Any tips/methods before I give it a try? It's a mates bike and I've never touched Juicy 3s, on my own I'd just pull it apart and see.

pretty simple, pull the old pads out, use a flat headed screw driver to push the pistons back in, and fit the new pads. Im sure i read somewhere that its best to push the pistons back with the old pads still in though..

Have a look at this thread – some good hints. I think 5's are essentially same as 3's. But yes, pushing the pistons in using a flat blade on the old pads definitely helps 😳

Muchos grassy ass everyone, I'll give it a try.

To be honest I think they're a pain in the arse and an example of shite design!

I'm convinced that it is impossible to fit both pads in together alongside the 185mm IS mount. At least, I can never manage it.

I do them one at a time for more room to maneuver – and here's a tip: Tesco clubcard keyring! It's the perfect size. Insert one pad into the caliper pressed against card with the spring in the middle. Then stick the other pad in behind the card. Remove and the spring will be in the correct position.

What didmatt said

Also, ditch the spring/retention clip on the back to make it easy. Put it back on afterward if you want, but unless you've snapped a raised 'knobble' on the pistons off and you haven't killed the spring then you don't need it

If its still a pain, loosen the bolts holding the caliper and adapter together to give you a bit more room. You ought to loosen them off to recentre the caliper after changing the pads anyway (loose claiper bolts, hold lever, retighten caliper bolts, let go of lever, try a few times until its not rubbing)

The only thing I'd say to James above is that the easy way to reset pads is loosen bolts, make sure caliper is free to move, spin wheel and then retighten bolts. This allows the wheel/caliper to find it's own place.

Also watch the pin in the centre of the pistons if pushing them back in without pads.