Sram SX5 to X4?

[bozmandb9]

hi there, I purchased a Marlin AXC Hardtail for my son, and it turns out the rear deraileur is kaput. It's an Sram SX5. Now I've spotted a secondhand X4, including rear mech, shifters, and cassette, it currently has Shimano shifters, and shimano front shifter. Should I get and fit the secondhand stuff, or just replace the rear derallieur?

Thanks guys,

David

 

[Drago]

The SX5 is a decent, if weighty, mech and some of its detail was cribbed by Shimano, which has to be a compliment. What's wrong with it?

 

[bozmandb9]

The adjuster screw which stops it from going into the rear spokes, has nothing to push against, so 1st gear has to be locked out, as does 8th gear. I know nothing about these things, but when we set out on a ride earlier today, it wasn't working at all. Popped into the LBS, and he explained what was wrong, as set it up as above, so at least we could do the ride, but basically a bit has broken off.

Sounds like I'd be best off just replace the SX5 with new.