Hi everyone...

2006 525i automatic, 112k miles. I've owned it since new, never driven it in races or anything crazy. With the warmer weather, I've been driving a little more "sporting" that usual lately, but still well within the realm of what this car should be able to handle.

Today I drove to work and everything was just fine. When I left the office in the afternoon to make a ~60 mile drive and as I was driving I noticed that the transmission was shifting rather hard. Sometimes when the transmission shifted (up or down shift) there would be a perceptible "thunk". The car would surge as if power was removed and then suddenly reapplied.

I had no choice but to finish the drive, and then drive the ~60 miles home. So over the course of those two drives, I observed the following:

• This happens shifting between any two gears (not localized to 4-5 or 1-2).
• It varies in intensity between not happening at all, and being such a strong "thunk" and surge that your head actually pops forward and back. The particularly bad ones are often accompanied by a small "squeak" after the thunk.
• Other shifts (could be the very next shift) are as smooth as butter.
• Occurs on upshifts and downshifts.
• It seems to occur more/worse when the engine will be under load after the shift, so it happens more often when downshifting. It also happens if the shift is occurring towards the top of the power band (so still high-ish RPMs after the shift). I think it happens less when the engine will be idling after the shift.
• I've done no service, ever, to the transmission.
• I did try the gas-pedal-reset-adaptive-transmission-trick, to no avail.
• The car will sometimes roll backwards if stopped and I take my foot off the brake. If I tap the gas it will give a small surge and then roll forward as per normal. Prior to this problem it would always roll forward at idle.
• No CEL has appeared or any other warning from the car. I do not own a code tool, though I can go borrow the one from Autozone if it will help.

Any advice from the transmission gods would be helpful. I expect this will be an expensive fix, but I'd prefer not to get totally raped by a shop. I don't have any experience with indy shops near me, as the car has been perfect since I bought it, and once the free maintenance wore off I've been doing my own preventive stuff. Unfortunately, dropping the transmission is beyond my abilities.

Thanks in advance for anything you can tell me!

112,000 miles on tranny with no service -> I'd start there. Other than that, you'd have to get to a tranny repair shop and have them tear it down.

It's my understanding that "lifetime fill/service" means 100,000 miles in BMW talk.

I would replace the fluid first. Look in the DIY section there is a great post there.

maybe an engine issue? how's the trans perform under full throttle?

+1 Fluid and filter. At that mileage I'd expect it's probably a little low. I replaced mine around 60-70k and it was pretty nasty...
It wasn't shifting rough at all but I did notice a lot smoother shifts especially from first to second gear.

location?

Ok well a few things....

It is true that BMW says liftime fill on the tranny and no service required. When you speak to service advisors they will tell you that BMW's lifetime is 100,000 miles. With that said, I still have an E39 in the family going on 324,000 miles and no transmission service...EVER and it had the famous lifetime fill. However, most of us fear our tranny going wrong and do maintenance to the tranny as a preventative maintenance. After all, what kind of super fluid are they using anyway? I personally did fluid/pan/filter swap at 98,000 miles.

What your issue sounds like is possibly a torque converter. http://en.wikipedia.org/wiki/Torque_converter
Now there can be several signs of TC issues but what you describe does sound like it's pointing to that. It appears the TC is engaged mostly but when you hear this 'thud' it's probably because of an engagement which means it had to disengage previously. Keep in mind that torque converter is going to be located about 8" in from where the tranny bolts to the engine which is about right where your gas pedal is. So is this where you're feeling it?

If I were in your shoes I would go to the dealer and pay a diagnostic fee and get the EGS (Tranny) codes if any. You aren't going to get this from a code reader bro. Look at their suggestions and take it at that.
I would service the tranmission but I would wait to pinpoint the issue because the fluid is going to be about $15 a liter and if you DO have to replace the torque converter then you do it all at once. JUST keep in mind that you should probably be very picky who services your tranny. I'm very serious about that...down to every last bolt and drop of fluid.

Fine. No slipping or anything else. I was thinking about it last night and the best analogy I could think of is on a manual transmission car if you are downshifting and pop the clutch out after a shift (rather than release it smoothly)... that sudden application of power and the feeling in the whole car that makes you cringe... that's what it feels like.

Central Virginia

Thanks for the advice and explanation... I've got something to go on now. As for where it's felt - it's really felt through the whole car. The car bucks when it shifts. But I've had clutch plates go in manual cars and that's a situation where it gets progressively worse. But in this case it can shift 5 times in a row cleanly, like the day I bought it, then the next three will be hard, and then it's back to normal. This behavior really has me thinking that it's not a wear issue, it sounds like a fluid pressure issue.

I fully plan to get this sorted out by an expert, but what I was hoping to learn from the Internet were some intelligent questions to ask the shop and pointers for likely problem points so that I can have a chance of knowing if I'm being taken for a full ride.

Follow-up question. The nearest BMW dealership is 60 miles from me. Do you think it's safe to drive it, or should I tow it?

And to think, I almost traded it in on an M5 two weeks ago... before these problems started. :(

Update to this saga:

I had it towed to a reputable indie. I mentioned the ideas given to me here and the owner of the shop agreed that they all sounded plausible and he would check each one out. They put the car up on a lift and immediately saw that the transmission fluid was quite low, suggesting a leak. There were no codes thrown at all, either OBD or BMW-specific. (I checked, and they do have the right computer to read the transmission/engine codes.) I have never seen a puddle of anything under or around the car, and the mechanics couldn't spot any obvious leaks either. So the plan was to refill with fluid, reset all computer bits, and drive it around some to see what happened.

24 hours later I got another call from the mechanic. Repeated test drives after the fluid refill and the problem is still there. Since there are no codes thrown the current mechanic is at a loss. He has a relationship with a Euro transmission specialist, so the car is getting towed to the specialist today. When the specialist was asked over the phone, his gut feeling was the Transmission Control Module and a guesstimate of $3000 to fix.

I will get a more detailed quote and have an opportunity to give a go/no-go on Monday.

*sigh*

Have they tried the "25 second tranny reset"? It's simple, you put the key in and turn to the "on" position (do not turn the car on), then press the throttle pedal for 25s or until you hear some sounds from the transmion. This resets the "learned" shifting from the previous owner, or you, and makes the transmission re-learn the shifting habits for you. This may help you as well.
Still, you DEFINITELY need to find where that leak is, otherwise you will be buying a new tranny at some point. :thumbsup: