As all auto trans will fail at some point, I think the question should be, "how long in both miles and months was it before the trans failed?" Would it be fair to say if it has been a year and/or 12k miles since the fluid change that changing was not the cause of the failure?

I ignored the advice about not changing and had a very competent indie change all driveline fluids at the 100k when I bought this car. He is a big promoter of changing the fluids even though they say lifetime. It has been about 10k and 10 months and it shifts fine.

Rich

From what I remember, ZF does make similar transmissions for other manufacturers, but each manufacturer uses different electronics, which may also affect the longevity of the trans.

I would have stated it as "contributed to the failure" and not as "the cause of the failure" but yes, I think if it goes a year then the fluid change likely did not contribute directly. It is all opinion, that is just mine.

No flaming. However, if we believed it was the fluid, then the high mileage examples without failures would tend to disprove the theory. Fluid failures don't tend to be random in my experience, they are consequential rather than being the source problem.

A failure related to fluid (whether the fluid caused it, or was damaged by slipping clutches and overheating) involves burnt fluid, and signs of overheating. We don't hear about transmissions being worn out, rather transmissions breaking and not shifting properly. The damage from the ones we have seen is limited to a single clutch pack or actuator, and not pervasive throughout the transmission. A failure caused by fluid would tend to affect all clutch packs. There have been some examples of the ZF transmission having a specific failure of one part (swissfrank has the best post on this) That could be a manufacturing defect, or a design defect, but the failures seem to have additional modes as well other than this specific point.

Driving conditions is an obvious explanation, but the number of examples of pulling large trailers for extended distances tends to negate overloading/overheating as a theory. Extensive manual shifting could be a factor, hard to say.

I come back to the electronics/control package. BMW puts their own controls in these transmissions, to a certain extent. I don't know where the line is drawn between BMW supply and GM/ZF supply, but there is a line. This fits with why the GM and ZF transmissions have similar failure rates. Think about it: what fails randomly on a BMW? Software, sensors, etc, are the most likely cause. When one of those items fails, the affected system stops working, whether it is a clutch pack controlled by a pressure sensor, or a speed sensor, or what have you. Just my theory.

I have to agree with anyone who suggests changing the fluid. Fluid isn't made to last forever. Second and this is the biggest issue is the fluid gets dirty. That's the killer. I went to a BMW dealership today to get parts and starting talking with a tech there. I asked about the "Lifetime" statement for the tranny fluid and he commented that to BMW that was 100,000 miles. He was emphatic that you need to get it changed. Second on most automatic transmissions you have a dipstick and can fill thru that. This allows you to get the correct amount of fluid into the tranny (including whats in the torque converter. My 3.0I doesn't have dipstick. He stated that if you just fill from the torque head bolt on the tranny pan, you won't get all the fluid in that you drained out. Not sure as I have never done this but for those folks who have or those who are BMW technicians is this true? he commented they had a special hose that allows them to get into the trainy to get the correct quantity in there.

Any thoughts?

tranny change
 

I do lots of DYI stuff, but this one I paid a real pro to do. First, a lift is very helpful, then no contamination and my tech's shop I would eat off his floor and I cannot say that about my work area, then there are many types of fluids and you need to make absolutely sure you have the correct stuff and there are tags on the trans to help with this, and then you have to take the temp of the fluid as you fill it, and make sure you change the filter. The $300 I paid was so well worth it to me.
I just got back from a trip out in the huge snow and I had a real gear head interagate me about the car. He wants one too. I had to use the controled decent function again, and it works so well.
Rich
:yikes:

You pump it in from underneath, you don't just fill it to the level plug on the side of the transmission. And, as dipstick notes, you need to monitor the transmission fluid temperature as the level has to be precise, at a certain given fluid temperature. There is a documented procedure in the manual, and probably reproduced on this site if you do a search.

:popcorn: I wish there was a "thanks" button to acknowledge helpful posts, because this is certainly one worthy of it. The transmission fluid change threads are my favorite, with nuanced arguments, well thought out reasoning, and a requirement for application of critical thinking skills. Hadn't ever thought about some of the ideas JCL is writing about and it is also telling that Weasel is skipping transmission fluid changes. Thanks for the efforts. Some of us are listening and deciding.

While I'm assuming the ZF trans is different between the X5 and the 3/5/7 cars, www.e38.org has a couple of nice writeups w/ warming techniques that I used when doing drain & fills on a handful of the 7's that I've done for customers.

I agree, and while maybe I just haven't paid attention enough to the mileages listings on the 6spd, but I've got this impression in the back of my head that the 6spd trannies have had more problems than the 5spd version. Along w/ the survey that started this post, there wasn't any specific mention of which auto tranny they have or haven't changed the fluid on, just adding another spin to this whole thread. Good reading none the less. :)