Makerbot Replicator 2 - Printing fine 10mm, then messes up

[knege]

Hi, we have a couple of Makerbot replcator 2:s at the school where I work.One of them runs fine but the other has a strange problem.The prints are nice the first 10mm (height) or so but then they always get messed up. I have tried swaping to new PLA filament and I have leveled the bed multiple times. The printer is old so maybe some of its parts need replacement?Please let me know if you know whats wrong./Knege

[3DPrinterMan1234]

it could be a z axis loose or bent that's probably my only idea.