TC reported Read DT car 'B1' door intermittently isolated in close position. Staff(LVR) checked feed back Rear DT car 'B1" door di not open and close smoothly atLVR and BGS WB. Staff(LVR) unable to isolate the train door  ~~~~~ [Level 3] [NSEWL] T120(3642) train doors not proven closed CTH WB : TC reported TIMS showed B1 train doors in car 3641 were slow in closing since ALJ WB. Staff(LVR) checked & f/b doors were jerky during opening & closing. Staff f/b faulty doors were unable to be isolated in closed position. L3 3641 B1 door performed the following checks : Fault code: 933 (Saloon door B1 operation timeout), 936 (Saloon              door B1 Door open in motion) ER & Fault Trace: TIMS showed 3641 B1 door close operation                         timeout once and subsequently, multiple fault                    codes of Door Open in Motion. ER showed TC                       cycled doors 7 times while station staff                         attempted to isolate the door 9 times. Fault                     trace showed that the door was not able to                       close fully and the door was stuck at a gap of                   56mm and not able close any further. Train                       returned to depot with doors not fully closed.                   Found door isolation assembly faulty. FOD found: N Weather strip condition ok: Y Checked roller condition ok: N, found RHS outer roller delam &                                LHS outer roller pitted    Clean J-rail & guide rail: Y Push/pull door smooth & no wobble: Y, after rectification Door cyclic test 20x, DIR extinguish ok: Y, after rectification TIMS door static timing test pass: Y, after rectification Door lock switch red line flush with surface for positive latching: Y Door close switch actuating plate distance ok: Y Door gap (criteria 63mm+1.5mm): 63.6mm Replaced 3641 B1 both LHS and RHS to iron rollers. Replaced faulty door isolation assembly. Function test - ok.  Sarma/Alan/Lee PT 45291 #3641 B1 Door Isilation Assembly S/N : OLD : C151BIL157630 NEW : C151BIL157030