I was talking to my dad the other day about water crossings and he told me to be uber careful about your speed and gear choice when driving a manual tranny cause once your gearbox and clutch is in water you can't shift because once you step on the clutch water rushes in and completely destroys your clutch. Is this true? Keep in mind he had a run in with this happening when a friend of my dads had to rebuild his Rangers clutch after he went swamping (why he went swamping in a Ranger I have no idea). Can anyone help me out?
I think a lot of this "depends".
Your clutch plate is made from the same material as your brakes. Brakes get wet all the time without failing.
Most clutches are somewhat protected. Even the clutch fork should have a boot around it to prevent anything from getting in, however, on some older and/or modified vehicles, the inspection cover and boot are sometimes missing simply because they weren't put back on, or have fallen off.
If water does get in, if it has mud and sand in it, you can cause damage. Just plain fresh water should be of little consequence, however...
After a day out when a water crossing was involved, you should always inspect all of your fluids. Your Diffs, your transmission, your transfer case, and your engine oil should all be checked for water.