[Harley89]

Originally posted in another thread, but moved it here.

Possible transmission damage during downshift into second


I was driving in town, in sport plus, slowing down to a stop at a red light. I downshifted from 4th to third with no problem, Autoblip did its job. Shifted from 3rd to 2nd and auto blip did nothing but I realized that too late. I experienced a bit of a violent lunge as the car drastically slowed down. There was a decent bang too, but wasn't very loud. As soon as I experienced the jolt, I slammed the pitch back in.

Everything worked fine after ..1-2-3-4 and back down again.

I plan on mentioning this next week when I go in for break in inspection.

Any experience with this or advise would be great, thanks!

[gmzanatta]

Sounds to me like you did not fully engage second gear when downshifting and were perhaps closer to the gate for 4th, which is why the blip wouldn't happen. I've done this downshift many times everyday due to my drive, and have never had any issues.

[Harley89]

Originally Posted by gmzanatta

Sounds to me like you did not fully engage second gear when downshifting and were perhaps closer to the gate for 4th, which is why the blip wouldn't happen. I've done this downshift many times everyday due to my drive, and have never had any issues.

That sounds right, many thanks!

[Jevi Javi]

wow man. Just by reading the title i thought for a sec there could be a new recall coming...

[M3 Adjuster]

Originally Posted by Jevi Javi

wow man. Just by reading the title i thought for a sec there could be a new recall coming...

I'm still trying to figure this out.

Is the OP a driver that is so new to manual transmissions that he isn't sure what actual engine braking is and was confused by the laws of physics?

Heaven help those that only know automatics (yes that includes DCT- which are a type of automatic )

[Harley89]

Originally Posted by M3 Adjuster

I'm still trying to figure this out.

Is the OP a driver that is so new to manual transmissions that he isn't sure what actual engine braking is and was confused by the laws of physics?

Heaven help those that only know automatics (yes that includes DCT- which are a type of automatic )

I've been driving a manual for 5 years now, As I said it was a violent jolt. Proper engine breaking isn't violent... at least mine isn't.
Thanks for assuming the best scenario though ?

[chris719]

I thought it was pretty clear. He expected the rev match feature to work, so he abruptly let the clutch out assuming a perfect match and instead got a violent reaction from the drivetrain as you would expect if you dump the clutch without matching revs.

The question is why exactly did the rev match feature not work. The sensors should trigger before it even enters the gear. Were you perhaps too slow or too deliberate? It might have a time limit? (I don't own an M2)

[Harley89]

Originally Posted by chris719

I thought it was pretty clear. He expected the rev match feature to work, so he abruptly let the clutch out assuming a perfect match and instead got a violent reaction from the drivetrain as you would expect if you dump the clutch without matching revs.

The question is why exactly did the rev match feature not work. The sensors should trigger before it even enters the gear. Were you perhaps too slow or too deliberate? It might have a time limit? (I don't own an M2)

Thanks. There hasn't been any other mention of the issue with any other vehicles. So probably safe to assume operator error. Wasn't shifting fast at that point, and dropped the clutch fairly quick, so I probably tripped up the computer.

[M3 Adjuster]

Originally Posted by chris719

I thought it was pretty clear. He expected the rev match feature to work, so he abruptly let the clutch out assuming a perfect match and instead got a violent reaction from the drivetrain as you would expect if you dump the clutch without matching revs.

The question is why exactly did the rev match feature not work. The sensors should trigger before it even enters the gear. Were you perhaps too slow or too deliberate? It might have a time limit? (I don't own an M2)

So in other words , it was engine braking ...

[M3 Adjuster]

Originally Posted by Harley89

I've been driving a manual for 5 years now, As I said it was a violent jolt. Proper engine breaking isn't violent... at least mine isn't.
Thanks for assuming the best scenario though ?

Proper engine *breaking* is often times but not always violent.

(Im)Proper engine braking also can be violent, particularly if you drop the car into gear without using the clutch... . It's very possible the bang was the engine bouncing off the rev limiter. That or normal M2 backfire downshifting burbling at higher than normal rpm.

Good to hear that the car seems to be no worse for the wear.

[chris719]

Originally Posted by M3 Adjuster

So in other words , it was engine braking ...

He's asking why the auto rev match didn't work. I don't see why this is hard to understand?

[Harley89]

Originally Posted by M3 Adjuster

Proper engine *breaking* is often times but not always violent.

(Im)Proper engine braking also can be violent, particularly if you drop the car into gear without using the clutch... . It's very possible the bang was the engine bouncing off the rev limiter. That or normal M2 backfire downshifting burbling at higher than normal rpm.

Good to hear that the car seems to be no worse for the wear.

Grammatical error without rebuttal, I was on "break" when I wrote it so Freudian slip? Not much I can say about that

It definitely was not any back fire or the like, It was a slam. No pop, no crackle. It's been driving fine since, so I'm not overly concerned. It's just the first issue I've had with it (issue likely being my fault). I just thought checking here to see if anyone else had the same issue occur, should be my first step in diagnosis.