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Pelican Technical Article:

Alternator Removal

Kerry Jonsson

Time:

3 hours3 hrs

Tab:

$200

Talent:

****

Tools:

17mm, 19mm sockets with ratchets and extensions, pry bar

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Alternator, battery

Hot Tip:

Disconnect the battery because output lug of alternator will be powered up

Performance Gain:

Replace a bad or noisy alternator

Complementary Modification:

Replace accessory drive belt, also battery if 5 to 7 years old.

The job of the alternator is simple; use the torque of the engine to drive an accessory drive belt. This drive belt also turns the alternator. The alternator can now generate voltage and amperage. Alternators have built in voltage regulators to stabilize the voltage and current supply according to demand and it can do this anywhere from idle to 5000rpm. Keep in mind the alternator is more like a trickle charger than a professional battery charger. An alternator can be rated to put out 150amps but it will take engine horsepower to do it. Alternators are designed to provide just slightly more amperage than required. If an alternator puts out too much amperage it will "cook" the battery which can cause premature battery failure. Excessive heat and escaping Hydrogen gas from the battery vent can be a severe problem. Modern cars like ours also have sophisticated electronics on them and rely on a stable and suitable power supply. Over or under voltage can damage expensive electronics and that can be expensive. In this tech article we will go over all the steps needed to replace your alternator.

In order to remove your alternator you should remove the cooling fan, shroud and you will need to remove your accessory drive belt. See our tech articles on removing the cooling fan, shroud and accessory drive belt. We also strongly recommend you disconnect your battery. There is a wire that runs from the battery to the alternator; if you accidentally ground this wire before disconnecting the battery you can cause serious damage to yourself and the car.

See our tech article on battery removal and disconnect the negative battery lead. You do not have to remove the battery; simply remove the negative terminal from the battery.

Something to keep in mind; your car may have already had a replacement alternator installed and some of the fastener sizes may have changed when that was done. Be prepared if some fasteners sizes have changed.

Working in the trunk, on the passenger side expose the battery and remove the negative battery terminal.
Figure 1

Working in the trunk, on the passenger side expose the battery and remove the negative battery terminal. See our tech article on battery removal. You do not have to remove the battery; you only have to disconnect the battery negative terminal.

You will need to remove the cooling fan to access the mounting fasteners and pull the alternator out of the car.
Figure 2

You will need to remove the cooling fan to access the mounting fasteners and pull the alternator out of the car. See our tech article on removing the cooling fan and shroud.

Remove the accessory drive belt.
Figure 3

Remove the accessory drive belt. See our tech article on removing the accessory drive belt.

Working at the right side of the engine remove the 17mm fastener that is the upper mount for the alternator.
Figure 4

Working at the right side of the engine remove the 17mm fastener that is the upper mount for the alternator.

Pull the fastener all the way out.
Figure 5

Pull the fastener all the way out. You may have to continue threading the bolt out while pulling it because the threads might get caught on the front hole.

At the 4 oÂ'clock position of the alternator remove the 13mm fastener that mounts the bottom of the alternator.
Figure 6

At the 4 oÂ'clock position of the alternator remove the 13mm fastener that mounts the bottom of the alternator. This is also a long bolt so you may have to pull it out while threading it out. You do not have to remove the coolant passage idler pulley to get at this bolt but we have done so for photographic purposes.

The alternator may still be tight in the mounting bracket.
Figure 7

The alternator may still be tight in the mounting bracket. You can use a pointed pry bar here (red arrow) between the alternator and the bracket and pry in the direction of the blue arrow to unseat the alternator.

Move the alternator forward but do not pull to hard since it is still attached by two wires.
Figure 8

Move the alternator forward but do not pull to hard since it is still attached by two wires. You will have to tilt the front of the alternator downward so you have access to the two fasteners that hold on the two wires.

Remove the 8mm fastener (green arrow) that mounts the exciter wire to the alternator.
Figure 9

Remove the 8mm fastener (green arrow) that mounts the exciter wire to the alternator.

Remove the 13mm fastener (green arrow) that mounts the alternator output wire to the battery cable.
Figure 10

Remove the 13mm fastener (green arrow) that mounts the alternator output wire to the battery cable. Remove the cable from the stud.

Pull the alternator up between the engine and the radiator being very careful not to bang up against the radiator.
Figure 11

Pull the alternator up between the engine and the radiator being very careful not to bang up against the radiator. The alternator is relatively heavy and can easily damage the fins. Installing is reverse of removal steps. Position the alternator down in the area of the mounting bracket, attach the small exciter wire, larger alternator output wire to the alternator and tighten the fasteners. Do not over-tighten. Position the alternator in the bracket lining up the mounting bolt holes, installing the fasteners and tightening them. Fit the drive belt and set the tension on the belt. Install the cooling fans and shrouds if you removed them for better access. Start the engine and verify you have proper charging system voltage.

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Comments and Suggestions:
jimdollar Comments: Excellent technical articles with really good photographs, thanks very much, Jim.
January 27, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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