2016 W212 350d gearbox noise. 96k miles. Full MB SH.

[Kirkmeister]

Hi, I've posted before about an unusual noise from my gearbox when in D1 or R.
When selecting either of those after P, I get a creaking type sound from the front right of the car. This only happens though when the car has been running for an hour or so. If you roll to a stop to D1, there's no odd noise. It only comes on after you move back into N, then into D.
My Mercedes dealer is unsure about this, though they have witnessed the sound.
My neighbour, a retired Range Rover technician, suggests is an internal valve or pump in the auto box.
Has anyone experienced a similar issue? Are there such valves in the auto box?

 

[Tonygw]

Are 100% sure its from the gearbox?

 

[KennyN]

Front right of the vehicle is nowhere near the gearbox / drivetrain unless it is 4 matic ?

Are you sure its not creaking through the brakes whilst holding against the gearbox ?

K

 

[Kirkmeister]

Pretty sure. Its only audible when you shift from N to D or R. If you hold it on the brakes it happens, and continues when you release them. It seem to stop at speeds greater than 10mph (or perhaps other noises drown it out)
It only starts after the cars been running for around an hour, and only ever after you've engaged N. If you coast to a stop, leave it in D (eg traffic light) and start straight off it doesn't happen.
one witness describes the sound like I have a frog in the engine bay...croaks every few seconds. Doesn't seem to be suspension or power steering as it occurs when not moving.

 

[Kirkmeister]

Front right of the vehicle is nowhere near the gearbox / drivetrain unless it is 4 matic ?

Are you sure its not creaking through the brakes whilst holding against the gearbox ?

K

Thanks...it occurs when moving away in D1 with no braking. I wish it was the brakes...less formidable than a gearbox issue

 

[KennyN]

What happens if you pull away from standstill with the car in D2 ?

K

 

[Kirkmeister]

What happens if you pull away from standstill with the car in D2 ?

K

I've not tried that. Good idea..next time its up to temp I'll give it a go.

 

[Bellow]

I get a creaking type sound from the front right of the car.

Is that where the trans cooler is located?

 

[Kirkmeister]

Is that where the trans cooler is located?

Thanks Bellow, I assume that's the transmission cooler? I've no idea where it would be but could be an interesting option to consider as the noise only develops after the car has run for about an hour.

 

[Bellow]

Thanks Bellow, I assume that's the transmission cooler? I've no idea where it would be but could be an interesting option to consider as the noise only develops after the car has run for about an hour.

Yep, the transmission cooler - which will be a 'saddle' cooler ie, as a part of the main engine cooling radiator. It may or may not have a thermostat within the system - I don't know enough about your car/model to know.
What I'm wondering is if there is some problem there or, if your oil level is a touch low. Generally speaking, the ATF flows to the cooler from the torque convertor (which is its greatest inputter of heat) to the cooler. When an instruction is given for the gearbox to do something - eg, go from N to D, oil is drawn from the pressure circuit (from which the torque convertor is fed) to enable gear selection. Were this to impair the flow to the cooler, it may cause a pressure drop (or complete starvation) which may manifest as noise in the external plumbing to and from or within the cooler.
Note, the above is a generalisation and your transmission could be configured differently nonetheless, I'd check its fluid level first, Maybe homing on on the cooler and listening there may offer up more clues. When checking the fluid level, look for excessive foaming of the oil also. Air entrainment could cause noise and would be because air was entering the suction pipe between the contents of the oil pan and the pump. Unlikely as it would likely impede on torque convertor operation but not impossible (and possibly overlooked if most torque convertor operation is with its clutch locked) but if so, needs to be remedied reasonably quickly (a job any competent garage could do).

 

[Kirkmeister]

Thanks Bellow for this in depth overview. A lot of what your suggesting to check is above my technical knowledge but it does give me some direction to share with my garage as a possible cause.
I can suggest this for them to inspect, so they are then somewhat obliged to do so. I'm very comfortable with my 350d 212 and will pay to keep it at top condition, though issues with the gearbox concern me as many garages seem reluctant to take on the challenge.
I appreciate you taking the time to share.

 

[Kirkmeister]

Hi there,
An update from my original enquiry. It been suggested that this noise is originating from the 'eco boost pump' rather than the gearbox.
As the gearbox seems to be faultless, and the noise only occurs when at rest or just starting off this seems to make some sort of sense.
Would anyone have any thoughts on this? Does it sound feasible?