Posted by David Sherman on Monday, November 14, 2005 at 11:36PM :
In Reply to: Re: M37 24 volt starter. posted by Robert N on Sunday, November 13, 2005 at 8:35PM :
If it takes 15-20 sec of cranking to start it, after cranking that long, feel all the battery/starter cables, and especially their ends. Any bad connection that's bad enough to reduce the starter voltage will make a cable or connector noticeably warm with that amount of cranking. An alternate version, which sometimes works but is not recommended, is to keep cranking until some connection or cable smokes. That might identify the problem. On the other hand, the starter might smoke first, and become the problem.
If that doesn't identify the problem, I usually troubleshoot these things by using a voltmeter (even a $3 throwaway digital one from harbor freight is fine). Accuracy doesn't matter, but it needs enough resolution to detect the small drops that happen across various connections. Start with the probes directly on the battery posts (not the cable lugs) while somebody cranks the starter. If you don't have a helper, you can wedge a crowbar against the starter pedal mechanism and work it with your third hand while your first two hands are holding the probes on the battery. If the voltage at the battery posts drops 30% or so while cranking, the battery is bad. Charge it at 5 amps for a couple of days, then top off the electrolyte, before you junk the battery.
If the battery voltage doesn't drop much, put the probes on the starter batt terminal and the starter case. The voltage you get there should be within a volt of what you had at the battery posts. If not, work through the system putting the probes across each connection or set of connections, starting with battery negative to chassis ground, until you find some place where there's a significant drop.
Worst-case scenario is that the starter is actually bad (shorted windings will make it both weak and hot) but don't even suspect that until you're sure you have full voltage on its terminals.