means 45 is configured to fit onto support shaft 43 and be inserted into the trailer reach the expanding friction brake means comprises an air operated resilient diaphragm 46 operated by compressed air supplied from the truck preferably a common resilient diaphragm having a portion opposite each internal side wall of the trailer reach is utilized a central air chamber 48 then serves the common resilient diaphragm the resilient diaphragm is mounted on spool 50 which comprises a cylindrical center portion with substantially normal flanges at each end rings 52 join to spool 50 by means of screws 54 thus clamping the resilient diaphragm therebetween the spool includes a central longitudinal opening dimensioned to fit over the support shaft centering the resilient diaphragm within the trailer reach brake shoes 56 having a planar rectangular portion and inwardly extending tabs on two opposed ends are placed over the diaphragm one adjacent each inner wall of the trailer reach brake linings 58 are bonded on the outer surfaces of the brake shoes to contact the inner walls of the trailer reach when activated the brake shoes do not rigidly attach to any other parts but are freely floating between resilient diaphragm 46 and trailer reach 20 positioning means 60 positions the brake shoes for releasable frictional braking contact with the inner walls of the trailer reach positioning means 60 comprises intermediate spacer rings 62 configured to fit slideably on the support shaft inwardly adjacent the inwardly extending tabs of brake shoes 56 a slight gap is present between the brake shoes and the intermediate spacer rings during normal operation of the expanding friction brake means however the intermediate spacer rings are configured to prevent the brake shoes from contacting spool 50 and damaging the resilient diaphram.