# Will SMG wear out a clutch & syncros faster then a good MT driver?



## Moderato (Nov 24, 2003)

I drive an 04 330i 6MT and I've been wondering this about SMG cars. I did search for the answer but I didn't find anything specific. I know that when you're upshifting that if you let the rpms drop to about where they should be for the next gear and then let the clutch out you are minimizing the amout of slip that must occur in order to get the clutch to completely hook up. Now it's my understanding that the SMG can shift gears in milliseconds with the same tranny I have except the computer controlls the clutch. OK, so how can you upshift from 1st to 2nd in milliseconds without slamming the shifter into 2nd and practically poping the clutch? Some would consider this to be abuse on the clutch & syncros and uneccessary wear and tear, perhaps a service dept could try and deny you warranty coverage for driving your MT in this manner, but yet an SMG does this and it's considered a selling point?


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## STEVE46 (Aug 25, 2004)

SMGs use hydraulic or electric valves to operate the clutch and shifter. These are very quick acting devices but can also be slow acting. Because of this, the SMG can (and does) slip the clutch at certain times. Also, because the computer controls everything (including the throttle), the RPMs are just about perfectly matched for every shift. You don't even need synchros in this case. Heck, you can shift a manual transmission without the clutch if you can match the RPMs correctly. The SMGs computer does this, so there is no increased wear on the transmission. Finally, for downshifts, the computer will double clutch and blip the throttle to match revs. All of this is no great challenge for someone who drove a manual car before synchros were invented. I'd be willing to bet that the SMG box probably doesn't even have synchros installed.


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## Nick325xiT 5spd (Dec 24, 2001)

Answer: Yes.

Synchro failure is apparently extremely common in E46 M3s. My tranny went at a little over 4K, and I know of at least three other people who've had the same issue.


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## Nick325xiT 5spd (Dec 24, 2001)

STEVE46 said:


> SMGs use hydraulic or electric valves to operate the clutch and shifter. These are very quick acting devices but can also be slow acting. Because of this, the SMG can (and does) slip the clutch at certain times. Also, because the computer controls everything (including the throttle), the RPMs are just about perfectly matched for every shift. You don't even need synchros in this case. Heck, you can shift a manual transmission without the clutch if you can match the RPMs correctly. The SMGs computer does this, so there is no increased wear on the transmission. Finally, for downshifts, the computer will double clutch and blip the throttle to match revs. All of this is no great challenge for someone who drove a manual car before synchros were invented. I'd be willing to bet that the SMG box probably doesn't even have synchros installed.


 I hate to say it, but you have no idea what you're talking about.


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## Kaz (Dec 21, 2001)

No question. Just from feeling the way SMG shifts, you can tell there is going to be more wear than with a good MT driver. The transmissions themselves are identical for all intents and purposes, so there aren't any special parts installed or removed internally for SMG use. That's part of the market efficiency behind SMGI/II/SSG; BMW didn't have anyone develop a new tranny.

Having put a few miles behind SMGII and SSG, I'd say a SMGII will trash its syncros, whereas SSG will fry its clutch.


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## Tanning machine (Feb 21, 2002)

Kaz said:


> No question. Just from feeling the way SMG shifts, you can tell there is going to be more wear than with a good MT driver. The transmissions themselves are identical for all intents and purposes, so there aren't any special parts installed or removed internally for SMG use. That's part of the market efficiency behind SMGI/II/SSG; BMW didn't have anyone develop a new tranny.
> 
> Having put a few miles behind SMGII and SSG, I'd say a SMGII will trash its syncros, whereas SSG will fry its clutch.


I don't know what I'm talking about, but this answer (well, all the "yes, it will wear out faster" answers) seems counterintuitive. Why doesn't the SMG system do as well as a good MT driver, if not better (i.e., never makes mistakes)? In principle, it should have perfect timing for everything, not allow misshifts, will rev-match and double (de)clutch.

Now, perhaps by "good" MT driver you mean one who doesn't mash the tranny around, and with SMG one might have the tendency to make quick shifts, or high-rev downshifts, or use other techniques that increase clutch wear. But it would seem to me that a well designed SMG system should impose no more clutch wear than a similarly driven MT (i.e., similar aggressiveness).

What am I missing?


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## Kaz (Dec 21, 2001)

Tanning machine said:


> I don't know what I'm talking about, but this answer (well, all the "yes, it will wear out faster" answers) seems counterintuitive. Why doesn't the SMG system do as well as a good MT driver, if not better (i.e., never makes mistakes)? In principle, it should have perfect timing for everything, not allow misshifts, will rev-match and double (de)clutch.
> 
> Now, perhaps by "good" MT driver you mean one who doesn't mash the tranny around, and with SMG one might have the tendency to make quick shifts, or high-rev downshifts, or use other techniques that increase clutch wear. But it would seem to me that a well designed SMG system should impose no more clutch wear than a similarly driven MT (i.e., similar aggressiveness).
> 
> What am I missing?


With SMGII, the way it slams through gears can't be good for the syncros. It's probably OK on the clutch, but it does seem to beat on it on upshifts.

With SSG, it seems to slip the clutch like mad on standing starts and mid-speed upshifts. It feels like a 16-year-old driving a MT Honda.

A good (not abusive) MT driver is going to know what 'feels right' for every given situation. A computer, at least in combination with the way SMG/SSG works, can't possibly.


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## James (Jun 30, 2004)

Nick325xiT 5spd said:


> I hate to say it, but you have no idea what you're talking about.


 : popcorn:


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## Nick325xiT 5spd (Dec 24, 2001)

SMGII uses the synchros to make its shifts. SMGIII is the same way--BMW stated that they backed off on the shift speed because it was breaking trannies.


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## allaboutme (Dec 22, 2003)

Nick325xiT 5spd said:


> SMGII uses the synchros to make its shifts. SMGIII is the same way--BMW stated that they backed off on the shift speed because it was breaking trannies.


Is the speed shift the 80ms shift times? If so, is that why Ferarri uses ~150ms times?


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## STEVE46 (Aug 25, 2004)

Nick325xiT 5spd said:


> SMGII uses the synchros to make its shifts. SMGIII is the same way--BMW stated that they backed off on the shift speed because it was breaking trannies.


Hmmm... I don't think so. They actually made the new SMGIII gearbox shift faster. It's gear changes are around 60ms in the new M5. Also, World Rally Car teams have found that their SMG cars have LESS wear on the gearboxes than their normal manuals do.


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## Kaz (Dec 21, 2001)

STEVE46 said:


> Hmmm... I don't think so. They actually made the new SMGIII gearbox shift faster. It's gear changes are around 60ms in the new M5. Also, World Rally Car teams have found that their SMG cars have LESS wear on the gearboxes than their normal manuals do.


Rally cars have true sequential transmissions. BMW SMGs do not.


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## allaboutme (Dec 22, 2003)

Kaz said:


> Rally cars have true sequential transmissions. BMW SMGs do not.


From all online accounts, it seems BMW made a true sequential for the m5 and m6 with that strange shift pattern.


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## Kaz (Dec 21, 2001)

allaboutme said:


> From all online accounts, it seems BMW made a true sequential for the m5 and m6 with that strange shift pattern.


I'm still looking for a pic of the inside of a SMGIII that has the shift drum of a sequential.

If SMGIII can skip gears like SMGII, it can't possibly be a true sequential.


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## Nick325xiT 5spd (Dec 24, 2001)

STEVE46 said:


> Hmmm... I don't think so. They actually made the new SMGIII gearbox shift faster. It's gear changes are around 60ms in the new M5. Also, World Rally Car teams have found that their SMG cars have LESS wear on the gearboxes than their normal manuals do.


 Which is well back from the 45ms shift speeds the system is capable of.


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## Kaz (Dec 21, 2001)

Oh, also forgot to mention that racing sequentials don't bother with syncros at all, since it's just another thing to wear out.


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## Stuka (Jul 17, 2002)

Nick325xiT 5spd said:


> Answer: Yes.
> 
> Synchro failure is apparently extremely common in E46 M3s. My tranny went at a little over 4K, and I know of at least three other people who've had the same issue.


 

I didn't exactly baby my M3 when I had it, and other than having to disconnect the battery once to reset SMG, I never had a problem with synchros or what not.

Granted, I only had 30K on the car, but I had the second oil service done in that 30K miles according to the computer. :bigpimp:


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## Stuka (Jul 17, 2002)

Kaz said:


> No question. Just from feeling the way SMG shifts, you can tell there is going to be more wear than with a good MT driver. The transmissions themselves are identical for all intents and purposes, so there aren't any special parts installed or removed internally for SMG use. That's part of the market efficiency behind SMGI/II/SSG; BMW didn't have anyone develop a new tranny.
> 
> Having put a few miles behind SMGII and SSG, I'd say a SMGII will trash its syncros, whereas SSG will fry its clutch.


Except according to BMW, SMGII programming included double clutching for every gear change. :dunno:


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## Stuka (Jul 17, 2002)

allaboutme said:


> From all online accounts, it seems BMW made a true sequential for the m5 and m6 with that strange shift pattern.


The BMW sequential gearboxes are "sequential" in that you execute one gear change per tap.

But it is NOT a true sequential box in the same sense as the ones found in race cars, in that those things gots no synchros.

With regards to SMGIII. All BMW did was rearraged the gears in a non-H pattern so that 1st and 2nd gears can be beefed up to take the extra abuse. :thumbup:


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## Nick325xiT 5spd (Dec 24, 2001)

Stuka said:


> I didn't exactly baby my M3 when I had it, and other than having to disconnect the battery once to reset SMG, I never had a problem with synchros or what not.
> 
> Granted, I only had 30K on the car, but I had the second oil service done in that 30K miles according to the computer. :bigpimp:


 Well, all I can say is that I PERSONALLY KNOW four people who have had synchro failure in their M3s.

It's also a pretty common issue on roadfly.


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