E39iAT transmission

1997 E39 528iAT (BX31513)
Sometimes my automatic transmission behaves a bit strange. It will only happen when I accelerate on a slight uphill road. One out of two things can
happen, ruff gearshift or the transmission takes far to long to decide to shift gear. Usually I help it a long and shift manually, but if I wait long enough it will eventually change. It doesn't happen often, once or twice a month. Should I worry about it? Massive failure in progress?
-- Johan
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Johan Karl Larsen http://www.itlarsen.net
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I don't think BMW auto boxes are bug free. My 740i has a little hazard / race that if you have eased off (~40 - 50mph), and then you press the accelerator again just as the box is shifting up there is something of a hesitation and then a pretty large thump as it re-engages the bands for the gear you were just in either without missing a few beats or (as happened the first time) and I lifted off just as it was changing up having an extended hiccup causing sharp deceleration.

Not a lot.

unlikely.
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It is the opposite of kick down, this is when rpm picks up and gearbox should shift to a higher gear (numberwise), most often from 2nd to 3rd. Even if I ease on the accelerator while rpm is around 4-5000, it won't shift. Tried moving the stick back and forth between automatic and sport mode but it still won't shift. Whenever this happen I must shift manually or wait 10-15 seconds (revs running high) before a higher # gear is engaged.
Heard some talk about a pressure valve or box low on (old) fluid. Comments...
Had a readout an hour ago. Looks like this problem has occurred 17 times altogether since car was new 8 years ago!!! it is getting old :-(
-- Johan
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This is a different fault to what I thought and sounds hydraulic.
1. In normal / economy mode the electronics decide the shifts, and it is odd that they still don't happen.
2. In sport mode the box is AIUI hydraulic, so the change should happen anyway (OTOH the change from say 3rd to 4th or 4th to 5th (depending how many gears you have) may not occur to 90 and not at all going uphill.
It sounds like that there is not enough pressure in the part of the hydraulics that determines the change. Reasons could include: -
low gearbox oil well used (so thin) gearbox oil burnt or contaminated gearbox oil (e.g. from burnt bands resulting from towing) worn pumping mechanism leakage from galleries in the hydraulic change mechanism
if the car is high mileage I should consider having the gearbox oil checked and probably changed.
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