.


Video below of the dash - you can hear the engine rev suddenly then it 'bangs' at the end.
What can't be seen in the video is that the display shows the gearbox swapped back to AUTO at the same time as the revs suddenly increase (like that car made a shift.. but it feels like it went into neutral).

The car was in 2nd gear.. so I should be able to keep it in 2nd in manual all the way to the redline if all is working correctly? No reason for it it change gears?

Obviously, I don't want to drive it like this - but I am curious if it is changing down to 1st gear. I did have my diagnostic tool connected when I took the video but it only records snapshots.. not continuous data.. the data says it was in 2nd gear on both data snap shots it took - on the live data I would have been able to see if it changed.. but I couldn't look at the screen while driving / filming.

One strange thing I just noticed is that the speedo also jumped from 50 to 70.. the car definitely didn't speed up.. it slowed down.
Wondering if its changing to 1st.. and what the bang is.. really sounds like the gearbox reengaging after slipping - but no idea why it would slip and then reengage so violently if that is the case?

 

I went to the Jag dealer in Muscat to get a price for oil change. They quoted for oil / filter and labour.. 390 OMR.
In real money that is Ł‎828 or $1012!

They did say I could bring my own oil / parts.. and that they would just rip me off for the labour $363 / Ł‎297,
No mention of 'Mechatronic sleave' tho.

Wondering if I can easily check the level first?

 

I've already replace the engine ./ transmission mounts.
the 3x mounts in the image were changed.. is there another one?

 

When you say you were in manual mode -- did you have the shifter in "S" or were you in "D" taking manual control with the paddles?

 

It was in 'D' and I shifted it to 2nd then accelerated.

 

You can check the level if you can raise the car off the ground and lie under it with the engine running but, even then, it is not easy as you'll be working in a confined space right alongside the hot exhaust.

How many miles has the car done?

The video does look to me as if the clutches in the autobox are slipping and then grabbing which could be symptom of old fluid and worn internals. The mileage that the car has done would assist in determining this possibility.

Richard

 

I think Richard is right. It may also be related to the autoshift feature kicking in early.

 

Order it all online, any competent transmission service shop can do it for you. Mechatronic sleeve has the chance it will leak and this can cause odd electrical things, so change it while its open