Is Your Starter Motor Really Bad?By Elina | Published on Dec 03,2015
Before you get all greasy under the car, here are some tips for diagnosing a bad starter:
1. If you twist the key and the dash lights come on dimly, the solenoid buzzes or clicks, or nothing at all happens, it may well be the battery or the cables, not the starter motor. Charge the battery. Your voltmeter should read at least 12.6 volts with no electrical drain on the battery and the charger disconnected for an hour.
2. Check the battery capacity. I use a resistance-type battery load tester. A good, charged-up battery should deliver 150 amps for 15 seconds without dropping below 10.5 volts, and should recover nearly to the aforementioned 12.6 volts within a minute.
3. If the battery checks out okay, look for poor electrical connections to the starter or solenoid, as well as the battery and chassis connections. Accept no more than a 0.5-volt voltage drop between the battery post and the starter hot post. Ditto between the battery negative post and the engine block.
4. Bottom line, there should be 9 to 10 volts at the starter motor hot post when cranking. Don't forget to put the car in neutral or park and block the wheels so you don't run yourself over.
5. Battery cables okay? Try jumping—with jumper cables—directly from the battery positive terminal to the starter motor's solenoid post. If the solenoid pulls in and the starter turns over the engine, you've got a wiring problem.
6. If the solenoid doesn't pull in and energize the armature, try jumping directly to the motor's armature post, bypassing the solenoid. If the armature spins, the problem is in the solenoid or its wiring.
7. Don't forget that some antitheft systems will still disable the starter even if the crooks hot-wire the ignition key. And when something goes wrong with that alarm, you're stranded. It gets worse—it's usually difficult or impossible to disconnect the alarm, in order to keep the car thieves from doing so. Be prepared for serious reading of the factory shop manual or, if your alarm is aftermarket, a return to the alarm installer.
No More Excuses
Regardless, you've determined that the starter is fried. Time to get to it. You might get lucky, especially if you have an FWD vehicle, and be able to swap starters from above the car. If not, the starter usually lives in a really remote location well underneath the car, somewhere near the side of the transmission. Don't try to do this on a hot car—which might seem to be superfluous advice if you can't even get it started—but invariably the exhaust system is nearby, and burns hurt. Also, protective eyewear is de rigueur, because you'll be dropping flakes of rust and underhood dirt from directly above your head into your baby blues. While you're waiting for the car to cool off, chock the wheels and jack it up a foot or so. Ramps will work, but I prefer a pair of sturdy jackstands. On the other hand, I've also been forced to do this in the middle of a muddy field by scooping out a trench to lie in.
Remove the battery ground. Now you can go below and remove the wires to the starter. There will be a fat wire from the battery or, if your car uses one, an external solenoid. There will also be one smaller wire, either a ring lug on a stud or a spade lug, from the ignition key. Older vehicles with points-and-distributor ignition may have a third wire to the coil, bypassing the ballast resistor. Don't get them confused.
Now get a socket and ratchet and probably an extension, and remove the bolts holding the starter to the block. You may also need to remove a heat shield, brace or sheet-metal cover to get everything loose. Don't drop the starter onto your head as the last bolt comes out; it's as heavy as a bowling ball.
Don't get out from under the car just yet. Mark one tooth on the ring gear with some spray paint or even chalk, and inspect every single one of the 140 to 160 teeth by turning the engine over with a big screwdriver for one full revolution. Seriously damaged teeth will require replacement of the flex plate or flywheel, which commences with removing the transmission from the vehicle. Fear of the necessity of this should motivate you to fix a balky-but-still-barely-working starter before it damages the teeth. Labor to remove the transmission and replace the flex plate or flywheel will be 6 to 8 hours, more if you have four-wheel drive. Add in the cost of parts and a ring gear replacement could easily reach a thousand dollars or more.
Take your old starter motor to the auto parts store and exchange it. Don't be surprised if the new starter bears only a faint resemblance to the older one. The industry has been transitioning to smaller, lighter gear-reduction starters that use a higher-speed motor coupled to a planetary gearset to spin your engine faster while using less current. The new starter will have grease already in places where it's needed, so no further lubrication is necessary or desirable.
Replacement of the new starter is straightforward, at least if your vehicle doesn't require shimming the new starter (see page 104). Snug up the mounting bolts, reinstall any braces, covers or heat shields, and hook up the wiring. All you need to do now is reconnect the battery ground, take the vehicle off the stands and start 'er up.
Does My Starter Motor Need Shims?
Some older GM cars may drop a couple of shims in your face when you remove the starter. While most starter motor replacements can simply be bolted on right out of the box, GM engine blocks and starters are dimensionally inconsistent enough to require shimming for proper tooth engagement. Improper tooth engagement leads to a myriad of maladies: The clearance will be too tight or the teeth may not engage fully, giving you gnashing teeth instead of the hummingbird whir of a cranking engine. The best place to start is to replace the shim or shims that came out with the old starter. Don't even bother to hook up the wiring yet. Remove the sheet-metal cover over the bell housing so you can visualize the starter's teeth and the ring gear on the flywheel or flex plate. With a screwdriver, pry the bendix gear forward to engage it with the ring gear. While keeping the gears meshed, measure the gap between the teeth with a 0.032-inch wire gauge. Surprise—there might have been such a gauge included in the new starter's box. If not, a paper clip is pretty close. If the gap is less than 0.032 inch, add a shim. If it's more, remove one. You don't need to remove the starter motor to do this—that's why the shims have a slotted end. Loosen the starter bolt closest to the center of the engine, but remove the other one. The inner bolt will hold the motor up. Now you can slide the new shim in (or the old one out). Reinstall the outer bolt, tighten the inner bolt, and you can recheck the gear engagement.
Occasionally, a starter motor will have proper radial clearance but still exhibit incorrect engagement. It also may be necessary to shim the bendix gear to get full engagement. I'll refer you to the shop manual.