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Discussion Starter #1
Hello all,

I'm new to this car, and SMG in general. So, maybe it's me, but every once in a while, say once a week at least, I get a bang when starting off that feels like the "rear ended feeling" people on here describe. It's always from a dead stop, and always when I am just driving off normally (not red-light drag racing). Feels like when you're learning to drive stick and you let the clutch out too fast!

No warnings, no red/yellow cogs of death, just the occasional rear ended feeling when starting off in first from a stop.

Anything I'm doing wrong? Can I control this at all?

Thanks!!

Steve
 

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Are you applying the brake at the red light? You have to keep your foot on the brake the whole time then when you release the brakes the car will assume you're getting ready to take off so it'll engage the gear like normal without a bang. Otherwise it'll just dump the clutch if you don't.
 

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Are you applying the brake at the red light? You have to keep your foot on the brake the whole time then when you release the brakes the car will assume you're getting ready to take off so it'll engage the gear like normal without a bang. Otherwise it'll just dump the clutch if you don't.
Interesting.... i have the same issue the OP stated above, and i do tend to take my foot off the brake when at a stop light. Sometimes it feels like the rear end is going to fall off it is so violent. Since i think the clutch is close to the end of life (shuddering in 1st and 2nd takeoff) i thought it was a clutch engagement problem.i will keep an eye on this, thanks for the heads up.
 

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Interesting.... i have the same issue the OP stated above, and i do tend to take my foot off the brake when at a stop light. Sometimes it feels like the rear end is going to fall off it is so violent. Since i think the clutch is close to the end of life (shuddering in 1st and 2nd takeoff) i thought it was a clutch engagement problem.i will keep an eye on this, thanks for the heads up.
Yep, if memory serves me right it goes into neutral instead of holding the clutch when you sit at a stop light for extended amount of time without applying the brakes then when you hit the gas it engages first gear and dumps the clutch.

There was another thread recently on here with the same problem and the OP doesn't have the problem anymore after applying the brakes at stop lights.
 
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I get the bang once in awhile but it's my fault as I take my foot off the brake and let the car drop into neutral or disengage completely out of gear.
 
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^^ all this! Foot on brake at all times.. Or if you do sit at lights when your foot off the brake, apply the brake first then get on the throttle before moving.
 

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Discussion Starter #7
Holy sh*t, thanks guys. I'll definitely give this a try. I never read that anywhere, and I've been through several hundred pages of tech pubs that were posted in the stickys somewhere. That is absolutely crazy, but it makes sense that with the brake release, the clutch has time to predict a request for engagement, otherwise it has no idea when you plan on hitting the gas.

Will do this and see what happens. I'll make sure to engage the brakes before setting off, if I do have to sit at a light for extended periods of time. Every time its happened, it was always while waiting for a light to change, and most likely with foot off the brake (again, a habit carried over from manual transmission driving).

Will keep you all posted.
 

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what a great thread , as i think i do this also . Sit at the lights with no brake on and it gives a bit of a bang when set off sometimes . Dam so simple !!
 

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Yep, I'll confirm the same here. I was hoping it'd go away after the clutch job but even with a new clutch, flywheel, SMG pump, slave cylinder and misc other parts it still does this if I take my foot off the brake for more than ~10 seconds at a light. Oh well, I'll just call it a "personality" trait. hiha
 

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respectfully i disagree with the advice given so far. if you have a hard bang...a violent one like someone slammed into your rear end...its not a foot-off-the-brake issue.

its a larger issue. i dealt with it on my car for months until it got so bad that my transmission went out completely. my issue was a tale tale sign of a clutch position sensor that was on its way out and ultimately failed.

there was no coding or clutch adaptations that could fix it. once it went, it had to be replaced. otherwise with increasing frequency if i didnt FEATHER the gas pedal from a dead stop until the clutch was fully engaged, it would BANG into gear violently.

ultimately i replaced everything connected to it: the clutch position sensor, the throw out bearing / clutch release bearing (which was totally shot btw), new clutch, new flywheel, SMG fluid flush, EURO smg flash and new adaptations.

now it shifts perfectly again. i wouldnt try to write this off as a braking issue....its far more complex than that if you are indeed experiencing slamming into gear. good luck out there fellas...
 

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Discussion Starter #11
^^ Agree with this guy. Let me be sure to clarify, its a jolt but not a real severe one that some describe. It just doesn't feel like the usual set-off. Easy enough in my case to sort out, because if it still happens after I modify my technique, then it is another issue like mentioned above. It ONLY happens when setting off in first from a dead stop, and I DO sit with my foot off the brake, carried over from normal MT driving habits. It NEVER happens in between gears and I have no other abnormalities noted with the shifting.

Just to be clear, in case someone is having something else going on with theirs...
 

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Had the same thing happen to me when I first got the car. I was used to driving true manuals and usually would have my foot off the brake. Keeping my foot on the brake has eliminated that jolt.
 

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Discussion Starter #13
Had the same thing happen to me when I first got the car. I was used to driving true manuals and usually would have my foot off the brake. Keeping my foot on the brake has eliminated that jolt.
I love it. This week can't happen fast enough. I sooo hope this works for me!
 

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First try resetting your SMG by rolling at about 20mph and holding both paddles in for about 5 seconds (it's been a while so I may be incorrect about how long you hold the paddles in). If that doesn't fix your problem I would assume it is your clutch position sensor. I had the same issue and thats what it turned out to be. Got it replaced and haven't had any problems with that since. Replaced at 64k, now at 69k.

EDIT: Before I got my CPS replaced, there would be times where there would be a perfect transition between stop and go in first gear, and other time where I felt like I was rear-ended by a vehicle going about 5mph behind me. Eventually it go so bad that the CPS failed, and the car would completely stall every time. CPS replaced and everything was perfect.
 
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Great info to know .. thanks . Checked mine out this morning and no jolting .... but will do some more tests.
 

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yup, sounds like we had the same exact issue. unfortunately for me....i replaced a ton of parts including clutch and flywheel before realizing it was the CPS. probably could have saved myself an easy $2k but oh well, the clutch and flywheel are brand new now. ive only put like 1200 miles on the entire system since it was replaced a few months back in the spring or so...

OP good luck with the diagnosis!




First try resetting your SMG by rolling at about 20mph and holding both paddles in for about 5 seconds (it's been a while so I may be incorrect about how long you hold the paddles in). If that doesn't fix your problem I would assume it is your clutch position sensor. I had the same issue and thats what it turned out to be. Got it replaced and haven't had any problems with that since. Replaced at 64k, now at 69k.

EDIT: Before I got my CPS replaced, there would be times where there would be a perfect transition between stop and go in first gear, and other time where I felt like I was rear-ended by a vehicle going about 5mph behind me. Eventually it go so bad that the CPS failed, and the car would completely stall every time. CPS replaced and everything was perfect.
 

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Copied my response from another thread, since there are about 80-billion threads on this issue:

First off, the SMG reset is 2 seconds, not 5, 10, 8 or whatever it is people say. I don't know how the number has evolved so much over the years - the manual clearly states 2 seconds. Second off, this does NOT reset the SMG. It's not a fancy fix-all reset - all it does is calibrate the rollout of the tires so the torque calculations the SMG performs are accurate. You do this reset whenever you get new tires put on the car.

A proper SMG "reset" is really called SMG adaptation and it resets the clutch engagement and shift gate calibration of the car, and must be done with the car hooked up to the proper software. However, this is someone you will want to look into and have the adaptation done when the car is nice and hot and you've gone through the gears. Not with a cold clutch or else everything will be off. If I remember right, doing this also clears out any and all "learning" the SMG has done to get to know you as a driver. The SMG system tries to learn the way you drive so that it drives better with you. It watches how you drives and adapts. Right now, it remembers whoever used to own the car. It has to learn you. (FYI - it has one profile per key, so make sure you are always using the same key, and if someone else frequently drives the car, let them have the other key and let these keys be "assigned" as everything from seat position and radio stations to climate control preferences is also unique to each key).

Lastly, you'll want to have Euro-SMG coding put on your car as soon as you can. Because US-Spec cars had the free maintenance, BMW gave us a different SMG programming that sacrificed shift comfort for clutch preservation to avoid having to install a new clutch. Long story short, it makes the car shift like crap. Once you get the Euro software on there the car will drive much better and you will totally say this is how it should have come from the factory (and it did! - just not in the US lol).

Finally, now that you know all that, I will say that it takes some getting used to (it's a learning curve for both you and the car), and it also helps for you to understand how the SMG works and thus its limitations and your expectations. Right now I'm talking about D mode.

The SMG is NOT an automatic. Automatics have it much easier since everything they do is smooth - why? Because a torque converter has very little back-torque transfer under normal conditions. The SMG is a clutched manual, and thus it has full back-torque transfer so you feel every slip, lurch, and clunk from those clutch engagements. This about how it works - the SMG is basically a guy with a clutch on one foot and a gear shifter in his hand, watch you apple gas and throttle. He looks at engine RPM, throttle input, and current gear to determine what to do. The SMG WILL NOT UPSHIFT unless you are giving it some sort of throttle. You cannot rev it out the 7K, then completely cut throttle and expect it to upshift. It will not do that. I think this is the biggest difference between it and an automatic in terms of programming.

The Drivelogic mode you are in (D1 - D5, or otherwise, D mode, however many bars are lit - NOT the gear indicator to the left of "D" on the instrument cluster) determines the base aggressiveness of the shift program. D1 will will generally be very conservative and shift as early as possible. D5 will try to hold gears and will wait a long time to upshift. You must choose the settings to your driving style. If you are on the autobahn and just slaughtering traffic, D5 might be great - it always downshifts aggressively upon strong throttle application and shifts late and generally shifts quickly. Choose D5 when you're creeping in traffic and you'll want to get out and start kicking the car. In a general sense though, don't use D1 as it starts in 2nd gear and fries your clutch.

My personal preference is D2. I use it in conjunction with P500 (not P500S). D2 shifts relatively early and is smooth, but having it in P500 helps with getting some torque out of the motor. P400 is far too desensitized, in my opinion.

When you eventually get the feel of the car, you'll be able to "tell it to shift" even with D. I now will roll into the throttle and then lift slightly when I want the car to shift. It does so perfectly even in D mode. Also, this means that YOU are still in command of the shift timing of the car even with it in D (you are just using your foot rather than your paddles). I think this is one of the biggest frustrations of SMG, is the car being in the middle of a shift when you need to make a move. This helps alleviate that problem.

Now, for when you are driving in manual mode, by all means feel the car like a manual. Upshift whenever you feel it's the right time. When I drive with this intent the car never gets shifted before 5K, and the car is almost always about 3500RPM. It just feels more alive and ready. Not practical for mileage, no, but I leave it in D to get better mileage. Second, let the car do the work for you. The car will not let you downshift to 1st gear at 80mph on the highway, so if you need max acceleration, just pull the downshift paddle like 10 times and mash your foot once you year the RPMs jump up to the characteristically correct sound. You'll get your acceleration without the BS of having to do quick math to see how many gears you need to go down.

Lastly, and this is really just getting used to the characteristic of an S85, is that the S85 is naturally a high revving motor. It likes to be revved out. In your E39 I'm sure you were used to using that great bottom end and broad mid range to leisurely pull the car everywhere - the S85 is not like that. The S85 wants you to use its rev range. That is where its power comes from. From 3K+ the car wakes up from 6K+ the car just enters rabies mode and all hell breaks loose in the best way possible.

I know this was a long post but I hope it helps you get to know your SMG better. Personally, I love the SMG and think it's an amazing transmission that helps you get the most out of the S85. When the SMG is working correctly, it's amazing how smooth it can be, and at the same time, how brutal it can be in S6 when you're going through the gears.
 

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+1 all these years of driving this car and still learning new things... amazing!
 

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respectfully i disagree with the advice given so far. if you have a hard bang...a violent one like someone slammed into your rear end...its not a foot-off-the-brake issue.

its a larger issue. i dealt with it on my car for months until it got so bad that my transmission went out completely. my issue was a tale tale sign of a clutch position sensor that was on its way out and ultimately failed.

there was no coding or clutch adaptations that could fix it. once it went, it had to be replaced. otherwise with increasing frequency if i didnt FEATHER the gas pedal from a dead stop until the clutch was fully engaged, it would BANG into gear violently.

ultimately i replaced everything connected to it: the clutch position sensor, the throw out bearing / clutch release bearing (which was totally shot btw), new clutch, new flywheel, SMG fluid flush, EURO smg flash and new adaptations.

now it shifts perfectly again. i wouldnt try to write this off as a braking issue....its far more complex than that if you are indeed experiencing slamming into gear. good luck out there fellas...
For what it's worth I think you're describing a different issue. I had my CPS replaced with my clutch/flywheel and I still get this "bang" if I sit with my foot off the brake at a light for an extended period and then hit the gas without touching the brake first. It doesn't always happen, and it isn't so bad that it feels like I got rear-ended, but it's a significant "thunk". This is the only time it ever happens, taking off from a stop normally is smooth and I never get any bangs or anything shifting between gears.
 
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