Abstract: The effective length of pump control linkage assembly of a pump-driven vehicle such as a zero-turn lawnmower can be adjusted without directly manipulating a rod or similar member forming the major length of the assembly. The length instead can be adjusted from above with a simple tool such as a screwdriver or wrench using a knob or similar device. In one embodiment, the linkage assembly includes a rod having a top end and a bottom end. The bottom end is attached to the pump. The top end of the rod is received by an internally threaded insert which is housed in a housing. The internally threaded insert includes an engagement structure such as a hex head for mating with the tool. Upon rotation of the insert using the tool, the insert rotates to drive the rod into or out of the insert and, thereby, vary the effective length of the linkage assembly.