From Halopedia, the Halo wiki
Spectre jumping, more commonly known as the "Spectre Hump Jump", is a type of super jump, or super bounce, in which a player will drive a Wuzum-pattern Spectre on top of a Zurdo-pattern Wraith, get on top of the Spectre's cannon and, while continuously crouching, it will rocket them into the air.
This trick works best on a flat surface, such as Headlong. You will need a Wraith and a Spectre. Position the Wraith on the flat surface. Drive the Spectre up the front of the Wraith and when you get out make sure the "U" shaped part of the latch for the Spectre's cockpit is only slightly over the Wraith's back. Next make sure your feet are in the turret while your standing on it and crouch 40-55 times. The higher number the greater the risk of dying. When the desired number is reached, jump and the height that you jump will depend on the number of crouches that you did.