Re: BF XR6 4spd auto probs...
Is what your auto is doing is whats called flaring, well the transmission is slipping so the engines rpm increases or flares.
The transmission hydraulic system is used for control purposes to accurately predict the achievement of on-coming clutch torque capacity based on a comparison of the modeled volume of supplied fluid to a reference volume representing the actual volume of the on-coming clutch, and in which the reference volume for each type of shift is adaptively adjusted based on input speed aberrations observed during shifting.
If input speed flaring occurs due to an underestimated reference volume, the reference volume is adaptively increased based on the volume of fluid supplied to the on-coming clutch between the initial detection of flaring and a detection of maximum flaring. If the input speed does not flare, but an early pull-down or overlap is detected, the reference volume is adaptively decreased based on the volume of fluid supplied to the on-coming clutch between the initial detection of pull-down or overlap and the expected achievement of on-coming clutch torque capacity.
So basically the transmission underestimates the fluid volume required to change gear, this volume comes from the pressure built up in the transmission from its pump (each gear change has a different amount of pressure to change into the next gear).
If the required pressure is not met, then it flares, so pressure is increased and then there is a violent or sudden gear change. Now with the newer trasmissions they are electronically controlled so its possible its a bad TR/MLP sensor.
My automatic transmission did it on rare occasions but then I did a full transmission service on it (new filter, 12ltr of fluid and flush), now it hasnt done it since.
Changing shift points will not fix this as its an electronic or sensor problem. Sometimes a vehicle fault code can be found and the problem can be fixed, other times its a ghost within the system.
AU1 Forte - 17'' AU2 Tickford rims on all corners, Super low springs,
KYB shock absorbs + camber castor kit and a 3.45 LSD.
Built with spanners, not chopsticks.