C5 X7 Manual gear problem

[mypinknee]

Can anybody explain what is happening? I am driving along and go to change up a gear but instead of going from 4th to 5th it jumps to a lower gear.
The change down is violent but there is no crunching or anything. It is as though I had chosen the wrong gear, but I had no choice in the matter.
This only happened 2 or 3 times yesterday, and I didn't have time to make all the observations and analysis I would like to have done. Especially as this problem occurred in a busy traffic situation causing people following me extreme alarm, as presumably no brake light was visible to them when I slowed down so fast.
All clues as to what to look for will be welcome.

[GiveMeABreak]

Please pop your VIN here so I can check the exact box you have and for any applicable any TSBs.

[Paul-R]

I'm unclear whether this is a manual gearbox or an auto gearbox used in manual mode.

[mypinknee]

The box is manual.

[mypinknee]

Please pop your VIN here so I can check the exact box you have and for any applicable any TSBs.

VF7**************[VIN obfuscated, can be read by forum staff]

[Paul-R]

So it sounds like when you're going over from the 3rd/4th plane to the 5th/6th plane it's actually staying in the 3rd/4th plane and you then select 3rd instead of 5th.

Does it feel as though you're going into the 5th/6th plane, i.e. is there some resistance, or is it just a "looseness" moving over?

[paulmac1978]

I’ve had a similar issue on a C5 X7, it was the ball joints where the gearbox cables join the gear linkage. They needed cleaned and greased. One was seizing/sticking so the wrong gear was being selected.

[mypinknee]

So it sounds like when you're going over from the 3rd/4th plane to the 5th/6th plane it's actually staying in the 3rd/4th plane and you then select 3rd instead of 5th.

Does it feel as though you're going into the 5th/6th plane, i.e. is there some resistance, or is it just a "looseness" moving over?

There was no resistance at all and it frightened me nearly to death!
It only happened three times on my way out. The return journey was fine and the fault did not reoccur.

[GiveMeABreak]

So 6 speed (ML6C) fitted on this model.

Possible symptoms:

• Impossible to engage gears
• Changing gear difficult
• The gear engaged is not one wanted
• No drive of the vehicle
• Clutch release difficult or impossible
• The clutch pedal remains on the floor(Permanently or intermittently)
• The clutch pedal is hard or soft
• The clutch pedal does not rise completely or does so in 2 stages
• Brake fluid leak (Clutch control)
• Oil leak from the gearbox

There are multiple checks required to determine the cause, from faulty gear cables, hydraulic control slave cylinder, clutch etc., many of the checks involve measurements and another person, so probably left to the garage to diagnose.

There is a check you can do:

• Engine stopped: Declutch and keep the clutch pedal pressed down during the operation
• Carry out one of the difficult gear engagements (whichever one you had the problem with - i.e. 4th to 5th)
• Stay declutched
• Move the gear lever to the neutral position
• Carry out the same gear engagement (whichever one you had the problem with - i.e. 4th to 5th)

Following the above, is it difficult to engage the same gear the second time? If the answer is 'yes', then the gear shift control cables need to be checked / adjusted / replaced.

[mypinknee]

Yes - 6 speed. Thanks. I will try out your last suggestion.
I am sure it is well beyond me to fix, but as ever I appreciate your advice.
My only comment is it is not difficult to change gear in any way.

[mypinknee]

Yes - 6 speed. Thanks. I will try out your last suggestion.
I am sure it is well beyond me to fix, but as ever I appreciate your advice.
My only comment is it is not difficult to change gear in any way.

Just tried the de-clutch test and there was no problem.

[GiveMeABreak]

Ok so if there is no problem with that test, then you are into the realms of checking the travel of the hydraulic clutch control slave cylinder, synchromesh and other tests involving the clutch and flywheel. So see how it goes and if you get persistent issues, keep a record of the issues (which gears are difficult to engage, any issues selecting reverse, does it jump out of gear, etc,) so you can provide as much detail to any garage / dealer if necessary.