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Pelican Technical Article:

Alternator Replacement

Mike Holloway

Time:

1 hour1 hr

Tab:

$100 to $400

Talent:

*

Tools:

8mm Allen, 13mm Ratchet Wrench, 17mm Wrench

Applicable Models:

Mercedes-Benz R107 (1972-89)

Parts Required:

New Alternator

Hot Tip:

Replace worn belts

Performance Gain:

Reduced Electrical Issues and Battery Drain

Complementary Modification:

Replace Air Pump Belt, Air Conditioner Belt

The alternator charges the battery and provides your car with a constant source of electricity while the engine is running. Over time, the alternator will begin to fail and cause trouble with the various electrical devices in the car. If you suspect alternator trouble, you need to check to see that is operating correctly, and is indeed the cause of the problems with your charging system. Sometimes bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

The first thing to check is the battery light on the instrument cluster. This light bulb is part of the alternator field circuit; if it burns out the alternator will not charge. Simply turn the key on and see if it illuminates briefly then goes off. If the light does not illuminate, you'll need to replace it before continuing.

Inspect the belt that drives the alternator. Is it tight and amply turning the alternator? If not, then check the condition of the belt, they seldom break, but they get brittle and glazed with age, and can slip on their pulleys. Replace the belt with a new one as required.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. Wait two minutes after starting the vehicle for (accessory cycling) voltage to stabilize. When the car is running, the voltage must read in the range of 13 to 14.5 volts with the engine at 3000 rpm. If your battery appears to be leaking, then your voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 15.5 volts when the engine is running, then the regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help to neutralize the acid considerably, and prevent it from eating the metal.

An important item to check on your car is the engine ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the engine ground strap is damaged or disconnected, you will have problems, including electrical system malfunctions, no and/or difficult starter cranking.

If you've checked all of these things and you still have charging problems, it's likely the alternator will need to be replaced. The first step in replacing any alternator is to disconnect the battery. You will be working around live electric wires here. If you happen to touch the lead going to the alternator against something, you can cause permanent damage to the electrical system if the battery is hooked up and give yourself a heck of a shock.

If you are replacing the alternator it may be good idea to install a new belt as well. If you choose to do that you must also remove the air pump belt and air conditioner belt. Inspect the alternator belt for cracks signs of wear.

With the other two belts removed, you need to loosen the 17mm bolt attaching the alternator to the solid mount. There is a nut and bolt that attaches the alternator to the arm bracket. This bolt has the tensioner teeth built into it like the other accessories. You need to use a 17mm socket and loosen the nut on the back of the alternator. With this loose, you can use your 17mm wrench on the front bolt to take the tension off the belt. Remove the belt and use a 13mm wrench to remove the upper bracket from the solid mount. This will give you more room to remove the alternator and get access to the electrical connections at the rear.

If you are just replacing the voltage regulator you can simply turn the alternator over, use a Philips-head screwdriver to remove the old one and install a new one.

If you are replacing the alternator remove the two electrical connectors using an 8mm and 13mm wrench.

Begin by removing the ground cable from the battery and making sure it cannot accidentally come in contact with it while working.
Figure 1

Begin by removing the ground cable from the battery and making sure it cannot accidentally come in contact with it while working.

Loosen the 8mm Allen bolt attaching the alternator to the solid mount.
Figure 2

Loosen the 8mm Allen bolt attaching the alternator to the solid mount.

There is a nut and bolt that attaches the alternator to the arm bracket.
Figure 3

There is a nut and bolt that attaches the alternator to the arm bracket. This bolt has the tensioner teeth built into it like the other accessories. Loosen this with the 13mm socket wrench. This will allow the belt to slacken.

Loosen the nut on the back of the alternator with a 17mm wrench.
Figure 4

Loosen the nut on the back of the alternator with a 17mm wrench.

Loosen the front 17mm bolt where the ratchet tensioner is.
Figure 5

Loosen the front 17mm bolt where the ratchet tensioner is. This will loosen the belt.

Remove the 13mm bolt from the bracket by taking off the nut in the back and pulling the bolt through the bracket.
Figure 6

Remove the 13mm bolt from the bracket by taking off the nut in the back and pulling the bolt through the bracket.  

Once the alternator is free from the bracket and belt, turn it over and disconnect the electrical connector.
Figure 7

Once the alternator is free from the bracket and belt, turn it over and disconnect the electrical connector.

If you are only looking to replace the voltage regulator, use a Philips head screw driver to remove the old one and install a new one.
Figure 8

If you are only looking to replace the voltage regulator, use a Philips head screw driver to remove the old one and install a new one.

Once the voltage regulator is removed, you should inspect it for any corrosion.
Figure 9

Once the voltage regulator is removed, you should inspect it for any corrosion. Installation steps for the voltage regulator as well as the alternator are the opposite of removal.

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