Ever since I bought my current S-Type (2005 4.2 NA) the transmission has shifted funny. It jerks into each gear if you are pushing it during a shift and when climbing a hill it seems confused about what gear it wants to be in. How do I know whether it needs a rebuild or just a fluid change? Will the symptoms be much different? Most of the time it acts ok. It has about 117,000 miles on it.

 

The ZF 6HP26 could probably benefit from a fluid change, pan/filter replacement and renewal of the connector seal if that work has never been performed. Most of the time correct shifting returns after this type of service.

 

Do a ZF drain-and-fill first. Many of us have had great success with Mercon SP ATF. If fresh ATF does not rectify your problem, you may want to consider having the ZF 6HP26 Adaptations Drive Cycle performed, assuming you can find a trustworthy dealership still with the necessary hardware and software to perform it....