Yeah, shame nrgserv, would be great but it's a bit of a drive
So, I've had a fun 90 minutes or so...
I took off the cap by undoing the 6 hex bolts. The end cap actually popped off on it's own once undone. Found out this is because the springs in the cap were under load. Picture of cap included below.
Looking into the hub it was just a complete mess of grease. Picture also included below.
Digging around with my finger in all the crap I dug out several bits of metal which were floating free in the goop. Unlikely to be a good sign.
So, I took the rest of the hub off.
I do at least now have a reasonable understanding of how these things are supposed to work. There's a ring in there which slides up and down, pushed by the springs in the cap when locked or unlocked. I assume there are also return springs below the splined ring which push it back up, but couldn't find any evidence of those :S
To cut a long story short, I cleaned the goop out of the hub as much as possible and discovered that the splined ring is totally stuck in the unlocked position. Believe me, I hit this thing with a hammer and it won't budge!
The twist on the cap is in a similar state, no way will it turn.
Both sides are in equally bad state.
I doubt the FWH have worked for years!
There is some good news though. I managed to acost a neighbour to watch the half shaft as I turned the prop and they both turn fine. So, I think this conclusively proves that the FWH are the problem. *crosses fingers*
Interestingly, there was no bolt in the end of the half shaft. There's a hole for one, but nothing there.
So, I think based on my "heavy engineering" approach to trying to get the splined ring to move I can conclude that these FWH are buggered beyond redemption.
I've included a picture of the end of the half shaft below. I'm certain they are 24 spline, but can someone please confirm that for me? Just for the sake of my sanity and my other half not tutting disapprovingly when I buy the wrong bits :S
I'm pretty sure that these are the ones I want:
RTC8163 - FREE WHEEL HUBS 24 SPLINE - Series 3 Parts
Thanks for all the advice, info and encouragement, it's VERY much appreciated!