How to Replace a Car's Starter Motor---Part 2

Saturday morning you give your battery and charging system a full investigation. Even swapping in the new battery from your other car doesn't help. Nope—the screeching has become the only symptom you can elicit. That banshee wail is the teeth on the starter motor's bendix gear clashing against the ring-gear teeth because it's not completely engaged.

The solenoid, or on some starters, just a threaded part of the armature, pushes the bendix gear forward an inch or so until it meshes with the ring gear, allowing the starter motor to spin the engine over until it starts. When the engine rpm exceeds the cranking speed, the bendix automatically retracts, preventing the engine from spinning the starter too fast.

At least that's how it works in theory. Starter motor failure is rarely caused by a blown or shorted motor itself—usually it's a problem with the bendix mechanism or the solenoid. And frankly, most people will never need to replace a starter motor for the life of their vehicle. Intrepid but underfunded Saturday Mechanics might actually dismantle a malfunctioning starter and repair it themselves. You can still find auto parts stores that can get you new bearings, brushes and bendix assemblies. Generally, I just exchange the old starter for a new or remanufactured one, because repairing one doesn't save much money. On the other hand, if you have a rare or hard-to-find starter it might be necessary to fix what you have. Usually, auto electric shops （Denso Starter Supplier) can rebuild or repair a starter with a bad armature, shorted field windings, bad brushes, a bad commutator, or even a bad solenoid if there is no alternative. Be prepared to wait a few days or more.