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      01-14-2009, 12:04 PM   #23
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Quote:
Originally Posted by rc'Z View Post
O-cha, please educate yourself, it works up, it works down:
http://en.wikipedia.org/wiki/Double_clutch
You should take you own advice, the transmissions naturally spins down for upshifts you catch it and double clutching would only add unnecessary steps and time. Vs downshifting where the transmission has to be spun up.

If you really think double clutching is going to be useful shifting to second in this car then your just a special guy really. Entertaining the idea any further would simply be ridiculous.

Next time try to use terms that you actually understand.

Oh and good job on linking a wiki article that backs me up, did you even read it?
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      01-14-2009, 12:05 PM   #24
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Hmmm, gues it works both ways... although I've never driven anything whose revs drop slow enough to facilitate a double clutch when shifting up (and I have driven big trucks before).
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      01-14-2009, 12:11 PM   #25
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Originally Posted by Hawkeye View Post
Hmmm, gues it works both ways... although I've never driven anything whose revs drop slow enough to facilitate a double clutch when shifting up (and I have driven big trucks before).
And especially not a performance car with a lighter than most drivetrain.
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      01-14-2009, 12:37 PM   #26
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O-cha it is difficult to read, but read the first three words:

When shifting up on a non-synchroniser equipped vehicle, the clutch pedal is pressed, the throttle is released, and the gearbox is shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the RPM will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manoeuvre can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.
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      01-14-2009, 12:59 PM   #27
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We're only talking 1st to 2nd gear changes as being an issue. Remember the difference in crank speed vs. gearbox speed is biggest in 1st gear (5th is 1:1 and 6th is overdriven). So it would seem a solution is to slow down the actually shift lever movement into 2nd's gate (fractionally) to allow time for the crank speed to reduce thereby minimizing the speed differential between the crank and gearbox. Not ideal for drag racing, but I don't drag race. I think double clutching is completely unnecessary in this application. You would achieve the same result by stopping the gear lever movement halfway before proceeding to 2nd's gate. Another solution of course is to not redline 1st gear. That's the best solution if you want your drivetrain to last (my preference too). I'd experiment if it wasn't winter and my car is essentially stored due to fresh snow/slush and summer rubber mounted.

Perhaps it's relevant to also consider why our cars came equipped with a CDV. The CDV limits shock to the drivetrain, and enables (keyword) BMW to make certain drivetrain components less stout (when equipped).
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      01-14-2009, 01:28 PM   #28
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This is a training issue, not a product issue.

Proper break-in plus proper shifting/clutching technique result in the ability to shift as fast as you want from any RPM without grinding gears or pulling the shift knob off its post.

And yes, I used to experience the grind...until I learned how the car likes to be driven. This is why magazine editors hate the Zed...because they can't just jump in and drive the way they think they know how to drive. The car has to be adjusted to, which takes time and effort, but the result of which is a harmonious mesh between driver and machine.
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      01-14-2009, 02:33 PM   #29
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Quote:
Originally Posted by rc'Z View Post
O-cha it is difficult to read, but read the first three words:

When shifting up on a non-synchroniser equipped vehicle, the clutch pedal is pressed, the throttle is released, and the gearbox is shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the RPM will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manoeuvre can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.
Seriously read the rest of your own article or actually evaluate what it says, you're so lost it's funny.


Quote:
Originally Posted by MVF4Rrider View Post
We're only talking 1st to 2nd gear changes as being an issue. Remember the difference in crank speed vs. gearbox speed is biggest in 1st gear (5th is 1:1 and 6th is overdriven). So it would seem a solution is to slow down the actually shift lever movement into 2nd's gate (fractionally) to allow time for the crank speed to reduce thereby minimizing the speed differential between the crank and gearbox.
You have arrived at the correct idea of a solution through incorrect logic. I misunderstood what you meant by crank vs gearbox speed at first, but the rest is still flawed a bit too. It's less of s retort as a better explanation of what you're trying to convey.


There are basically three free spinning parts in the driveline, the engine (and for ease of explanation) the "front" of the gearbox and the "rear" of the gearbox. The rear always moves with the wheels, the engine obviously always with the engine and the "front" which is what is free when the clutch is depressed and what the synchros are acting on to change it's speed. The actual gear change itself occurs between the "front" and the "rear" of the gearbox and the engine itself has nothing to do with it.


The 1st to 2nd shift is "special" because it's the widest ratio and what this means is that the "front" of the gearbox needs to slow down the most out of any gear change in order to meet the new speed of the "back" of the gearbox. This is because the 1st gear set is spinning at less than 1/4 of the speed of the engine, but the second gear set is spinning at a much faster at at less then 1/2 the speed of the engine if my memory serves me on our ratios. This means that in order for the "front" to meet up with the new gear set it must slow down a great deal by comparison with the other gears.

This slowing (or speeding up in the case of a downshift) is what the synchros are responsible for. As explained the 1st to second shift is what makes the most use of the synchros. So it needs the most time to adjust the speeds, which is why the idea of slowing down the shift is correct. The same effect can be done by shifting smoothly however since synchros don't like to be mashed together and that is what most people do in the 1st to second shift.

I'll edit some later for correctness of numbers, can;t be bothered right now.



This also highlights why it is ridiculous to double clutch an upshift like this as the "front" of the gearbox slows down much faster then the engine itself (so is more quickly able to be engaged then the rpms are to be at the new speed of the next gear) and you would just be slowing down the speed in which you could shift gear regardless of all the extra movements and steps you have to take.
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      01-14-2009, 02:49 PM   #30
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Quote:
Originally Posted by jragan View Post
This is a training issue, not a product issue.
It's both, all transmissions are like this from 1st to 2nd to an extent, a high RPM motor exacerbates the problem, it would be fixed with a higher number of cones but I doubt BMW sees an advantage to the cost since if your road racing your car you should never be shifting quickly from 1st to 2nd, or ever really be in 1st in the first (lol) place. Don't think BMW gives a dam about drag racing.
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      01-14-2009, 03:15 PM   #31
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I'm also under the belief that proper break in (run in) is essential. The break in period is just as important (if not more) to the gearbox as engine internals. Our cars have a 2 stage break in period. I'd speculate that most don't perfectly follow the first stage break in (1200 miles), and extremely few follow the second stage to the letter as it's over 2X the mileage of the first stage. I'm in stage 2 and following it to the letter. Overreving and too much load can't be good for the gearbox during this period. I'll finish the second stage and see if I ever have issues. Then again, I'm typically kind to my vehicles.
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      01-14-2009, 04:06 PM   #32
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This isn't the first car I've owned where tons of people complained about grinding into second gear. My experience tends to point to that people just need to adjust their approach to changing gears. I've never experienced grinding on any car I've owned, and I've owned a few where people claim the gearbox has issues.

And to say that double-clutching on a sychronized gear box is needed, that's just silly.
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      01-14-2009, 04:50 PM   #33
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Quote:
Originally Posted by rc'Z View Post
O-cha it is difficult to read, but read the first three words:

When shifting up on a non-synchroniser equipped vehicle, the clutch pedal is pressed, the throttle is released, and the gearbox is shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the RPM will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manoeuvre can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.
No BMW since the late 70s does not come equipped with synchronizers so this discussion is moot.

The problem here isn't that the 1st and 2nd gear ratios are too different. Synchronizers will ensure that the next selected gear is spinning at the same speed as the output shaft. There are two possibilities as to why there's a 1st to 2nd gear grind:

1: The 1st/2nd synchronizer is shot.

2: The input shaft is not completely disengaged when shifting.

It is entirely possible that the synchronizers on this particular transmission is defective, although if that were the case you'd hear a lot more than just the MZ4 drivers complaining about it since this particular model of ZF transmission is quite widely used. So that leaves the possibility of the problem being that the input shaft is not completely disengaged, meaning the clutch isn't completely disengaged when the shifting/grinding happened.

How much of this can be attributed to the CDV remains to be seen, but if you do a rapid 1st to 2nd gear shift right as you clutch in, it is entirely possible that the clutch hasn't fully disengaged yet before you put the car into 2nd gear, especially if the restriction in the CDV does not allow clutch fluid to flow through to the hydraulic TO bearing fork quickly enough to separate the pressure plate from the flywheel, resulting in the input shaft still receiving power from the engine.

I have yet to grind my 1st to 2nd shift in 2+ years of driving the MZ4 Coupe, then again I fully depress the clutch, wait a split second before I engage 2nd, even when I drive on the track (although on the track I would only make the 1-2 shift ONCE). Even with the CDV my first few events at the track shifting quickly between gears it has never been a problem.

(knock on wood)
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      01-14-2009, 06:14 PM   #34
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Quote:
Originally Posted by The HACK View Post
The problem here isn't that the 1st and 2nd gear ratios are too different. Synchronizers will ensure that the next selected gear is spinning at the same speed as the output shaft. There are two possibilities as to why there's a 1st to 2nd gear grind:

1: The 1st/2nd synchronizer is shot.

2: The input shaft is not completely disengaged when shifting.
While I agree with #2 (in fact on any other type of shift that's almost always the cause), but disregarding the wide ratio is incorrect, the collar is not completely blocked and if enough force is applied while not in sync the gear will grind.

More insight can be garnished from the fact that the grinding is actually very easily reproducible when shifting out of first in a high wheelspin situation of a burnout or drift where you're tires are moving quickly but the car is not. This effectively widens the gears even more by a pretty respectable amount.





It always amazes me how much the BMW community is numb to these sort of things which 90% of the the rest of the automotive community would quickly identify. I think it's the nature of the type which is an enthusiast who loves the car and driving, but doesn't work on their own car or get too much into the details.
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      01-15-2009, 04:58 AM   #35
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Quote:
Originally Posted by koala View Post
This isn't the first car I've owned where tons of people complained about grinding into second gear. My experience tends to point to that people just need to adjust their approach to changing gears. I've never experienced grinding on any car I've owned, and I've owned a few where people claim the gearbox has issues.

And to say that double-clutching on a sychronized gear box is needed, that's just silly.
Although it works with trucks, non-sycro square cut gears, and the like, it was a joke that a BMW would need to be double shifted to keep from grinding.
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      01-15-2009, 11:56 AM   #36
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Quote:
Originally Posted by F360C View Post
My brother went as far as to get his tranny replaced by BMW on their coin and to tell you the truth it really didn't solve anything. After 28,000 miles I have to say that the grind is I think paritally caused by shiffting technique... I have learned to be shift as fast as I want with out the grind but there is a certain way you have to hold the shifter.
How do you hold the shifter to avoid the grind?

I don't even have to rev high to get it to grind when I do a 1-2 shift.

1st gear, 3k rpm, clutch in full AND back off throttle, gear shift -> grind.

To expect a driver to have to WAIT A SPLIT SECOND before moving the clutch into 2nd gear is ridiculous, or a serious design flaw.
If that is the case with BMW, then so be it. I've driven alot of manual cars in my lifetime, without ever encountering this design flaw.
I wish BMW would just man up, and tell us exactly what the issue is, so we can get over banging our heads in guessing what the issue
really is.

Took it to BMW dealership, and I am hating the service department. They call it Driver Error, and that you shouldn't baby the RPMs. Told me to shift at higher RPMs. Total load of BS.
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      01-15-2009, 12:01 PM   #37
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Quote:
Originally Posted by O-cha View Post
While I agree with #2 (in fact on any other type of shift that's almost always the cause), but disregarding the wide ratio is incorrect, the collar is not completely blocked and if enough force is applied while not in sync the gear will grind.

More insight can be garnished from the fact that the grinding is actually very easily reproducible when shifting out of first in a high wheelspin situation of a burnout or drift where you're tires are moving quickly but the car is not. This effectively widens the gears even more by a pretty respectable amount.

It always amazes me how much the BMW community is numb to these sort of things which 90% of the the rest of the automotive community would quickly identify. I think it's the nature of the type which is an enthusiast who loves the car and driving, but doesn't work on their own car or get too much into the details.
Interestingly enough, if the gear ratios are the reason as to why the gears are grinding, we would also hear about it more from the E46 M3 owners (of which there are 100X more) since the gear ratios are virtually identical between the two cars (including the final gear and the overall tire size). If I'm not mistaken and are inclined to go look it up, I believe the ratios were only different by a few hundredth of a point between the two cars. I've not seen this type of complaint from E46 M3 owners.

Which then leads me to believe, that either MZ4 owners are just a whiny bunch (j/k), or my two hypothesis regarding the grind is correct. It's either an improperly designed synchro-mesh between 1st and 2nd, or operator error. Having had to work on cars A LOT and working in a small capacity with customer support in the automotive aftermarket industry, my suspicion is on operator error.

Either that or I don't drive my car "aggressively" enough.
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      01-15-2009, 12:29 PM   #38
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Quote:
Originally Posted by The HACK View Post
Interestingly enough, if the gear ratios are the reason as to why the gears are grinding, we would also hear about it more from the E46 M3 owners (of which there are 100X more) since the gear ratios are virtually identical between the two cars (including the final gear and the overall tire size). If I'm not mistaken and are inclined to go look it up, I believe the ratios were only different by a few hundredth of a point between the two cars. I've not seen this type of complaint from E46 M3 owners.
You are clearly very confused. I am not talking simply about the spacing but the spacing as it applies to the synchros, Just because a transmission shares the same spacing of gear ratios does not mean a thing.

The point is that things that increase the "work" of the synchros is wide spacing and high RPM changes (because gear changes being % based the higher the rpm the more inertia has to be combated for the same spacing)

This makes the 1st to 2nd shift at redline obviously the most strenuous.

The synchros on this transmission are obviously different then the e46, likely there is an additional cone on second gear (or two ) on the e46 M 6 speed, or they could be of different design.

Widespread grinding is a clear indication of inadequate synchros for the application (and/or driving style). I know no other automotive community that would dispute this point. It's pretty much a rock solid inference.
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      01-15-2009, 12:46 PM   #39
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I have a friend with a miata that has a totally shot 2nd gear synchros. HE HAS TO double clutch into 2nd gear.
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      01-15-2009, 05:57 PM   #40
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Quote:
Originally Posted by denial512 View Post
I have a friend with a miata that has a totally shot 2nd gear synchros. HE HAS TO double clutch into 2nd gear.
What was he doing, changing gears regularly without depressing the clutch pedal-- lol? (Before anyone says otherwise-- yes, you can change gears without the clutch pedal and yes, under the right circumstances you can do it very easily and without harm and no, I don't recommend doing it).
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      01-16-2009, 02:02 AM   #41
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Not sure.. but he got really good at double clutching.

Anyhow, I only purchased my 3.0si for a few months now, but it sounds like this 1-2 gear change issue is happening a lot. I'm surprised no one has a definitive answer to the question of what is causing it. Gotta be some mechanic that can figure what the real issue is, whether it be insufficient synchros, clutch drag, CDV causing premature wear on the oil and plates, etc..

If this were a honda, nissan, mazda, or any other cheaper car, I'm sure it would have been figured out already.
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      01-16-2009, 02:35 AM   #42
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When you say grind, do you hear loud grinding from the tranny itself, or is it that grind-ish feeling when you are pulling the stick into 2nd?

If it is the latter, it's pretty common from what I understand in a lot of transmissions and is due to the synchro design. It can also be avoided completely by not forcing the gearbox into 2nd so fast... you can feel when it wants to let you into 2nd and if you pause that tiny bit you wont grind at all. Unfortunately this makes smooth 1->2 shifts harder because the revs drop too quickly occasionally.

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      01-16-2009, 03:12 AM   #43
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Quote:
Originally Posted by chris719 View Post
When you say grind, do you hear loud grinding from the tranny itself, or is it that grind-ish feeling when you are pulling the stick into 2nd?

If it is the latter, it's pretty common from what I understand in a lot of transmissions. It can also be avoided completely by not forcing the gearbox into 2nd so fast... you can feel when it wants to let you into 2nd and if you pause that tiny bit you wont grind at all. Unfortunately this makes smooth 1->2 shifts harder because the revs drop too quickly occasionally.
basically you move the shifter toward the next gear. And put pressure on it, but don't push it in. When the 2nd gear synchros is ready, the shifter will pop into the gear(a little hard on our car. you really need a firm hand). Basically the more force you give it, the faster you can pop it in. But if you do it too fast, you can grind... because the synchros isn't ready yet.
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      01-18-2009, 05:23 PM   #44
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Well, I've owned my Z4 for about a year and had the second grind issue since the day I got it. Sure, I can delay shifting into second after I press the clutch down, and this results in a grind-less shift, but what's the point of driving a Z4 if you can't shift sportily into 2nd gear?

So, I replaced the CDV with one purchased from Zeckhausen. The CDV, at least in my case, is a major culprit for the 2nd gear grind. After replacing the CDV, I still have to delay my shifting into second but much less so than before. I'd say the delay is from a whole second to about half a second.

Then, I replaced the OEM transmission fluid with Royal Purple Synchromax. The improvement here is dramatic. Not only can I shift into 2nd even faster now, but the whole transmission is so much smoother. I'd say the transmission/gear box is much more communicative. This results in much less over and under revving when changing gears.

So, just get the CDV removed or replaced and go with a different transmission fluid. I went with RP Synchromax. I've read good things about Redline and Amsoil too.
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