Auto gearbox issue.

[Border]

Hello everyone. I have a 2018 C220d estate with the 9speed auto box with 29k miles. Serviced by MB at year 1 and 2 and recently serviced and MOT by independent MB specialist as it is now just 3 yrs old.
I have had an intermittent issue for approx 18 months.
Occasionally when selecting D or R from park the gear goes in with a definite clunk. There seems to be no pattern as to when ie hot or cold etc . Also when slowing down say when approaching a junction etc at around 10 to 15 mph as the box changes down it sometimes does down change again with a real jerk and clunk. This only happens very occasionally. I have had the car into MB a few times. They tell me there are no error codes or faults stored. They have downloaded the latest software etc and the last time
( 6 weeks ago ) kept the car for a few days and said they had recoded each gear at cold , medium and hot temperatures ? They have not been able to recreate the issue on road tests. The box does seem smoother in general since then but has still had the clunks as described around 4 times since. I asked about a gearbox service but was told it was a service thing and they would not do it under warranty. If I wanted to pay the £470 to have it done early they would.
Is it worth having the gearbox service done ?
I would appreciate any thoughts or advice. Many thanks in advance.

 

[Jim2]

At the very least I'd be getting the ATF level checked , and see what the fluid looks like by someone who knows what he's doing.

 

[LostKiwi]

When it clunks are you on a hill or incline?

 

[Wighty]

As above , could it be a combination of parking brake releasing combined with putting it into gear (when it isn’t on the flat )

 

[Jim2]

Clunking when on a slope would indicate a low ATF level. And a very low level at that.

 

[Border]

Thanks. No the clunk when selecting D or R is on the flat. I presume the independent specialist where it was recently serviced can check the transmission fluid level ? Is that a simple job ?

 

[AnthonyUK]

Thanks. No the clunk when selecting D or R is on the flat. I presume the independent specialist where it was recently serviced can check the transmission fluid level ? Is that a simple job ?

Yeah. It has a dipstick tube and most garages will have a suitable dipstick.

 

[Border]

Many thanks.

 

[Manc Rick]

I don’t suggest this is your problem, but what is your routine when parking up? i notice some people stop and put the box into park, then apply the handbrake, which is putting the weight of the car on the parking pawl (even more so if on an incline). When this happens, this can cause a jerk when moving from park to drive / reverse.

Happened to me when I first got an auto. Since then, I always let the car rest, apply the handbrake with the box in neutral, then I put it into park.

 

[Border]

Thanks for that. I must confess I usually put the car in Park and the auto handbrake sets itself . I will try your suggestion.

 

[Jim2]

Thanks. No the clunk when selecting D or R is on the flat. I presume the independent specialist where it was recently serviced can check the transmission fluid level ? Is that a simple job ?

As yours is the 9 speed, transmission, not so simple as it does not have a dipstick ( you only find dipsticks on the 5 speed 722.6 transmissions, and even at that they are not standard issue, like the engine oil dipstick ) For your 9 speed, the car has to be sitting level on a lift, then with the engine running, hand brake on and selector in "P", with the ATF at exactly 45c ,you loosen the trans sump drain plug, and see if any fluid comes out, if not, then the level is too low. If a small amount trickles out, its fine....replace the sump plug immediately.
Now for the tricky bit.....if its reading low, and needs a top up, you will need:
Threaded adaptor to screw into the sump stud opening.
On/ off tap to fit on the adapter pipe.
Hand Pump ( 5 ltr capacity will do)
4/5 Ltrs of the correct ATF for your vehicle ( very important,,dont mix ATF. Consult MB Bevo list to identify correct fluid for your car}
Fill pump and connect it to the adaptor ( which will have the open / shut tap already on the pipe)
Set the tap to "Open" and Pump one ltr of the new fluid into the transmission, switch off the tap. Allow a few moments for it to settle, then open the tap fully, and see if any fluid comes out, If not, pump in some more, and again close the tap, Repeat this procedure until fluid starts to flow back out, When this happens, allow it to flow until it stops or slows down to a few drops. When this happens, close the tap, remove the adapter and replace it with the sump plug. Job Done....

 

[Border]

Thanks for that very detailed information Jim !
I think that is why forums like this are a great place for help and assistance and detailed know how.
However for me and my abilities I think a trip to the independent garage who recently serviced it beckons ! and have a word and do the checks and if needs be I will get them to do fluid change and gearbox service.
Many thanks again.

 

[Jim2]

Thanks for that very detailed information Jim !
I think that is why forums like this are a great place for help and assistance and detailed know how.
However for me and my abilities I think a trip to the independent garage who recently serviced it beckons ! and have a word and do the checks and if needs be I will get them to do fluid change and gearbox service.
Many thanks again.

Yes, most people think when you mention " check the oil level" , its associated with checking the engine oil level. A far less complicated job that checking the ATF in an automatic box. Better safe than sorry, you are right to take it to a professional. Let us know how you get on, OK?

 

[Botus]

Occasionally when selecting D or R from park the gear goes in with a definite clunk. There seems to be no pattern as to when ie hot or cold etc .

when you park on inclines are you using the park brake first, or just selecting P ?

its really bad behaviour to park ANY automatic on any form of incline only using P - its also dangerous and illegal on a public road

on the flat its quite acceptable (but still illegal), P is only a basic bodge for additional protection in-case you forget the park/hand brake - it is a rudimentary "jam a spanner in the works" ideal and on many Autos a very fragile way to hold a car still. It can slip out - hence why its illegal to only use this method. The Merc parking pawl is more robust than most, but its still abuse and the massive clonk you randomly hear and feel may be the very powerful mechanism trying to un-jam that "spanner". When used on a hill it is possible to jam in with such force its can be impossible to get it out again - we often had cars towed in (not on Mercs) where ignorant owners had got stuck and it was a gearbox out job to fix the damage

Also when slowing down say when approaching a junction etc at around 10 to 15 mph as the box changes down it sometimes does down change again with a real jerk and clunk. This only happens very occasionally. I have had the car into MB a few times.

get the fluid changed and have the gearbox adaptions reset and see if it gets over itself - someone like Alex at AMF will be able to check what the current solenoid fill rates are doing and let you know if its wearing itself out

Try not to go to a main dealer they are robbing idiots without a clue, usually crewed by sacked McDonalds workers who's experience of cars comes from a PS5

 

[Border]

Thanks for your reply Botus. When you think logically about it it makes perfect sense what you say. I do park on the flat but will certainly make a point of making sure the handbrake is applied correctly. I agree with you about large main dealerships. Like most people I don't mind paying for something doing but it is having the confidence and trust that that whatever it is has been done properly. Cheers.

 

[Jim2]

when you park on inclines are you using the park brake first, or just selecting P ?

its really bad behaviour to park ANY automatic on any form of incline only using P - its also dangerous and illegal on a public road

on the flat its quite acceptable (but still illegal), P is only a basic bodge for additional protection in-case you forget the park/hand brake - it is a rudimentary "jam a spanner in the works" ideal and on many Autos a very fragile way to hold a car still. It can slip out - hence why its illegal to only use this method. The Merc parking pawl is more robust than most, but its still abuse and the massive clonk you randomly hear and feel may be the very powerful mechanism trying to un-jam that "spanner". When used on a hill it is possible to jam in with such force its can be impossible to get it out again - we often had cars towed in (not on Mercs) where ignorant owners had got stuck and it was a gearbox out job to fix the damage


get the fluid changed and have the gearbox adaptions reset and see if it gets over itself - someone like Alex at AMF will be able to check what the current solenoid fill rates are doing and let you know if its wearing itself out

Try not to go to a main dealer they are robbing idiots without a clue, usually crewed by sacked McDonalds workers who's experience of cars comes from a PS5

When parking, my SOP is:- Foot on brake, ( firmly), switch transmission to "P", then hand/foot brake fully on, switch off engine. Job done. If you have driven HGV's, its second nature.