Auto clunk...

[Bing]

It seems to be Clunk Month, so I thought I'd add a new one

This is a different one though... I have an auto, and maybe 1 in 5 times when I stop and shift from drive to park I get a meaty clunk from the rear and the car moves just a little. Doesn't happen every time, and it makes no difference whether the car is level or on a slope. Anyone got any ideas ?

Possibly related, when driving and under moderate acceleration, occassionally as the box shifts from 2nd to 3rd there is a slight pause and then small jerk into gear. Doesn't happen when I am using the paddles. I know nothing about gear boxes, but a customer who does said it may need the ECU tweaked by a dealer to sort the gear ratios. Or something like that :?

Are the two related or do I have two different problems, and can anyone help with either ? Doesn't seem terminal, but is just a nagging worry. Cheers !

 

[thefmister]

Do you feel a similar clunk when you brake and the box goes to first gear i.e. to stop for a red light? I had this on my previous Citroen with ZF box. Tried flashing the software and had the oil replaced although it's sealed for life. Didn't really helped. But they did say that the oil comming out was clean so no excessive wear on the inner parts.

 

[pvr]

On the X5, there is a "soft reset" option which may cure it, but don't know if the same applies to a Z:

1. Ignition to position 2 (just before startup)
2. Push the accelerator pedal all the way down and count to 30-40 seconds
3. Put your foot on the brake now
4. Start the car and drive FORWARD

 

[Bing]

thefmister, no - the car doesn't go into first gear when you stop at lights, goes to second. Which is a bit weird, but doesn't affect performance when driving in full auto. It'll only go to 1st if I paddle it down. And there's no clunk. When stopped and going into park it is almost like the disengage of the gearbox is a bit too harsh.

pvr, thanks - I'll give this a try when I go out later and report back

 

[thefmister]

thefmister, no - the car doesn't go into first gear when you stop at lights, goes to second. Which is a bit weird, but doesn't affect performance when driving in full auto. It'll only go to 1st if I paddle it down. And there's no clunk. When stopped and going into park it is almost like the disengage of the gearbox is a bit too harsh.

pvr, thanks - I'll give this a try when I go out later and report back

Thats also something I had. I had a 3l V6 in the Citroen so for driving off in second wasn't a problem but not how its supposed to be. When I set it to manual and shift down to 1st it would do this without clunk, but when left in auto it would.

 

[Blue]

The E39 Auto is supposed to pull away in second gear, it only uses 1st if you engage Sport mode or it's on a steep hill etc.

Is the clunk not just the diff at the back of the car? As Drive is engaged the energy should travel into the diff which may allow a tiny little bit of movement before clunking to a stop.

I bet it's related to the way the diff clunks in the manual Z4s when manouvering.

As the noise is coming from the rear of the car I think it's safe to assume that it's nothing to do with the box, thankfully

 

[Bing]

:slaphead: of course, the gearbox is not at the back. So must be the diff disengaging ? I will look on the other threads about manuals... But for my thread - is it bad ?

 

[john56]

Bing, if you lift your foot off the throttle just a s the box changes up you will get a kick or clunk from the the gearbox, its just taking up the slack in the transmission, it should change smoothly without any clunks if you are accelerating as all the slack in the transmission is taken up, i have two cars with auto and they both do this, it should be more of a kick than a clunk though.
The clunk you are getting when you move out of drive into park is a bit of a mystery, you have to move through neutral first, does it clunk when you move out of drive into neutral?

 

[Bing]

Bing, if you lift your foot off the throttle just a s the box changes up you will get a kick or clunk from the the gearbox, its just taking up the slack in the transmission, it should change smoothly without any clunks if you are accelerating as all the slack in the transmission is taken up, i have two cars with auto and they both do this, it should be more of a kick than a clunk though.
The clunk you are getting when you move out of drive into park is a bit of a mystery, you have to move through neutral first, does it clunk when you move out of drive into neutral?

Thanks John - I did PVR's soft reset and actually it seemed to work on the in-motion jerk. Changes are a lot smoother than they were before and there is no jerk. It could be my imagination but the throttle seems a little sharper too.

As for the rear clink, don't know as I haven't tried - normally go straight through neutral to park. At loghts if i move into neutral the only motion is the rear rising slightly as the drive chain is disengaged, and it then sinks again when I go back to drive. I shall try the drive-neutral and pause-park tomorrow

 

[bcworkz]

As with manuals, try checking the guibo disc.