Bike build advice

[Watercross]

Hi. I recently bought a clapped out GT Outpost (~96) and I’m trying to build it back up (it’s my first attempt).
I’ve installed crankset, rear derailleur and chain. I can manually change gears up (no cables installed yet) but as soon as I release pressure on derailleur, it jumps back down to 3rd gear.
Any advice on how to resolve would be appreciated.

 

[Bike Hoarder]

You need to get some gear cables added, the shifters will 'hold' the derailleur in the right place - once correctly adjusted.

 

[Watercross]

Ah ok perfect - thank you

 

[ishaw]

If with no cables the rear mech is holding in 3rd gear, the limit screw needs adjusting so it sits on the smallest cog. You'll also want to check the other limit screw to stop the chain shifting past the largest cog and dropping the chain between the cog and spokes.

 

[Bike Hoarder]

Good point.

 

[thom04]

@Watercross if you've not already found them, check out the park tool videos on YouTube. They go in to some good detail on derailleur maintenance