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04-09-2013, 07:46 AM | #243 | |
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04-09-2013, 01:40 PM | #244 | |
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1. The "issue" is really two issues. The first is the 3->2 rejection during off-canter or high speed cornering. This is not common and is only reported by track junkies. This appears to be fixed by using the stiffer engine mounts. The second issue is the 1->2 grind which you can work around by doing a heartbeat pause. You will probably not run into this as it's only reported by M owners on the forum so far. Seeing as the 1->2 shift can be made faster with better engine mounts, this would point that the issue is either: a. The twisting of the engine in relation to the gearbox is changing the geometry of engine -> gearbox causing the linkages to not match up properly. b. A combination a. and a mechanical issue with the gearbox. If it was purely a mechanical issue with the synchros, then stiffer engine mounts wouldn't have made any difference. It also wouldn't make a difference if people pulled the shifter hard down and to the left (which is another solution people use). It would also be reported by all owners, not just M owners as the same 6 speed transmission is used on all Z4s. 2. Stiffer transmission mounts does not solve the issue. There are lots of threads detailing upgrading the transmission mounts, and most of them report less of a change than the engine mounts made with greater increases in NVH. I always take info from vendors with a grain of salt. However, the info from vibra explains why upgrading the mounts with stiffer mounts on the existing mounting geometry doesn't make much of a difference on the transmission movement, but increases NVH. This explanation coincides perfectly with people's experiences. I also ran it by a friend of mine who is an excellent mechanical engineer in the automotive industry, and he agreed with it. Seeing as the theory matches up with practice, and that they delivered excellent engine mounts (that completely transform the car) with almost no increase in NVH, there's no reason not to believe that they know exactly what they're talking about.
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04-09-2013, 02:22 PM | #245 | |
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A gearbox has an cast aluminium housing which is bolted to the block with 10 bolts or so. Any twisting in that construction would cause the gearboxhousing to crack, the clutch to break, the block to crack, the bolts to break or the crank to break (or any combination of those ). I think I can pretty shurely say that it is 100% impossible for the engine ->gearboxconnection to have any flex. Also there are no linkages to the gearbox: it is 1 linkage. That is connected to the shift lever. When the engine-gearbox assembly moves for say 10mm, the shifting in eg. 2 shifts accordingly. The shift mechanism itself is suspended in a rubber bushing (shifting arm bearing), so it flexes all the time. Even when you shift gears when stationairy. When you shift in another gear you always use the tactile feedback from where the shifter was in the previous gear. Whatever the reason for grinding 1->2 is (and I'm pretty shure I know what the reason is), it's absolutely impossible that it's from twisting of the engine in relation to the gearbox. And 3->2 denial is driver error; not using the feedback from the stick and just yanking it in a place where the gear simply isn't located. If you want to know why 1-2 is grinding, you first have to know why and when a gearbox grinds its gears, and that is not an issue with gearbox suspension or flexing of the engine-gearbox assembly, cause that last one is plain impossible unless you're in a serious crash. It's a synchro problem. I'm not saying that stiffer gearbox mounts (or engine mounts) have no advantages, because a stiffer suspension reduces the pendulum effect from the assembly which makes the whole car for a more stable platform (the same reason why eg. a fluel truck has bulkheads in its cargotank; without that it would tip over in the next corner.). But you won't reduce grinding gears, and if you can't find the gears: learn how to shift.
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04-09-2013, 03:09 PM | #246 | ||
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The question is does the shifter linkage move as much as the engine/transmission do? Because as you say: Quote:
And yes technique can solve the issue. No reason not try to upgrade it so you can shift faster and more easily during high performance driving. The engine mounts already made a big change.
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04-09-2013, 03:13 PM | #247 | |
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For 3rd to 2nd, the gate is located to the left of the furthest point of the shifter travel under high load and lateral G. That means it's not accessible. A shift gate that moves to another country and can't be found doesn't equal driver error, it's drivetrain torsion/slop due to inadequate mounts. It's a design flaw. One that can be remedied with proper mounts. For 1st to 2nd, yes, it may be a syncho problem, it may not. Have you seen the ancient threads from about 4-5 years ago on this? (About 8 of them, here's one.) The question we need to answer is why does pulling the shift level down and to the left eliminate the grind in many cases? I've never had the car grind once after I started doing that, and had it grind twice before I used that method. Did the synchos repair themselves, or did the mechanical action of pulling to the left affect something? If pulling left helps (and it does), and if the issue occurs under high load high RPM (it does), then isn't it just possible--however unlikely--that torsion due to load is somehow affecting the linkage/shifter/transmission? There have been those folks who, despite trying the "pull left" approach continued to have issues. Some had their transmissions replaced under warranty, which "fixed" the issue. So, in some cases, yes, synchros. In others, well, clearly not the case since synchros issues don't get better over time, and pulling left didn't repair them. |
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04-09-2013, 04:05 PM | #248 | |
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Yes I know as I displayed my reaction on them seperately
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Even reverse is situated next to that fork, and then there is about 1" room. No way the engine/gearbox assembly can rotate/shift that much! Between 2nd and the shift gate edge is about 3,5cm space (I can only extract form your post that the lever can't access 2nd because it's limited by the shift gate edge). I've just measured the height between shift gate edge and the mount rubber is about 30cm, and the width between both rubber transmission mounts is about 25cm. The width between the engine mounts is about 65cm. (I'm sitting here next to my z4 which is on the carlift, so I'm measuring these numbers as I type ) That means that when the shift lever moves 3,5cm, the compression (push pull difference) of the transmission mounts is (3,5/30)*25=2,9cm, but the same push pull difference in the engine mounts has to be (2,9/25)*65=7,5cm No way that the transmission mounts are that much compressed. As the engine is about 55cm of height above the engine mounts, it would mean that the engine would have to shift (3,5/30)*55=6,4cm sideways in order to get the corresponding effect on the shift lever. (remember it's a rotational force, both the high load and the G force yanking on the engine block) The edge of my ESS supercharger assembly is situated about 3cm from the chassis suspension strut well, so in order to get that amount of gear lever shift (for 2nd gear not to be accesible) the supercharger assembly would have to ram itself 3,4 cm through the chassis... That's just plain ridiculous imho. Whatever it is that some people can't get the lever into 2nd: I doubt it's that. I hope you can follow and picture the math I displayed. Also there is another effect that even further limits the movement of the shifter in relation to movement form the gearbox, and that is that the shifterball is situated in the shift arm. The shift arm is a connection between the gearbox and the chassis. That means that the shift arm hardly moves. What happens when the gearbox underneath moves to the left (so that 2nd would eventually become inacessible), the shift stick itself will bend to the right. Look in TIS for the exact layout from the components. So I think that it is even sheer impossible for the shif lever to even touch the side. And as always: 2nd is about 2cm to the left from 3rd, but than down in stead of up So the only thing you gain with stiffer engine and transmission mounts is a more stable platform. Not that that's a bad thing; the transmission and engine mounts are soft (normal car style), so you can feel the mass wiggle beneath you when you corner and on bumpy roads.
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Last edited by GuidoK; 04-09-2013 at 04:30 PM.. |
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04-09-2013, 07:07 PM | #249 |
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So, boiled down, that analysis and math contends that gear selection position can't move much, and there are physical limitations to how much movement the mechanical systems have available in terms of tolerance. Okay fair enough.
But that doesn't get us to a solution. And that is what most of us are after. Here are the data points we have, along with the most reasonable solution to the following issues: Issue - 3rd to 2nd 3rd to 2nd is an issue. It's not driver error, unless half the forum (and quite a few other forums) don't know how to shift this car or other BMWs.Issue - 1st - 2nd Pulling down and to the left helps, and in many cases eliminates 1 - 2 grind. Many report this, and it can't be discounted. It's possible that in learning to pull down and to the left folks, have learned to work around a synchro limitation (so the user has modified more than just pulling to the left, maybe waiting a bit and allowing things to "catch up"). That would support your synchro contention.Regarding 3rd to 2nd, the aftermarket community says pretty much the same thing across the board. The solution being offered by Turner Motorsports, Vorschlag, UUC, AKG, Rogue (1, 2, 3, 4, 5) all work on the same premise and offer the same solution. (I seriously doubt the customers who bought these products--and report improvements--are all wrong or that they're all in league with vendors.) If the evidence in front of us shows that the 3rd to 2nd issue can be improved, if not corrected, with improved mounts, and that the same solution may help or improve the 1 -> 2 grind, why not just run with the solution and call it a day? Last edited by Finnegan; 04-09-2013 at 07:35 PM.. |
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04-09-2013, 07:54 PM | #250 | |
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[QUOTE=Finnegan;13791699]Again, two separate issues here. 1st to 2nd, 3rd to 2nd.
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04-09-2013, 08:10 PM | #251 | |
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The 1st-2nd grinding is definately a synchro problem (the grinding teeth are a dead giveaway . You say synchro's don't repair themselves, but maybe they are not broken? As I understand it happens during acceleration, mostly full throttle (obviously) and primarely with /m cars and less with normal cars who use the same gearbox. Although that last remark is not completely true: the GS6 box is a co-production between ZF and getrag (it's zf design though). the GS6-37BZ units are afaik ZF and the GS6-37BG units are Getrag made (the letters Z and G are a giveaway ). So that might be a reason some experience it and others dont (difference in production tolerances etc; the boxes should be the same but you know ). A second difference is that m cars (s54) rev much higher; the diff ratio is also much bigger. So the speed difference between a running gear and a stationairy gear is much bigger. And that's what a synchro has to overcome. Maybe they are not fully up to the job. Where the problem lies in the synchro's: I don't know. It could be a number of places: The synchromesh consists of a synchronizer hub (with inverted cone) that sits on the splined output shaft (the splines make it a solid connection that can move forth and back). Around the synchronizer hub sits the synchro sleeve (also connected with splines to the hub), and that sleeve is centered with springloaded balls. When you shift and you feel the click that the transmission falls into a gear, you feel that the synchro sleeve shoots out of a groove which was held in place with those springloaded balls. That happens after the synchro cones where pushed together to match the speed difference. If the groove is too wide for those balls, the sleeve can move around, and maybe that causes the grinding (the sleeve moving foreward a bit and hitting the gear before the synchro's had the chanche to fully revmatch)? And in the synchro sleeve is another groove in which the shiftfork sits. Maybe that is too wide and pushing the lever to the left pushes the shiftfork a bit against the synchro sleeve so it cant wobble around? Anyway: none of these potential problems with the synchro can be fixed with stiffer transmissionmount bushings imho. Its a problem with teeth of the synchro sleeve touching the teeth of the drive gear too soon for the speed being matched up by the synchro (the cone and inverted cone pressed together). I can't imagine how a bushing can influence that. If you want to be shure not to grind the teeth, imho you have to double clutch, or adjust the rev range (more rev matching), or do something to the synchro's etc. But by all means be free to experiment. I'm more of a think before you try kind of guy The thing that sometimes bothers me is that I see/read explanations presented as facts by people which are completely impossible and make absolutely no sense. But... that's the internet. I have to live with it
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Last edited by GuidoK; 04-09-2013 at 08:38 PM.. |
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04-09-2013, 08:19 PM | #252 |
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It feels to me like the linkage blocks under braking force at the track - sometimes street too. It's like no matter what I do I cannot get the car into second gear many times. I'm hoping my new AS shifter and the Vibra mounts correct it. I already have stiffened tranny mounts and alternate fluid in the transmission. At the end of the day I've always believed the unit itself is Fcked...
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04-10-2013, 05:22 AM | #253 |
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someone should get a DCT unit from the E92 and try to mate it with the S54 and fit it in our cars.
This i will buy. If not, when my transmission is broken, I will open it and figure out how to increase the tolerances slightly and fix the syncros into a better design. Then write a DIY and charge everyone money for the parts :P |
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04-10-2013, 07:39 AM | #254 |
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Did my first "launch" with these mounts on sunday.... hmmmm interesting......
so with the stock mounts.... id set of and once the wheels broke traction their was enough engine movement for certain parts of my s/C parts to Brush the hood... Also a very unpleasurable feel from the car itself.... Now im guessing the 10/15 or so trackdays ive done is what killed my 10k mile stock mounts which were split right round the base of the mount...... now.... onto sunday.... 10 deg C day, lovely and bright and dry, motor and tyres nice and warm by this point!! so i stop in the road.... gently let the clutch out so the car is rolling on idle then mash the gas pedal to the floor..... the car lights up the tyres in first, change to second, same..... but it was such a smooth experience....i stop down the end of the road and open the hood, no more contact with the underside at all under the extremes of use and the engine control actually makes the car feel SMOOTHER under these hardcore situtions.... so so so pleased with these mounts and the competition units was 110% for me the right choice.... slowing down brings a resonance/ vibration to the cabin.... but its very very minor.... Re shifting?... my car has never had the grind issue, shifting always felt nice and i love the action of the z4m gearbox.... really looking forward to my first track-day with these on!! They definitely add to solidity of the drivetrain and for what ever reason.... shifting does feel easier under the extremes of use... one thing i am noticing is a break in traction more/easier?? possible or placebo effect??
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04-10-2013, 08:43 AM | #255 |
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that's because you drive on the wrong side, so shifting in 2nd will force you to push left :P
My car sometimes have a grind even when i'm pushing left and downwards in 2nd gear and i believe strongly that my engine mounts are toast bread with butter and jam. |
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04-10-2013, 10:48 AM | #256 |
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heres a pic of my stock units..... the split one was from the exahust side, the split runs round the complete circumference..... this car has 11k miles in total and around 4000 of those are supercharged miles.... That particular mount had been heavily compressed too....
IMO .......... if your supercharged this should be part of the s/c installation.... im not saying VT mounts but.. stiffer mounts at least..... cars first proper outing!! attracting atention as always!!
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04-10-2013, 11:13 AM | #258 |
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Byron, are those still the CSL's or have you swapped to other wheels?
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04-10-2013, 11:34 AM | #259 | |
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Also have 18s but i cant feel any difference on the track so tend to leave the CSLs on... they are strong as fuck!
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04-10-2013, 11:39 AM | #260 |
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The dish on the rear wheels looks so good hence my question, i've seen CSL's in person before but i never noticed them having such a great rear dish. If i'd got a track i'd go 18", perhaps Team Dynamics Pro Race 1.2 though i'm not sure if their offsets fit our cars.
edit: sorry for the hijack. I wont be posting off-topic here anymore
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04-10-2013, 11:42 AM | #261 |
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...and received them yesterday. Quick turnaround!
Does anyone know if I would be able to install 1 mount at a time? I'd like to install the intake side mount this weekend when I replace my leaking Power Steering line, and install the exhaust side mount in a month or 2 when I install headers. I can ask Vibra Technics, but I figured I'd tap into forum wisdom as well. |
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04-10-2013, 11:45 AM | #262 | |
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whooopppss thread back on track sorry guys!!
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04-10-2013, 11:47 AM | #263 | |
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04-10-2013, 09:17 PM | #264 |
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There will always be people that use their supposed 'knowledge' to mock / pish-posh any particular products successes. Having zero HANDS-ON experience, they'll quote all sorts of personal opinion to shore up their argument. They won't put any stock in the fact that many intelligent forum members here have actually installed the product and formed their opinion around the only fact that matters in the end: real-world user experience (and not some sales pitch from the retailer).
I went through the same thing with the RE Race Brace. Now I just nod and laugh at the supposed know-it-alls. IMO, buy one and form a REAL opinion, or stfu before you slag a product that actually works. |
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