Alternator, alternator pulley removal and fan clutch, fan clutch bearing removal on VW Passat TDI

This article shows how to remove the alternator, alternator pulley, or voltage regulator.  Also shown is fan clutch removal and fan clutch bearing removal because you need to remove the fan clutch to remove the alternator.  The bearing is also used on Audi.  

difficulty: 2/5
back to 1000q: B5.5 VW Passat TDI "how to" index

Introduction

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The alternator charges the battery which provides the electrical needs of your car.  The alternator is considered a wear item and should be replaced on an as needed basis only.  Symptoms of a bad alternator would be the battery warning light coming on, less than 14V at the battery when the engine is running, or dimming headlights when the electrical load is higher than normal (and you know the battery is good).  If the battery is weak, engine rpm when starting can be too slow.  The engine computer sees this and does not inject fuel.   Luckily, the TDI has relatively low electrical load since there are no sparkplugs.  The main loads other than the computers are the fuel injectors and daytime running lights.

The most common alternator failure is the alternator pulley.  It has an internal one way clutch.  If the bearings or clutch goes bad, the pulley will spin with the serpentine belt but the alternator shaft will not spin at full speed.  An alternator is designed to provide adequate voltage at low rpm but a bad pulley will cause low charging and a dead battery.  To test it, remove the serpentine belt as described below.  Spin the alternator pulley by hand - you should feel resistance in one direction and none in the other.  Use a wood or plastic pin (to avoid damaging the alternator) to hold the alternator fan inside the alternator and try to spin the pulley by hand - it should move in one direction and not in the other.  If it does, the pulley is bad.

The part that sees the greatest wear are the brushes and copper contacts.  These are the parts that connect the rotating part of the alternator's electricity to the non rotating part of the alternator.  In these 120amp alts, the brushes are held by the voltage regulator.  Since the voltage regulator and brush costs about $95 and a rebuilt alternator costs $110, getting a rebuilt alternator may be faster although the quality of rebuilds can be spotty.  The spec on the voltage regulator states that, at minimum wear, it should have at least 5mm movement.  If the diodes start to go bad that convert the AC to DC you can also lose amperage output and still be at 14V.  The bearings and pulleys also see wear but they should have very long lives if properly tensioned. 

If you are having a charging problem, it's either the alternator or instrument panel light, battery, or grounds.  The battery voltage when the car is off should be over 12V.  The battery voltage when the engine is running should be at least 14V even at idle.  I don't know if it still applies to the mk4 B5 Passats, but the service manual for the mk3 B4 Passats said a bad low voltage warning light in the instrument cluster could cause poor charging of the alternator.  This is not likely since it's an LED so the connector or instrument panel would be more likely.  It could also be a loose battery terminal or ground that prevents proper charging of the battery.  Check for green crusty corrosion on the battery cable terminals.  If you are not sure, take the alternator to an auto parts store because many places will check it for free.  Many places can even check it while it's still on the car.

Parts

120amp Bosch alternator VW# 028 903 031(x indicates rebuilt), from worldimpex
120amp Valeo alternator VW# 028 903 031 a (x indicates rebuilt) 
Note: your original alternator part numbers may be 038903018q or 022903199d so check what's on your car first, from worldimpex

voltage regulator for Bosch VW# 038 903 803 e, from worldimpex
voltage regulator for Valeo VW# 06b 903 803 b, from worldimpex

alternator pulley VW# 022 903 119 d, from worldimpex

fan clutch bearing VW# 058 115 136, from worldimpex, from rmeuropean (made by INA, oem part)

tools for fan clutch removal
    VW tool #3212 or equivalent

tools for pulley removal
    Metalnerd tool MN3400set - serrated alternator pulley bit set OR VW tool# 3310 (socket only)

Procedure

The lower bolt holding the alternator is blocked by the fan clutch so first remove the fan clutch.  Also see 1000q: AC serp belt removal for more details.

Fan clutch pulley removal (lock carrier removed for illustration)

Remove the serpentine belt by loosening the tensioner.  Use a 19mm open wrench on the tensioner tab and rotate the tensioner to loosen it.  

Here is another picture from the front after belt and fan removal showing belt routing.  Belt routing is specific to a TDI.  The plastic fan is held by 4x 5mm allen bolts.

The fan clutch pulley is held with a 8mm allen bolt through the rear access hole.  You must counterhold the pulley to loosen the bolt.  Counterhold the pulley using VW tool #3212 (2 pin spanner wrench pictured in Parts) or equivalent.  I used 2 allen wrenches through the pulley holes as a substitute and a screwdriver to lever them with a strap wrench on the pulley.  Mine was so tight that it bent the allen wrenches so the strap wrench was added.  The pulley is pretty thick but be careful to not crush it with too much force with the strap wrench.

Pictured below is the long 13mm bolt (you can't remove it without removing the fan clutch pulley) and the fan clutch after removal.  As you can see, the lower alternator bolt can't be removed with the fan clutch pulley in place.  This is why you have to remove it before removing the alternator.

The fan clutch pulley then comes right off.  There isn't enough clearance to remove it with the lock carrier in the normal position so just move it to the side.

Fan clutch bearing removal (optional, replace as needed)

The fan clutch bearing sometimes fails, making a gear/howl noise from the front of the car that goes up and down with engine rpm and not road speed.  After removing the fan clutch, spin the bearing to see if it moves smoothly.  If not, remove the alternator/ps bracket, (6x 16mm bolts).  One of the bolts may be blocked by the thermostat flange/plastic coolant hose.  

Use a press to replace the bearing.  Some may use a c-clip to hold the bearing.

Pictured below is the bearing - the 8mm allen bolt goes through it.

Alternator removal

First disconnect the battery.  Place a rag around the negative terminal to prevent accidental contact with the battery.

Remove the serpentine belt and fan clutch as shown above.  

Remove the 13mm nut holding the battery cable, the small plug on the back of the alternator, and loosen the zip tie.

Remove the 2x 13mm bolts holding the alternator and then pry it off.  The bushings are holding it tight.  When you install the new alternator the bushings will clamp it tight again.  Again, you can't get access to the bolts without removing the fan clutch pulley first.

Voltage regulator replacement and inspection

If your alternator just needs a new voltage regulator, remove the 2 nuts (1x 13mm, 1x 15mm) and 1 phillips screw (may vary by Valeo or Bosch part) holding the rear plastic cover.  Remove the 3x phillips screws holding the voltage regulator.  

Remove the voltage regulator.  Measure the length of the carbon brushes (the part that contacts the shaft).  The wear limit is 5mm.  New brushes are 12mm.   If you determine that the voltage regulator is bad but the rest of the alternator is good, replace only the regulator.

Installation

If you are reinstalling your old alternator, the bushings are still in the tightened position - press them out a bit to make it easier to put the alternator on.  A new alternator should have the bushings in the loosened position.

Tighten the alternator bolts to 18 ft-lb.  This tightens the bushings to help hold the alternator.  Then tighten the nuts to 22 ft-lb.  The rest of installation is the reverse of removal.

If you had to remove the serpentine tensioner to get more access, tighten its allen bolts to 18 ft-lb. 

Alternator pulley removal only

Remove the dust cap over the pulley if present.

Insert metalnerd tool MN3400 or VW tool# 3310 socket into the splined hole to counterhold the pulley.  Refer to the pics above.  Then stick the M10 triple square 12 point bit or T50 6 lobe bit through the tool to loosen it.  NOTE: The thread is reversed so turn MN3400 or VW tool# 3310 clockwise to loosen it!

To install, tighten the pulley to 48 ft-lb. 

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