87' S15 Jimmy - No Start / No Crank ?

[oscar]

87' GMC S15 Jimmy 2.5
The car has had a no start / no crank ongoing problem for the last 6 months. We first replaced the battery which seemed to fix the problem for about 2 months before returning. We then checked the cable and found the bolt was quite loose at the starter connection we tighten it, started right up. A couple weeks later problem returned. We then tried a screwdriver at starter, started. Today,Got a no crank, with a screwdriver starter engages though no longer wants to catch. I can hear a humming noise coming from the alternator when ignition is at the II position? I'm sure I need a starter, but do I need to replace the alternator as well?

Thanks,
- Oscar C.

[chengny]

Short answer; no. The two components (starter motor and alternator) are independent of each other and separated by the battery.

The alternator charges the battery and the starter drains it. The humming is probably just the diodes that make up the rectifier. Alternators put out AC current that is converted to DC by the rectifier, which is internal.

Pull the starter out. Have someone hold it steady and test it with a pair of jumper cables. Positive/red to the bolt on the solenoid and the negative clamped somewhere on the starter housing (scrape the paint off where you intend to attach the negative clamp).

A good starter will about rip out of your hands when 12 VDC is supplied. Watch that the solenoid drives the pinion gear in the direction of the ring gear on the flywheel.

If it works good that way, I would try to put it back paying close attention to your connections. Also, look closely at the condition of the cables that lead from the battery.

[leolkfrm]

sounds like it's time to rebuild the starter, replace the battery cables, and test the alt after this is done!