Sometimes engine revs unclutched during M-mode shifting?

BMW135pls · 06-12-2015, 08:15 PM

Recently I've noticed while driving in M-Mode, that occasionally when shifting, the gear will declutch, but the throttle is still being sent to the engine for a split second. What you get is an occasional rev that goes a few hundred RPMs higher than where you were at when you clicked the shift button. Similar to if you tried to shift a MT without releasing the throttle during shifting.

Is this a common issue? Harmless software glitch, or indicative of potential upcoming hardware issues?

Cavpilot2k · 06-13-2015, 12:00 AM

Hmmm. You know, I've never had that problem, but then again, if you clutch has no software, your clutch won't do funny software stuff...

saace7 · 06-13-2015, 10:45 AM

OP has an AT but i see what you did there

Is the slipping during WOT pulls/hard driving or during regular driving or both?

BMW135pls · 06-13-2015, 10:58 AM

Quote:

Originally Posted by saace7

OP has an AT but i see what you did there

Is the slipping during WOT pulls/hard driving or during regular driving or both?

I've seen it happen in both situations, but it's not terribly common either way.

Solo_M_Tech · 06-13-2015, 04:30 PM

Torque converter/ transmission slip. Fluid/filter change may be needed. Each gear's clutch pack is slipping when engaged.

BMW135pls · 06-13-2015, 05:21 PM

Quote:

Originally Posted by ApexResistance

Torque converter/ transmission slip. Fluid/filter change may be needed. Each gear's clutch pack is slipping when engaged.

Hmm... I just had a trans flush and filter replacement a few months ago when the trans gasket started to leak. At 58k miles it seems a little early to suspect the Trans itself starting to go. Maybe the fluid wasn't the best kind to use?

Andrewcoja · 06-13-2015, 09:13 PM

AT doesn't have a clutch, it has a torque converter.

Solo_M_Tech · 06-14-2015, 05:44 AM

Quote:

Originally Posted by Andrewcoja

AT doesn't have a clutch, it has a torque converter.

Do you know how an automatic transmission works? Each gear has a wet clutch pack, made up of "steels" and friction discs. The more steels and friction discs, the quicker the shift, and more torque holding capability. When the friction discs get worn out, or the fluid is too low, they can slip, overheat, and burn up. Typically noticed first when the transmission is trying to change gears. The friction discs and steels will slip when torque is applied, until they catch. That momentary slip is noticed as a short blip in the rpms during gear change. I'm not saying the transmission is failing, but if the
Fluid is low, too hot, or the wrong type, it can cause these gear packs to slip.

06-12-2015, 08:15 PM	#1
BMW135pls First Lieutenant 90 Rep 341 Posts Drives: Bucket of screws and sadness Join Date: Jul 2014 Location: NJ, USA iTrader: (0)	Sometimes engine revs unclutched during M-mode shifting? Recently I've noticed while driving in M-Mode, that occasionally when shifting, the gear will declutch, but the throttle is still being sent to the engine for a split second. What you get is an occasional rev that goes a few hundred RPMs higher than where you were at when you clicked the shift button. Similar to if you tried to shift a MT without releasing the throttle during shifting. Is this a common issue? Harmless software glitch, or indicative of potential upcoming hardware issues? __________________ Model: '08 135i N54 6AT Coupe ///M Sport - E85 + 93 = E30 Mods: AA DPs + Gen I - BMS JB4 (Race + Map 2) + DCI + OCC - Cobb CP - ///M RSFB + Front Control Arms - Koni Yellow - Swift Spec R - Vorshlag camber plates - MPSS 225/255 - x-ph Angel Eyes 160w
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06-13-2015, 12:00 AM	#2
Cavpilot2k Chief Warrant Officer 1023 Rep 1,638 Posts Drives: like a damn lunatic Join Date: Feb 2012 Location: Boston iTrader: (0)	Hmmm. You know, I've never had that problem, but then again, if you clutch has no software, your clutch won't do funny software stuff... __________________ "Prius" is Latin for Eunuch. "Hrothgar": 2012 135i: 6MT M-Sport, BSM/Blk; Nav, Premium, Convenience, HK Dinan Stage 2 +PPK /// BMW PE /// VRSF CP /// K&N /// Koni Sports /// RSFB Inserts /// MPS4S 225/255 /// Other Stuff
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06-13-2015, 10:45 AM	#3
saace7 Private 7 Rep 90 Posts Drives: OneThreeFive Join Date: May 2013 Location: the world iTrader: (0)	OP has an AT but i see what you did there Is the slipping during WOT pulls/hard driving or during regular driving or both?
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06-13-2015, 04:30 PM	#5
Solo_M_Tech Brigadier General 1688 Rep 3,140 Posts Drives: 2014 M5 6MT Join Date: Nov 2013 Location: Massachusetts iTrader: (7) Garage List 2014 BMW M5 [0.00]	Torque converter/ transmission slip. Fluid/filter change may be needed. Each gear's clutch pack is slipping when engaged. __________________ 2014 M5 6MT
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06-13-2015, 09:13 PM	#7
Andrewcoja First Lieutenant 9 Rep 385 Posts Drives: 2011 135i MSport Join Date: Aug 2013 Location: Texas iTrader: (0)	AT doesn't have a clutch, it has a torque converter.
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