Alternator And Power Steering Replacement Warning

From BMW E34 Encyclopedia

If you are replacing your alternator or power steering lines, you must be extra careful to avoid shortening out the positive alternator wire.

The error is made possible due to the following factors:

Alternator Design Fault[edit]

The thread for the positive wire on your the 140 AMP Bosch alternator always sticks out because it is over an inch long.

The design allows for unintended contact with other metal components in the cramped space. Especially the power steering lines that are due for replacement.

Our recommendation is to unplug your battery during power steering line replacement. You should also secure the wiring on alternator threads with a new bolt (never reuse the old bolt), and use a Dremel to cut-off the unnecessary thread.

Power Steering Line Fault[edit]

The new version of a larger power steering line that runs from the pump to reservoir has a different size bend. The bend is apparent due to a misalignment of the smaller mounting bracket on the power steering line and the engine block.

In my version of the car ('95 production), the alignment of the line was off. I had a hard time routing it without obstructing something.

The most common way people would route this is the same way I routed it (see pictures). This brings the power steering line very close to the thread responsible for securing the positive alternator terminal. Ironically, the plastic 'routing' around alternator's threads made it look like they were made with the line in mind. You are guaranteed to have a fire if the line touches that thread.

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The final revision of the positive alternator cable has a special cover for the threads. Any car before E39 with the M60/62 base engine will have the wires exposed.

We also advise you to coat (after shortening the threads) the top of the bolt with a very thick layer of liquid tape.

Always check the alternator cable at the battery terminal located on the passenger side, near the coolant expansion tank. The cable should be checked for Ohm/continuity against a good, known ground BEFORE the battery is connected.