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Old 09-26-2012, 05:47 AM
Stickydonkey Stickydonkey is offline
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Join Date: Mar 2012
Location: Africa
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I've had this acceleration/deceleration hesitation for some time (few months) and been following and reading a few forums about the topic. I see here that some recommend the O2 sensor. I found it to be the fluid in the Transfer Case. Its supposed to be BMW Lifetime fluid (HAHAH). Had mine changed yesterday by a Gearbox (transmission in US) specialist. They replaced the fluid with the proper BMW one (Techron 3?) and reset the "sensors" that measure the viscosity, as read on other forums. This most definitely resolved this for me. The acceleration and deceleration is very smooth.

Whats happening is there are about 6 or 8 clutches in the 4x4 transfer case, always adjusting the traction between 50/50 and 80/20 between front and back. When you pull off, its in 50/50 ratio front/back, and over a certain speed, like maybe 60km/h (2nd gear ?) the ratio starts changing and the various clutches start engaging/disengaging and this is what you feel when they engage or disengage uncleanly. I believe the fluid starts to break down and the viscosity changes and the sensor can only auto calibrate to a certain amount and then there is trouble, which we feel. So, changing the fluid (correct viscosity) and resetting the sensor, the clutches can operate correctly and smoothly again...
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