Ive read & searched the forums on this subject. My 73 crank's when cold. But does not crank with key when hot. But will crank right up if jumped across starter with screwdriver when hot. (parking brake set, wheels chocked)
checked small terminal with test light while trying to crank with key in ignition. Light was weak. Acts as if wiring to starter is getting heat soaked. Low Voltage. Maybe ignition switch? Ive seen other articles where someone mentioned having low voltage to the S terminal? What would be that culprit. i do have long tube headers. Wrapped to two tubes closet to starter to see if that might be the problem. Still won't crank over after heating up. Ive also checked the grounds.

 

http://forums.corvetteforum.com/c3-g...art-issue.html

 

Also - make sure the battery is strong and that the alternator is charging it. I also rebuilt my alternator when I found it it was not properly charging the battery, leaving it weak.

 

Old Alaska man. Ive read all of those. But still I'm wondering why I can start my car by jumping across the terminals on starter when hot. But not with the Key. The voltage seems low when checked with a test light. I should get my GM starter in today.

 

I should have said voltage from ignition wire seems low. Battery is new OPTIMA. Altenater is putting out 14 Volt's. Grounds clean

 

With a fully charged battery test each section with a voltmeter to see where the voltage drop is.

 

this will probably start a 'discussion', and I've never proved it myself, except on my own car.....but, there's a 'myth' or 'backyard engineering' idea, that when you turn on your ignition in a cheby car, you dont get full voltage at the starter. And when grounds get cruddy, and cables get full of junk, and your starter gets along in years, that 'not full voltage' gets to the point where it wont spin your engine fast enough to start your car. By jumping at the starter you are bypassing that 'myth' or 'backyard engineering ' idea and giving your starter the full battery voltage. When you bring your starting system back up to 'as new' condition, the issue goes away. According the the 'myth' the same lower voltage now will work fine,
btw GM engineers believe in that 'myth'also

 

Myth maybe? but thats exactly the way my car acts. My thought is this. When you turn the Key you start pulling amps from system the voltage to the wire going to starter cylenoid drop's. Not leaving enough voltage to engage the hot cylenoid. But when you jump it across the starter gets the full 12 volts right now. Which starts the sequence of events inside of the starter. Viola she spins like a top & fires right up. Fresh set of wires & oem starter. Let you know how it goes. Thank's for the input.

 

Not a myth at all.
Everything you mentioned increases resistance and voltage drop.

Even brand new, AC Delco in their manuals recommends continuous cranking for no more than 30 seconds and then allowing 2 minutes to cool down.

 

thankyou noonie, respectfully, bob

 

My understanding is that it is the coil for the starter bendix/solenoid plunger, which when hot, has increased resistance. The current to energize that coil has to travel from the main +12V lead at the battery terminal of the starter, back through the fuse panel main 12V bus, to the ignition switch, back down through the purple ignition wires, to the start terminal on the starter. That's like 8 feet of wire. At 12 ga. Resistance is additive, so add the resistance of those wires to the resistance on the coil. Now the energized field is weak, and the starter solenoid can't plunge the starter gear out, and as a safety, the starter won't spin unless that gear is engaged. So nothing happens.

Check out madelectrical.com for some great explanations. Mark is a savant of sorts, if you ever want to have a couple hour conversation about wiring in 60's American cars, give him a call. Please note that pricing on his website is not up to date.

If you go with a remote starter relay, like I did, and get a cheap foreign made unit from Summit, keep in mind that the terminals may not be labeled. "S" and "I" may be reversed. The instructions mention nothing of this. Ask me how I know.

tbw

 

I havent done it in a real long time, but inside the starter solenoid there used to be a disk, and when it got un-magnettized and carboned up from being arc'd on thousands of times , you could turn it around and start with the fresh side. like I said , its been a real long time.

 

Ding ding ding, we have a winner. GM had a service bulletin on this back in the day. I wrote a complete article and published the said bulletin some time ago in the tech section of VM.

 

i ran a jumper from the starter to a switch that i have just inside the engine compartment. works when real hot...

 

I agree + oldalaskaman's reply. I even remember back in the late 70's when the local Chevy dealer was installing "Ford" solenoids to get heaver gauge wire and the resulting full voltage to the coil in heavy use (hot) vehicles.

 

Those are the really old ones, for a long time the disk has been crimped on, not bolted, so virtually impossible to flip. You can still turn the stud contact.

What you saw were probably real AC Delco parts. What's known as the Ford starter solenoid had a GM comparable known as the
AC Delco "Magnetic Circuit Switch", at least 12 different ones.
Here are 4 of the more common part # if you want to keep your GM all GM
AC Delco # 1114534, 1114537, 1114547, 1115616

 

excellent

 

Excellent troubleshooting! The jumping with a screwdriver from the battery terminal on the top of the solenoid to the "S" terminal proves that the starter, battery, battery cable, and ground cable are good.

As you noted, the problem is that the cranking circuit, which runs from the battery post on the solenoid to the inside of the car, and then to the ignition switch, and then to the neutral safety or clutch switch, and then to the firewall connector, and then to the "S" terminal has too much resistance! Too much resistance will prevent the solenoid from firmly completing its internal circuit to the starter motor itself.

Solution: find out where the resistance is the highest in this circuit and fix it; the highest resistance will be where the voltage drop is the greatest and is, most likely, at a connector! Look for partially melted plastic as a clue. Trace the wires in their entirety! Once I found a fault in a connector hidden under the carpet which joined the neutral safety switch - make sure you check these too.

As a note, heat soaking is often blamed, it's not the real cause, but does exacerbate the problem. In your situation, if the switch, connectors and wires are good and not corroded, you will have no problem with high temperature conditions.