DCT 3rd —> 4th Gear Change in D1 *Thwack* Noise

[mfurse]

Hey everyone, first thread! I'm loving my 2016 LCI M3 and have been DDing it for a few weeks now.

One thing I can't work if it's normal or not is regardless if warm or cold I hear a subtle thump/thwack noise from the rear when the car goes from 3rd to 4th in D1 at gentle load (so slightly accelerating from 40 kmph to 50 kmph when it shifts up itself). I can also get similar when it's cold and in M2 also at slightly more revs.

There's no vibration, no shunt - just a noise like someone whacking an upturned plastic bin with an open hand! (Best description I can give haha).

No noise between other gears or at other speeds. Was thinking of getting diff and gearbox fluids changed prematurely as the cars only done 17K KMs, see if that calms things down.

(Also, I've owned a 1M and an e90 M3 with DCT so I know how these DCT boxes are not the most "refined").

Anyone with similar behaviour? Will also get dealer to check it out.

[Sinnakle]

Originally Posted by mfurse

Hey everyone, first thread! I'm loving my 2016 LCI M3 and have been DDing it for a few weeks now.

One thing I can't work if it's normal or not is regardless if warm or cold I hear a subtle thump/thwack noise from the rear when the car goes from 3rd to 4th in D1 at gentle load (so slightly accelerating from 40 kmph to 50 kmph when it shifts up itself). I can also get similar when it's cold and in M2 also at slightly more revs.

There's no vibration, no shunt - just a noise like someone whacking an upturned plastic bin with an open hand! (Best description I can give haha).

No noise between other gears or at other speeds. Was thinking of getting diff and gearbox fluids changed prematurely as the cars only done 17K KMs, see if that calms things down.

(Also, I've owned a 1M and an e90 M3 with DCT so I know how these DCT boxes are not the most "refined").

Anyone with similar behaviour? Will also get dealer to check it out.

Take it into BMW and tell them about the noise. They will probably give you a new transmission it'll take like 3-4 days.

[mfurse]

Going in this week for checking by the dealer - hopefully nothing too bad.

[mfurse]

Originally Posted by mfurse

Going in this week for checking by the dealer - hopefully nothing too bad.

Went into dealer this morning - helpful tech went for a drive with me riding shotgun. He could make it do the noise everytime in M2 and even when he knocked it into neutral. They had the car all day inspecting it and have raised a technical advisory with BMW for their view. They said it's not dangerous as far as they are concerned locally but the noise isn't normal.

[Yachtmaster]

Sound similar?

[mfurse]

- here's a 2nd > 3rd shift with the thwack noise from the rear.

[mfurse]

Transpires it's likely a failing synchro gear so new DCT box has been ordered. Great service so far though - can't fault the dealer for promptness, communication and service.

[waterbottle1]

My mate had this exact on a higher km M4 and exactly in 3rd to 4th mid 40kmh
He got it flushed out. Tranny service.
Issue gone after.

[mfurse]

Originally Posted by waterbottle1

My mate had this exact on a higher km M4 and exactly in 3rd to 4th mid 40kmh
He got it flushed out. Tranny service.
Issue gone after.

Good to know - I think "life time" fill isn't really right on the fluids in these boxes. I'll be doing mine at 50k. Mine definitely had a worn synchro though as it had only covered 15000KMs.

[Perrym3mmm]

Originally Posted by mfurse

Transpires it's likely a failing synchro gear so new DCT box has been ordered. Great service so far though - can't fault the dealer for promptness, communication and service.

I hope the new DCT box has been running fine since then. Do you mind sharing if BMW charged you for the new DCT box ?

[M3SQRD]

Glad to hear BMW is replacing your DCT

[mfurse]

Originally Posted by Perrym3mmm

I hope the new DCT box has been running fine since then. Do you mind sharing if BMW charged you for the new DCT box ?

Nothing, was all warranty. Took a while to get shipped from Germany and lots of seals, oil, bolts and mounts added to. $42K AUD job if I had to pay myself, lucky was all warrantied and had a loaner car too.