the description of the preferred form of the invention will be made in terms of the invention &# 39 ; s application to a lateral slide - out expansion cubicle , or room 2 , in a vehicular trailer 3 or similarly constructed vehicle , however the scope of the invention is limited only by the claims , as properly interpreted . the supporting frame of a typical trailer or vehicle includes a pair of spaced apart longitudinal beams 4 and 5 , interconnected by reinforcing cross members . floor joists 6 of the main trailer area are perpendicular to and supported by the longitudinal beams 4 and 5 . referring to fig3 and 4 , a single one of the supporting frame beams 4 is shown in cross section . to one or both of the frame beams 4 and 5 are attached a pair of spaced apart cantilevered beams 7 and 8 which are perpendicular to the beams 4 and 5 and extend laterally outwardly from the beam 4 . the cantilevered beams 7 and 8 are each constructed from rectangular steel tubing and contain therein telescopically disposed and slidable inner rectangular steel support tubes 9 and 11 respectively . outer leveling assemblies , generally referred to by reference numeral 12 , interconnect the most outwardly , or distal , edge 14 of the extensible area floor 15 with the telescoping floor support tubes 9 and 11 . not having the supporting benefit of the floor joists 6 , the slide - out floor 15 is constructed so as to provide its own support and rigidity . in the partially stored or packed position , as depicted in fig4 the inner portion of the floor 15 is supported by one or more rollers 17 whose axles are attached to the floor joist or an element of the primary floor 20 . the rollers are positioned at the outward edge of the primary floor 20 , so that their axis of rotation is perpendicular to the direction of travel of the floor 15 as it is driven outwardly to its extended position , as shown in fig3 . laterally outwardly of the roller 17 , a sloping aluminum sheet which is rigidly attached to the floor joists 6 forms a threshold 22 which becomes part of the joint 24 between the primary floor 20 and the extensible floor 15 when the extensible floor is in the extended position , as seen in fig3 . to properly mate the inner edge of the extensible floor with the threshold 22 , a molding 26 , comprising an elongated generally triangularly shaped aluminum extrusion , is secured to the edge 27 of the extensible floor 15 . in operation , as the extensible floor is moved outwardly from its stored position over the primary floor and reaches its fully extended position , the inner edge molding 26 of the extensible floor will run over the rollers 17 and slide down the inclined face of the threshold 22 into a provided recess and thereby into the flush position shown in fig3 . when the extensible floor is in its extended position the flat and inclined underside of the molding 26 lies in face to face relationship with the sloped face of the threshold 22 . in addition to forming a suitable junction between the edges of the two floors , the mutually facing sloped surfaces of the molding 26 and the threshold 22 provide a mutual caming action to lift the inner edge of the extensible floor 15 up and out of its recessed flush position when the retracting apparatus pushes the extensible floor inwardly toward the threshold . to make the extended floor level , the outer edge of the floor is depressed through the operation of the two leveling assemblies 12 , which will now be explained . each of the assemblies 12 comprises a vertically oriented flat base plate 30 having an upper inwardly bent flange 32 to which the outward edge of the extensible floor 15 and the outside wall 31 of the room 2 are secured . the lower portion of the base plate 30 carries at each of its lateral edges a &# 34 ; u &# 34 ; shaped channel 34 and 36 . the channels form tracks in which pairs of rollers 41 , 43 and 45 , 47 may travel up and down . the pairs of rollers are supported for rotation by spindles 51 and 53 respectively , which are secured to a mounting plate 55 . the mounting plate is attached by bolts to a mating face plate 57 , which is welded to the outer end of the inner support tube 11 . in the case of the matching assembly 12 , its face plate 57 is welded to the outer end of the inner support tube 9 . an equally acceptable alternative would be to weld the spindles 51 and 53 directly to the face plate 57 and thereby eliminate the need for the mounting plate 55 , which may be provided in some situations for convenience in assembling the leveling apparatus . a stop bar 59 is secured to the top of the channels 34 and 36 to prevent the rollers from coming out of the top end of the channels . a similar stop 61 is provided at the bottom ends of the channels 34 and 36 to prevent the rollers from coming out of the tracks . the stop 61 may be nothing more than a turned in edge of the base plate 30 . although the described embodiment of the invention utilizes a pair of channel tracks with enclosed wheels to provide a sliding coupling between the base plates 30 of the leveling assemblies 12 and the inner support tubes 9 and 11 , other coupling means are deemed to be within the scope of this invention . for example , mechanisms which could be substituted for the wheels and channel tracks include a variety of known guides and slides , such as telescoping members , guide bars within a journal and &# 34 ; v &# 34 ; beds and guides , among others . thus , it is seen that the leveling assemblies 12 provide a vertically adjustable coupling between the extensible floor and the horizontally disposed telescoping support beams wherein the base plate 30 , and the attached floor edge , is free to move up and down , within limits , with respect to the inner support tubes 9 and 11 , thus leveling the floor and making it flush with the surface of the main floor of the trailer . obviously , the weight of the extensible floor and the integral walls , ceiling and furniture within the slide out area , would tend to keep the base plate in its lowermost position , regardless of whether the extensible floor was extended or retracted . since it is desirable that the floor should be level when it is in the packed position , over the main trailer floor , it is necessary that the base plate move upwardly to raise the outer edge of the extensible floor during the retraction , or storing , process . this upward movement of the outer portion of the extensible floor takes place as the result of inward movement of the floor . as the extensible floor moves inwardly , the rollers 17 become a fulcrum and when a sufficient length of the floor has passed inwardly over the rollers , its weight overcomes the weight of that portion of the extensible floor which is outwardly of the rollers , causing the whole extensible floor to pivot so that the inward portion thereof settles into a position of rest , supported by the main trailer floor . it has been found however , that this storing operation can advantageously be assisted by the action of a pair of helical tension springs 65 and 67 . in the embodiment shown , a laterally extending cross bar 70 , welded to the top of the inner support tube 11 , supports the upper end of the helical tension springs 65 and 67 . support brackets 73 and 75 depend from the channels 34 and 36 and secure the bottom ends of the springs 65 and 67 . the two springs provide a biasing force to assist in the raising of the base plate 30 and the attached extensible floor , with respect to the inner support tube position , during the inward movement of the extensible floor . raising the outer floor edge as early in the storage process as possible , with the help of the tension springs is preferred over the alternative of waiting until the floor pivots naturally , due to the magnitude of the inside moment arm . when the extensible floor is pulled from its stored position , that is , slid out to its extended position , as shown in fig3 the weight of the slide - out room , coupled with the increasing moment arm of the extending floor , creates a downward force on the supporting base plate 30 of each of the leveling assemblies 12 sufficient to overcome the closing tension force supplied by the tension springs 65 and 67 . this force pushes the base plates 30 downwardly , permitting the extensible floor 15 to level and be flush with the main floor 20 of the trailer 3 . conversely , when the floor is retracted , the spring forces take over and raise the base plates 30 and the attached floor when the moment arm of the withdrawing unit becomes insufficient to maintain the downward force necessary to overcome the upward tension force of the springs . extension and retraction movement of the slide - out room is procured traditionally . each of the inner support tubes 9 and 11 are provided with a gearing rack 80 along their bottom surfaces . the racks engage pinion gears 82 which are journalled for rotation within mounting brackets 84 secured to the cantilevered beams 5 and 7 . a drive shaft 85 interconnects the two pinion gears 82 . a drive shaft 88 is coupled to the output of an electrical drive motor in a conventional manner . the motor operates to turn the drive shaft and rotate the pinion gears to either extend or retract the inner support tubes 9 and 11 .