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Pelican Technical Article:

Alternator Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$291 to $519

Talent:

**

Tools:

E10 Torx socket, pry bar, ratchet, sockets: 8mm, 13mm, 16mm

Applicable Models:

Mercedes-Benz R170 (1998-04)

Hot Tip:

Remove the flexible lower air duct for alternator bolt clearance

Performance Gain:

Restores proper battery charge and electrical system functions.
Always disconnect the negative battery cable before doing any electrical work.
Figure 1

Always disconnect the negative battery cable before doing any electrical work.

The belt must be removed from the alternator's pulley.
Figure 2

The belt must be removed from the alternator's pulley. Our 2000 SLK 230 has dual serpentines. The right-side belt's tensioner is close to the fan shroud. An E10 internal Torx socket (green arrow) fits on the adjuster's stud, but there isn't space for a ratchet. We clamped locking pliers on the Torx socket and pulled the makeshift tool counter-clockwise until the belt came loose.

From underneath, remove the lower engine cover (see that article for details).
Figure 3

From underneath, remove the lower engine cover (see that article for details). Then pop the protective boot off the larger electrical connection, labeled B+ on the alternator's plastic cover.

The lower, larger nut (the one with the
Figure 4

The lower, larger nut (the one with the "protection") can be removed with a 13mm socket.

Viewed from the front, the upper nut (D+ terminal) comes off with an 8mm socket.
Figure 5

Viewed from the front, the upper nut (D+ terminal) comes off with an 8mm socket.

Looking straight up, the alternator's two mounting bolts are at about 11:00 and 4:00 in relation to the pulley (green arrows).
Figure 6

Looking straight up, the alternator's two mounting bolts are at about 11:00 and 4:00 in relation to the pulley (green arrows). Their heads take a 16mm socket or wrench. We unclamped the lower air duct and moved it outboard to get the upper bolt out. The lower bolt can be shimmied around the fan shroud.

Theoretically, the alternator should drop down once the bolts are removed.
Figure 7

Theoretically, the alternator should drop down once the bolts are removed. In reality, we used a large screwdriver as a pry bar to slowly push the alternator out of its mounting bracket. The components are aluminum, so whacking them with a hammer isn't recommended. Reverse the removal steps to install the replacement alternator.

R170 SLK alternator replacement is basically a two bolt/two nut job.
Figure 8

R170 SLK alternator replacement is basically a two bolt/two nut job. An E10 Torx socket (arrow) is required for loosening the serpentine belt. Otherwise, basic hand tools and possibly some kind of pry bar are all that's required.

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