HiIf you prevent the spring retainer shaft being able to move up and down it will cause excessive pressures on the engine and gearbox
The spring retainer shaft should be free to move up and down to prevent damage and component cracking/failing

Question : do we have to use a split pin or not ?
Thanks in advance for your advice



Another read on Jaguar forums
The split pin through the shaft is to prevent a large bump in the road from dislodging the channel support/center bush

 

in the S type factory service manual it states that the Cotter Pin and a large Washer are to be removed once the transmission is installed.

 

The Mk2 manual gives the same advice. Thinking about it, the pin would be a bit feeble for constraining the enormous weight of an XK engine and gearbox as the car goes over bumps. Also there's the engine stabiliser on the bulkhead that fulfills that function. The idea behind the pin is that for installation it's easier to attach the support channel to the gearbox before jacking everything into position; the pin stops the channel falling off during that process.

 

Thanks to Jose and Peter3442