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 diagram 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 the 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  the Lucas ACR type, -The regulator is a sealed transistorized unit so it cannot 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 regulator, 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. finally 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 which are soldered in place, so to change the pack the wires must be unsoldered.  If you do want to solder, save money stripping 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 position 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

An 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 feel 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 ring (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 edge 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 the front racket from the rotor assembly (fig 6). With the legs of the puller in place hold on to the rotor 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 washer’s spacers or seals (fig 2).

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

Reassembly is quite straight forward. 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 bearing, 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 barn 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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