Motor car Guide to Classic Car alternator sevice & overhaul

Replace Internal Brushes

Except  for the  Lucas  ACR series, most  alternators with internal brushes are difficult  to dismantle  and  can only be repaired by an auto electrician. On  ACR  types, use  a socket spanner to undo  the two recessed bolts which hold  the black slip  ring cover  (fig 1). Make  a note  or draw a diaorarn of the wiring (fig 2)  and then disconnect  the  connection from the brush holder to the diode pack. 

1 Undoing the slip ring cover	2 Types of voltage regulator connections

Then undo the  screws  which  hold   the  brush  holder and  the surge  diode to  the alternator  casing  (fig 3) - some ACR models also have a screw holding the voltage regulator to the casing - and  lift the  brush holder away  (fig 4). Undo the small  bolts  holding the bushes  to the brush holder making a note  of the positions of the wires to the regulator (fig 2). pull  the brushes out of the holder (fig 5)  

3 Unscrew the alternator brush holder	4 Lift away the brush holder

The brush nearest  the  centre should have a small  flat  spring fitted  along- side  it. Check  the length of the brushes (fig  6) and if they are less than 3/16  in. (5 mm) in length buy some  new  ones. Clean  the holder with  meths and  then  fit the new brushes into place remembering to fit the flat spring suppled with the brushes  (fig 7). replace thel small bolts  that hold the brushes. together with any wires  that  were under them Now reassemble the unit.

5 Pulling out the brushes	6 compare new & old brushes	7 Rember the spring

Change a ACR voltage regulator

The only  alternator with  an internal  regulator  which can be easily  dismantled  IS  the Lucas ACR type, -The  regulator is a sealed  transistorized  unit  so  it can not  be   repaired   if it  is faulty you  will need  a new one, There  are  several  different types  of regulator and   it is best to take  the  old  one  to  your dealer to make   sure   you  get  the right  one, If the  original  type of regulator  is  not  available your dealer will be  able   to  offer   an alternative type   which   will fit, To remove  the  requlator,  first undo the slip  ring cover and  find   the  regulator screws  Some  models    have   two screw  one to the  alternator body and one  to the  brush holder (fig  1) -  others  are held by  one screw on  to the brush holder (fig I), Draw  a diagram  of the regulator connections  and  then remove them.  Undo  the  screws  and  lift the regulator  away,  Fit the new regulator into place  and reconnect  all the  leads. finaly  refit the slip ring cover.

Voltage regulator fixings

Renew the acr slip ring

Check   the  surface   of  the  slip ring  for  glazing  or wear.  If the copper   surface  of the slip  ring looks  dull   -   as if  coated   with varnish   -  you  should  clean  it with abrasive paper.  Take  care not to allow  grit  or  dust  to fall inside     the    unit.    When  the copper   slip  ring  is smooth  and bright  give  it  a wipe  with  a rag soaked  in meths. If the slip  ring  IS  badly  worn, scored   or  holed   it  should   be replaced   as it  will  wear  out the brushes  very  quickly.   With  the brush   holder    removed,    undo the  three  bolts  which  hold  the front   and  rear   casings   of  the alternator  together  (fig  1). Carefully   pull  the two brackets apart  -   the  rotor  and  slip  ring come  off with  the front  bracket and  the  diode   pack  and  stator windings   come off with the rear bracket. Support   the  alternator    firmly and then  unsolder  the two wires on the side  of the slip ring (fig 2). If you do not want to do this part of the  job,  strip  the  alternator yourself   and  take   it to an  auto electrician   to have  the soldering done.  These  are firmly attached so  you  may  have   to apply   the soldering     iron   for  some   time before   the solder   starts  to melt. The  slip ring  will heat  up while unsoldering    so use  a rag  to pull it off the top of the rotor shaft,  or you may  burn  yourself. Push  the  new  slip  ring  on  to the  rotor  shaft  making  sure  that the  small  spring  clip is in place and  that  the  pip  inside   the  slip ring  hole  locates   in the  groove on  the end of the  rotor   shaft. Solder     the    wires     into   their grooves   on the  slip  ring  but  do not use  too much  solder on the join -  'it may  foul on the  diode pack  when  you reassemble  the alternator. When  reassembling  the  unit make  sure  the  ventilation   slots in the  slip  ring  cover   are  clear and then  refit it to the alternator. Now refit the unit

1 Removing the alternator through bolts	2 The 2 wires that need to be unsoldered

Renew the ACR Diode pack

The diode  pack,  or rectifier, is, bolted to the rear  bracket   of the alternator.  It is connected to the windings   by three wires wich are  soldered   in place,  so to change   the  pack   the  wires must  be  unsoldered.  If you  do want to solder,   save  money strippinq   the  unit  yourself d  then   taking it  to an  auto electrician to have the soldering done  Make  a note of where  the three wires  go (fig  1) and  then unsolder each  one -   use', a pair of long-nosed   pliers  to grip  the Wire as close  to the diode  pack as possible.Apply the soldering  iron to the terminals for a few seconds   until the wire  comes  loose and quickly pull  the  wire  outwards away  from the terminal. With all three  wires  removed undo  the  nut holding  the  diode pack  to  the   alternator  (fig  1). Some types  are  also held  inside the  casing  by  an extra  nut and racket, so remove  this, if fitted. As you lift the pack  out notice the   position  of the washers   and the  small.  black rubber cap. These  must  be   transferred  to the new  pack  before  fitting it. place the new diode  pack  into pcsition  and  tighten up the securing  nut. Fit the three  wires to their   terminals,  and  solder them into position.  Do not keep the soldering  iron on  the terminal  for  more than a  few seconds at a time the  diode pack has  delicate components that are  easily  damaged.  Again, use the long-nosed pliers  to grip the wires as this will help conduct  the heat  away.

Diode Pack Held in by a nut it has 3 wires

Check the bearings for wear

A alternator which  is noisy  in operation usually  has  worn bearings. If  the  noise  is only slight then it is probably not worth doing  anything  about,  but  a  loud  rattling or  'graunching' nose  should  not be  ignored. To check the front bearing  for wear hold  the  alternator  firmly and  spin  the pulley  - it should rotate smoothly, any roughness or grinding  noise means that the bearing  is worn. Also try to rock the pulley  from side to side (fig 1) -  very slight movement   is acceptable, so long as  the bearing  does not sound rough but if the play is more than 1/16 in,  (1,5 mm)  then  the  bearing must be replaced  The rear bearing is  more difficult  to check  as the alternator  casings  have to be separated  (see Step 4) to get at it. Once you have separated the alternator casings, check the bearing  by spinning it. It should not feol rough or make a grinding noise  In practice  the rear bearing  seldom wears as it .has very  little  load, unlike  the front bearing  and is well  protected from dirt  by the alternator casing,

Test Front bearing play on a car alternator

Remove The Rotor

The   rotor   has   to  be   removed before  the  front  bearing  can  be changed. To remove it, hold  the rotor  tightly and undo the  nut on the end  of the shaft (fig  1). This is often very tight use rags or wear a pair  of rubber gloves  to get some  extra  grip.  Take  off the spring  washer  and  put  it safely to' one  side. Using  two  flat-bladed  screwdrivers 

1 Undoing the rotar nut	2 Lever of pulley

  lever  the pulley off the shaft  (fig 2). If it is tight  do not be tempted   to use  a lot of force  you  may crack or bend  the pulley. if it will  not  budge  you will have to use  a puller on it, Once  the  pulley is off you  can remove the  cooling   fan.  Rotate the  fan until the  cut-out  slot lines up  with  the  Woodruff  key and then pull it off.  Use a pair of pliers to remove  the  Woodruff  key  if  it  is  stuck, carefully prise  it out  with  a  screwdriver (fig  3) -  and  put  it somewhere safe.  Take off the spacer rinq (fig 4) which  holds  the  fan clear of the  front  bracket  and   put  it safely

3 Prising out woodruff key	4 Dont forget this spacer

with the  Woodruff   key. Position the  front  bracket  on the  edqe   of  a  sturdy   table  or workbench Make  sure  the rotor is not fouling  on the edge of the  bench and  then  put   the pully nut back  on the end  of the shaft ,  With  a  copper  or  hide- headed   mallet   drive   the rotor out of the front bracket  (fig  5). If the rotor  shows  no sign  of moving do  not  carry on  hitting the end of the shaft  -  all you will do is  damage  the nut  and the threads.   Instead use  a two-  or three legged  puller   on the  end of the  shaft  to'  pull thefront racket from  the rotor assemby  (fig  6). With the  legs of the  puller in place  hold on  to therotor and tighten up the  nuts  or  bolts  on the  puller, making  sure  it does not slip off.

5 Tap rotor out with mallet	6 using a Puller on front alternator bracket

Renew The Front Bearing

The front bearing  in  an  alternator is a ball bearing race very similar  to the ones  used  in dynamos. These  are sealed-for- life   units    so   once    dirt    has entered   the bearing  it will wear out quickly. Apart  from an over- tightened  drive   belt,  the  main cause of bearing  failure  is dirt getting  past  a damaged  seal. The  bearing is  held  in by  a circlip  which locates  in a groove in the  front bracket.  Hold a rag over  the circlip  and  prise  it out with  a long,  flat-bladed  screw driver  (fig  1). Do this  carefully a's the circlip  is very  springy.With  the  circlip  removed the bearing is simply  pushed out If  it   sticks use a  socket  and hammer .to  tap  it out. Make  a note of the  position  of washers  spacers   or seals  (fig 2).

1 Prising out the circlip with a screwdriver	2 New bearing with spacers washers & seals

Reassembly  is quite  straight frorward.  Fit the  new  seal  and bearing   into  the  front  bracket, gently tapping  them into place  if necessary. Once  the bearing   is properly  seated   push  the circlip back  into its groove  with two screwdrivers.    This requires patience  as it is a fiddly job but it will go in eventually. Refit the  bracket    to the  rotor by  tapping  the front  bracket with a soft-headed  mallet.  Alternatively,  use a  press   to fit the rotor into the bracket.

Renew The Rear Bearing

To change the rear bearinq, separate   the two casings of the alternator  and remove  the  slip ring  Then using two screwdrivers  carefully try to lever the bearing off the  rotor shaft (fig 1).  If  it is very  tight you will have  to use a bearing   puller to remove  it or have  it removed by an  auto electrician. Fit the new bearrnq by  tapping  it into place   on the  rotor  shaft  using  a socket  as a drift (fig 2). Refit the slip  ring  and  reassemble the alternator

1 Lever of bearing with screwdriver	2 tapping on the new bearing

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