rectangular openings 53 fig8 and 12 in a tubular track 54 the track 54 is removably mounted in brackets 56 and 57 on a post 58 having a c shaped cross section which in turn is welded to a side of the frame 10 gussets 59 reinforce the connection between the brackets 56 and 57 and the post 58 a hydraulic cylinder 61 fig1 is pivotally mounted on a pin 62 near the top end of the track 54 the bottom end of a piston rod 63 extending downwardly form the cylinder 61 is connected to a sleeve 64 fig1 and 12 on the pin 51 for moving the carriage 31 vertically on the track 54 as shown in fig8 and 9 such movement of the carriage 31 results in corresponding movement of the frame 10 to change the clearance between the bottom of the frame 10 and the ground the pin 51 extending through the openings 53 in the track 54 limits vertical movement of the carriage 31 on the track 54 steering of the apparatus is effected by the steering assembly indicated generally at 28 in fig8 and 8 referring to fig1 to 18 the steering assembly 28 includes a frame defined by posts 66 on the sides of the frame 10 and a crossbar 67 extending between the posts 66 a tubular spacer 69 with beveled top and bottom ends is connected to the post 66 and carries a pair of brackets 70 plastic plates 72 on the brackets 70 slidably support a rod 73 the outer end of which receives a rod 74 which forms part of a tie assembly 75 the tie assembly 75 includes a two part block 77.