Does anyone by any chance have tried replacing XJ8 3.5 auto transmission with the transmission from XJ6 type. All I know is there are all ZF6 HP26 but not sure if they are replaceable. Thinking about purchasing a used trans from XJ6 2.7 diesel vehicle and putting on my XJ8. Thank you.

 

AFAIK all the transmissions are the same, but the rear axle ratios may differ so the speeds in each gear match the torque characteristics of the engine. Also the TCM may be programmed differently depending on what engine is in the car.

 

I would imagine that the casing will be different where it attaches to the engine, and that the piston sizes and spring strengths in the Mecatronic unit will be different. (That's the mechanical hydraulic control unit inside the transmission; it also has the electronic control system with it). Whether you can simply change the whole Mecatronic unit and put a 'petrol' one in instead I wouldn't like to say.

 

The bell-housing casting would obviously be different depending on what engine the transmission attaches to, as the HP26 went onto the cars of many manufacturers, Merc, BMW etc as well as Jaguars. The Mechatronic unit may be the same, it may be different and the only way to find out is to ask ZF. I would certainly expect the TCM software to be different. This, of course, can be re-loaded easily. The TCM is inside the box alongside the Mechatronic unit