Screw Drive?

[fhhhstix]

They are all custom built other than the Carson which requires modification to get it between the frame rails on a Tamiya truck.

Travis

[Grainfarmer]

Here are some examples (unfotunately in German... , but maybe the pics can halp you):
http://www.modelltruckforum.com/inde...threadID=23553
...or a telescope spindele...
http://www.tmdo.de/gallerie/pic_spi.jpg
http://www.modelltruckforum.com/inde...=9911&pageNo=6 (here you´ll find some pics how it is fixed...)
...also available here:
http://www.racingmodellbau.ch/truckz...-36_38_58.html
The bottom of the spindle is fixed to the chassis, the top end has a joint shaft connection to a geared motor, that is mouted under the dumper.

Hope I could help you with this...