Atanovich

Greetings,
There is a long stretch of slightly uphill (~2% constant grade) road I often travel at about 55 mph with the cruise engaged. Lately it seems my 2007 530i isn't be able to make a decision whether to use 5th or 6th; it bounces between the two every couple seconds or so. If I go into manumatic the problem predictably goes away. At the least it's annoying and I'm wondering if it indicates a malfunction of the electronics. It never used to do this.

Thx for any insights or advice.

radaddict

How many miles are on the car and has the tranny fluid ever been changed? Any sign of a tranny fluid leak? There is a mechatronics sleeve that is somewhat notorious for leaking (https://5series.net/forums/e60-discu...ailure-135157/).

If no fluid leaks or anything, you can try resetting the adaptations to see if that fixes it (https://5series.net/forums/e60-discu...r-shift-40018/).

ncsugrad2006

Personally I think the "hold down accelerator for 25s trick" is hogwash at best.

If you want to reset adaptations, use INPA to do it right

Agree on the transmission fluid level though--can cause all kinds of things to happen. How many miles on the car/fluid?

radaddict

Well, I don't know that it's hogwash, but I won't cloud this thread with a debate about the acelerator "trick." If the OP doesn't have INPA, he can try it and decide whether it has any merit or not.

ncsugrad2006

I've done it both ways when I had real transmission issues and the 25 second trick didn't change a thing. One reset in INPA and it was night/day difference

Regardless--worth a shot for sure

Redtwin

Is it actually changing gear or could it be the torque converter locking and unlocking causing the RPMs to rise and fall?.

I was speaking to a ZF transmission specialist this week and he said he has seen this issue quite a few times and it was due to TC lock up clutch wear. Quite often the owner will have spent vast sums changing coils and other engine related parts to no avail.

One rebuilt torque converter later and the problem is gone.

radaddict

That was my first thought when I read the OP's post. However, since he said it was bouncing between gears I thought it was more likely a low fluid issue. Of course, low fluid could cause the TC to disengage and then re-engage etc.

I ran into this on a '94 325iS I used to own (with a GM tranny). The interesting and confusing symptom was that RPM would actually drop when increasing throttle (to maintain speed). While cruising along, the TC would disengage resulting in an increase in RPM (up to around 3k on the tach at about 65 MPH). Then when you increased throttle, the TC would re-engage/lock and the RPM would drop even though the car itself was maintaining speed (car would stay at 65 MPH, but the tach would drop to about 2800 RPM).

So, to the OP: If, when you're cruising along with the cruise control on and the car needs to increase throttle to maintain speed (going up hill etc.) you see engine RPM decrease when it feels like it's shifting gears, then your torque converter is losing it's lock and then re-locking when throttle is increased.

So, this is backwards from gears shifting. If the tranny downshifts to 5th gear to maintain speed, RPM will increase. Whereas, if the TC has lost lock and is re-locking, RPM will decrease.

I hope this is not what's going on with your tranny, and, based on your description (and the fact that manually selecting a specific gear alleviates the symptoms) I think it's most likely that you have low fluid.

Atanovich

I appreciate all the great advice. The car has 47k miles on it and the transmission has never been serviced. I'll bring the car to my independent and have them check things out. I previously owned an E39 and there was much debate on whether to replace the "lifetime" fluid. Is that still the case?

ncsugrad2006

last I read "lifetime" had been revised to mean 100K

which is quite sad in my opinion if they really consider that a "lifetime" for a vehicle

Redtwin

Probably because you are not in the business of making and selling new cars.