Originally Posted by pbcsd

Have a really old but almost brand new (hardly used) Diamondback Topanga at our cottage equiped with SRAM shifters and Shimano parts.

Have an issue where I can't get the bike to shift onto the larger gear. If I shift and hold the shifter down,the derailleur properly shifts the chain to the larger gear. However,as soon as I let go of the shifter the derailleur loosens and the chain gets pushed back to the smaller gear.

Can't seem to figure how out to fix this issue? Any assistance would be greatly appreciated!