After a while my Makerbot Replicator 1 Dual had become unreasonably unreliable. I got frequent air-prints, in fact almost every time.
There is a well known fact that the delrin plunger design Makerbot came up with, is a bad design. After a fair amount of use the plunger gets worn out and does no longer make the tight fit that the filament need to be extruded properly.
On thingiverse there is a spring loaded design that is much better than what i came up with. You can find the design here.
The reason why i made this is that it was faster for me to redesign, rather than order the parts that i needed. I already had a spring and a ballbearing, but they where both oversized and wouldnt fit the already great design made by Torsten aka ivc on thingiverse.
If you want to use my design, keep in mind that it is designed to only use the one extruder (if you have the dual). I have added stl files for both left and right extruder, but the bulkiness of the design only leaves room for one of them to be mounted to the heater block at a time. This was not a problem for me as i never use both extruders at once. For the type of designs i make i never needed dual color objects or different support material than the object itself.
Download files to make this here: