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SMG - noise/clunkiness- normal?

7K views 15 replies 12 participants last post by  CHARIOT 
#1 ·
Apologize if this has been discussed before - did a search and couldn't find much. I'm pretty new to SMG (bought my car 10 days ago). I've been driving manual cars for several years, so I understand the logic behind the gearbox and I have no problem with the way it shifts - quite perfect in fact.

What concerns me a bit (being a gearbox known for having problems) is that it is pretty clunky/noisy, especially when it downshifts. I mean, I can not only feel the clutch when it downshifts, I can also hear it. Not loud, but a clunk/clunk nevertheless. Especially when you let it downshift on its own when coming to a stop.

Is this typical/normal?
 
#2 ·
No, this isn't normal. Assuming there are no errors codes, you can try resetting the adaptations via the paddles, or run a clutch adaptation through INPA. If that doesn't help, you might be due for a new clutch.
 
#3 ·
No codes, I also have re-set the adaptations via shift paddles with no noticeable change in SMG behavior.
I mean, it shifts fine and does everything you ask it, its just not as quiet as I used to on other cars (granted, none were SMG) and since I have no point of reference, I wonder if this is how it supposed to work.
 
#7 · (Edited)
You can definitely feel the downshifts when you let it downshift on its own.

Dealer said that was normal (M Certified Dealer) but I'm not too sure about the noise.

Mine did that occasionally but it wasn't anything that really caught my attention. Clutch and flywheel and smg pressure accumulator were brand new too.
 
#8 ·
What you are explaining is perfectly normal.

I downshift manually at around 3000 rpm when driving normally, until the second gear; and then let it shift into first automatically.

You should never drive in auto mode. It is absolutely horrible.

Also, try to ease up on the throttle as you shift up gears. If you are in S3 or S4, you can also blip the throttle for additional fun.
 
#10 ·
Where would I go to have the Euro SMG flash done? Will BMW dealer be able to do this?
 
#12 · (Edited)
Some clunking is normal by design. (The sh1tty design of the diff, that is.) Wanna silence all drivetrain noise in an ///M car? Ditch the diff...the viscolok design requires slop in the spider gears which in turn translates to slop in driveshaft rotation.

When you're decelerating, the drivetrain goes from being loaded by the engine to being loaded by the weight of the car. In between those points the driveshaft is freewheeling between the toe and heal on the ring gear. (You can confirm this yourself by jacking up the front of your car, rear wheels on the ground, trans in N, then grab the driveshaft; it will spin ~35 degrees each direction. Look down the driveshaft, guess where it's coming from - the diff. The wheels obviously aren't moving since they're planted..) What happens when the clutch grabs while the driveshaft is neither loaded by the motor nor the weight of the car? It slaps clockwise, or counter clockwise depending on which way you're driving. When the driveshaft is cranked in its freewheeling state, the pinion gear smacks either the heel or toe on the ring gear making the dull "thud" everyone explains as the ///M clunk noise from the diff.

Check out my diff thread for more explanation.

From my personal experience, neither the ECE high output tune for DME nor the version 3 euro SMG tune have had any impact on drivetrain noise.
 
#14 ·
I can't agree more with this sentiment. I've always felt the drivetrain slop was the source of a lot of the discomfort. Years ago, (supposedly) BMW passed it off as inherent in the design due to tolerances required for heatup. I doubt if anyone ever actually looked up the coefficient of thermal expansion of the related materials to call BS on that, but that was the word.

IMO, having any variation in the DME's predicted torque and the actual demand torque during a shift will cause an uneven shift that is amplified by the backlash and take-up of the drivetrain.
 
#13 ·
Have the transmission fluid flushed out and replace with new fluid is my recommendation. My M5 has 60k miles, and the car was sluggish in between shifts. After having it flushed out and replaced with new fluid, it shifts so smooth now.
 
#16 ·
The flex disc interfaces the drive shaft to the transmission output shaft. It flexes....but not as much as you would think. Someone needs to come up with a means to modify the factory diff so we have another option compared to spending thousands on a giken unit or equivalent. I took one apart to get to the spider gears but the sneaky germans have beat us to the punch and designed it to not be taken apart. :(
 
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