Frank and the lot is absolutely correct. Something to check before jumping into wrenching; is the fluid. pull the stick and smell it. if it smells like gear lube IRS or manual gearbox gear oil, then bust out the spanner and follow the sound advice from Frank and the others. If not, if just smells like a light oil, then its got the wrong transmission fluid in it.
two years ago this was dropped off, with a note "Save me!! There going to take me a part and me to the crusher!
Keys in the ignition. well went down, fired it up. Awesome! it runs!! dropped it into gear, Not so awesome it doesn’t move. lots of bad words… Popped the bonnet pulled the dipstick, Low on fluid, gave it a quick sniff… Hmmm… Dextron (GM fluid here in the states). well that’s not right. put two quarts of ATF (the ford variant) dropped into gear, and a way we went! Yippee quick fix! I like it!!
Hmmm… A bit of slipping up the drive way; more bad words. Let the car sit for a couple weeks, it pissed out some more fluid. Filled it back up with ATF now the car shifts fine. Oddly enough if I drive the car every day it doesn’t leak if I let it sit for more than a week, then it pisses out about a quart.
A bit long winded to say, check the fluid type before you start wrenching. It made a difference to for me. Essentially the Dextron is too thin and the ATF is thicker and I believe what is spec’d as the proper fluid.
XJS well they use General Motors transmissions so Dextron is the proper fluid.
Hope this helps.