TROUBLESHOOTING SECTION IX Noisy Operation Noise is usually a very elusive problem, and is generally not the fault of the transmission.  Mechanics should road test  the  vehicle  to  determine  if  the  driver’s  complaint  of noise is actually in the transmission. In  numerous  instances  drivers  have  insisted  noise  was coming  from  the  transmission,  investigations  revealed  it was caused by one of the following conditions: (a) Fan out of balance or blades were bent. (b) Defective vibration dampers. (c) Crankshaft out of balance. (d) Flywheel out of balance. (e) Loose flywheel mounting bolts. (f) Rough engine idle producing rattle in gear train. (g) Clutch assembly out of balance. (h) Loose or broken engine mounts. (I) Power take-off was engaged. (j) Worn universal joints. (k) Driveshaft out of balance. (I) Universal     joint     angles     out     of     plane     or     at excessive angles. (m) Center   bearings   in   driveline   dry,   not   mounted properly. (n) Wheels out of balance. (o) Tire    treads    humming    or    vibrating    at    certain speeds. (p) Air  leaks  on  suction  side  of  induction  system, especially with turbo-chargers. Mechanics  should  try  to  locate  and  eliminate  noise  by means    other    than     a     transmission     removal     or     an overhaul.   However,   if   the   noise   appears   to   be   in   the transmission,    try  to  determine  what  position  the  gear shift  lever  is  in  when  the  noise  occurs.    If  the  noise  is evident    in    only    one    gear    position,    the    problem    is generally  traceable  to  the  operating  gears.    Next,  try  to break the noise down into the following classifications: (a) Growling, humming and grinding.  These noises are  caused  by  worn,  chipped,  rough  or  cracked gears.    As  gears  continue  to  wear,  the  grinding noise  will  be  noticeable,  particularly  in  the  gear position   that   throws   the   greatest   load   on   the worn gear. A  lack  of  lubricant  or  use  of  improper  lubricant can  also  result  in  growling  and  grinding  noises. This  is  because  there  is  insufficient  lubricant  to cool and cover the gears, which allows metal-to- metal contact. (b) Hissing, thumping and bumping.  Hissing noises can  be  caused  by  bad  bearings.    As  bearings wear  and  retainers  start  to  break  up,  etc.,  the noise could change to a thumping or bumping. (c) Gear  whine.    This  is  usually  caused  by  lack  of backlash between mating gears.  Improper PTO shimming is the big offender here. (d) Vibration.      Today’s   improved   highways   mean entire power trains are cruising at higher RPMs. These  higher  speeds  mean  damage  caused  by driveline  vibration  is  more  obvious  than  in  the past. When the maximum RPM of a shaft is reached, it begins to bow.  A resonant hum can be heard, and a vibration will be set up.  This type vibration can  cause  gear  seizures,  broken  synchronizer pins, bearing failures, brinelling and corrosion. During  acceleration  and  deceleration,  the  shaft may  pass  through  half-critical  vibration  (half  the maximum RPM of the shaft).  A whine  or  boom may be heard at this point. (e) Metallic     rattles.          These     noises     within     the transmission   usually   result   from   a   variety   of conditions.        Engine    torsional    vibrations    are transmitted    to    the    transmission    through    the clutch.    In  heavy  duty  equipment,  clutch  discs with vibration dampers are not used, so a rattle- particularly    in    neutral-is    common    with    diesel equipment. In general, engine speeds should be 600 RPM or above    to    eliminate    objectionable    rattles    and vibration  during  the  idle.    A  defective  or  faulty injector would cause a rough or lower idle speed, and possibly a rattle in the transmission.  A rattle can    also    be    caused    by    excessive    backlash between the PTO input gear and the transmission output gear. 25