1972 does not turn over when hot

[scottb5y]

Hi,

My 1972 will not turn over after being driven for 20 minutes or so. I'm pretty sure it's a bad set of contacts or something like that in the ignition switch, but wanted to see if there were other things to consider between the key and the starter. Meaning is there a relay in there somewhere I don't know about ?

I know it's not the starter because when this first happened, I wanted to rule out the start/solenoid. So I ran a set of jumpers (1 from the solenoid and 1 from the start main lug) up to the fenderwell and capped them off. Now when it gets hot and fails to turn over, I pop the hood and just jump it. It works, but a bit of a hassle and not very easy for tohers to drive my vehicle (good excuse I guess).

It's the original switch so my guess is it's worn out and something in it does not like the heat.

Are there other things I should check first ?

[seamus2154]

I know we forget but our vehicles are 42 years old. If it is starting when you jump it the only thing you are cutting out of the equasion is the wiring, ignition switch, and key??? I would replace the ignition switch and check all the wiring from the starter back to the key. I have seen some starters not to work when hot because the solenoid needed shielding, but if it starts when you jump it I guess that rules that out. I don't know of a relay for the starter maybe someone can chime in.

[leftybass209]

I think you pretty much narrowed it down. If the only variable to the equation is heat, then the switch could be the case. how does your wiring look, and does it feel brittle? Are there any splices or jumpers along the wiring? You can first check the switch by cleaning the contacts with a brass wire brush if they are visibly corroded. That's not to say something isn't wrong inside of it though.

[geezer#99]

Could be several things.
Too much advance, corroded wires, bad grounds but not likely the ign switch.
Check your timing.
Clean your grounds.
And then wire in a remote solenoid. It's likely heat soak on the starter/solenoid.
Here's a link on how to set it up.
http://www.oldengine.org/unfaq/solenoid.htm

[72_swb]

You should jump the constant hot and the purple wire off the back of the key switch. That away if it works when you do that you know its the switch or not. The back of the switch should say sol (solenoid) on the back of it.

[rexrandom]

+1 on the Ford solenoid. Esp for headers...

[scottb5y]

The to everyone for their replies. I'll dig into the switch as suspected. Wiring is a good call and agreed it does need to be replaced. Thx to 72_swb for the details on jumping the switch

[seamus2154]

hh

[WIDESIDE72]

Imo it sounds like a classic case of chevy starter solenoid heat soak. I am going to guess the truck in question has headers. You can try a heat shield or wrap, but will probably have to do the ford type remote solenoid mod.

Just curious why everyone thinks its the igntion switch. Something im missing? How do conditions under the dash change when the engine gets hot?

[hugger6933]

sounds like heat soak and headers to me to.

[72_swb]

Originally Posted by WIDESIDE72

Imo it sounds like a classic case of chevy starter solenoid heat soak. I am going to guess the truck in question has headers. You can try a heat shield or wrap, but will probably have to do the ford type remote solenoid mod.

Just curious why everyone thinks its the igntion switch. Something im missing? How do conditions under the dash change when the engine gets hot?

Im not the best mechanic here by all means. But if he applies power to the soleniod and it cranks right up after the motors hot, then the soleniod is still working. I may be missing something also. But I have seen ignition switchs go bad. I beleive the ignition switch carrys an electrical load threw it when the key is on. So it could be heating up and loosing contact. But bypassing the switch under the dash would be a quick test. He already ruled out the soleniod by jumping it with a hot wire while it was hot.

[franken]

Doesn't turn over is unclear.
If the solenoid clicks, or nothing happens, it could be a solenoid problem.
If the starter turns slowly, its probably not the solenoid.

Let's think about what's happening...
The ignition switch turns on the solenoid, which (is an electric switch that) turns on the starter motor.

If nothing happens or the solenoid clicks, and that's all, it may be a problem with getting enough current from the battery all the way to the solenoid.

Check the big ground cable by jumping from the neg batt post to the starter case w/ one side of jumper cables and test by starting or trying to. We like the ground to go to the engine rather than something bolted to it. A good spot is the holes at the front of the engine below the water pump that were once for motor mounts.

Another test is to feel the cable ends for heat after cranking for a bit when cold. Resistive connections will get hot.

Then there are all the positive side connections from the smaller wire coming off the battery all the way to when it goes through the ignition switch (turns purple) NSS and on to the solenoid. All those connections should be clean, and not get hot after cranking when cold.

A Ford solenoid won't help a slow starter, unless its a wiring issue that was fixed accidentally by wiring the solenoid in, or if the lugs and disk in the solenoid are burned. In that case the extra solenoid was a waste.

The point is, a Ford solenoid is an added complexity that will usually not be needed if the problem is approached methodically. Its also something that has to be troubleshot next time there's a cranking problem.

Troubleshoot or throw parts at the problem...

[FRANKENSTEINC10]

mine was doing the same thing.next time instead of jumping it to start it just bump it and the try the key. my ignition was not working and I would bump the starter over and flip the key and it would work! changed ignition switch. work perfect

[67 chevelle]

Originally Posted by geezer#99

Could be several things.
Too much advance, corroded wires, bad grounds but not likely the ign switch.
Check your timing.
Clean your grounds.
And then wire in a remote solenoid. It's likely heat soak on the starter/solenoid.
Here's a link on how to set it up.
http://www.oldengine.org/unfaq/solenoid.htm

Agreeded , does your truck have headers , if yes then I defiantly agree , ford relay has fixed this issue for me

[scottb5y]

Hi,

Thx for everyone's replies. It's been a while, but I'm posting to close this out as the issue was finally resolved and I hope this might help someone out down the road. As it turns out, I think Franken above was closest with his diagnosis / troubleshooting suggestions.

The problem turned out to be a bad ground in the starting circuit. When the engine was installed, they grounded the battery negative to the frame. So my guess is when it was cold and less resistance, it would start. As it heated up, and resistance increased, it would not. At any rate, running the negative of the battery directly to a cylinder head and the frame solved it.

The longer version of this story is step 1 was to replace the ignition switch. I pulled it and it came apart in many pieces with broken metal tabs, etc. It was badly burned from arcing, so while it did not end up being the core problem, it contributed and needed to be replaced.

Since the problem continued, I finally had some focused time and with the help of a wiring diagram and my old "Automotive Electrical Systems" book, I realized it had to be bad ground. The ultimate hint was when trying to start the vehicle by jumping across the starter and solenoid with the key in the off position, a spark would jump across the transmission linkage to the frame.

Hard learned lesson, but I won.

Thx for everyone's help !

[hdff]

Originally Posted by 67 chevelle

Agreeded , does your truck have headers , if yes then I defiantly agree , ford relay has fixed this issue for me

Can someone explain the ford fix to me please. I have had the same problem and I have headers. Turned the key heard nothing got out to look and try some more. The only thing I noticed was the hot wire from the battery was hot. After maybe 15 minutes it started

[BLK96]

Ford fender mount solenoid from 70's-80's. The + battery cable gets moved from starter to input term of solenoid. Will need shorter cable. Run another cable from output term on solenoid to orig. location on starter. Remove smaller wire from starter, it now gets re-routed to "s" term on Ford solenoid. Finally, use a small piece of heavy guage copper wire (romex ground works well) and connect between battery terminal on starter and smaller start terminal on starter (where smaller wire was previously). I mounted Ford solenoid where junction block was on passenger inner fender. This modification allows full voltage to starter solenoid, virtually eliminating voltage drop in smaller start wire due to heat, age or whatever. I also like the fact the heavy batt cable is not "live" anymore, only when starting. If the Ford solenoid has a small "I" terminal in addition to the "S", it isn't used.

[RichardJ]

Ford solenoids are over-kill, ugly and have the large posts hanging out in the open waiting for you to drop a wrench on them.
The Ford starter solenoids in some cases can handle as much as 300 Amps and may require as much as 5 Amps to energize.

The small Bosch type relays require less than 50 milliAmps to energize and many can handle 30 to 40 Amps.

I get mine from the wrecking yard. On GM cars from the mid '80s, up through the '90s you can find as many as ten on a single car. I pick the ones that have two or three 12 or 10 gauge wired to them and I know they are at least 30 Amps. Get the relay, plug and as much wire you might need. Usually a couple of bucks each and they have a low failure rate.
Get matching relay types and use a bank of them for fans ,headlights, AC or whatever.

[aris_unlimited]

Do you have headers on it? Or is the engine radiating more heat than it would have stock for some reason? I had the same issue on a camaro turned out the starter was susceptible to heat sink and wouldn't work when hot.

[MARKDTN]

Originally Posted by RichardJ

Ford solenoids are over-kill, ugly and have the large posts hanging out in the open waiting for you to drop a wrench on them.
The Ford starter solenoids in some cases can handle as much as 300 Amps and may require as much as 5 Amps to energize.

The small Bosch type relays require less than 50 milliAmps to energize and many can handle 30 to 40 Amps.

I get mine from the wrecking yard. On GM cars from the mid '80s, up through the '90s you can find as many as ten on a single car. I pick the ones that have two or three 12 or 10 gauge wired to them and I know they are at least 30 Amps. Get the relay, plug and as much wire you might need. Usually a couple of bucks each and they have a low failure rate.
Get matching relay types and use a bank of them for fans ,headlights, AC or whatever.

I don't think you read that correctly. You can't use a Bosch style relay for this fix. You are basically doing what Ford did on some 429/460s by using a remote solenoid on a Delco starter (look at PH140-006 http://bpi.ebasicpower.com/search2/s...?q=pcm+starter). You are moving the solenoid so that battery power and activation (purple wire) goes to it and then when it is energized you have full battery power on both the big lug and the "S" lug. The solenoid on the Delco starter still works, it just doesn't have to rely on the long length of purple wire to get power, it has a short piece of wire from the main lug to the "S" terminal (Ford used a metal plate when they did this-see post #2 http://www.hotrodders.com/forum/ford...er-201783.html also see post #15 for a circuit diagram).

[jjzepplin]

I wired my truck with two batteries and two solenoids and an isolater. When I turn the key it gets starting power from both batteries. When its running it is only running off one battery but charging both. I run my trailer brakes and other accessories off the second battery. Camper etc. A tough concept to wrap your head around but I had hard starting problems even with a new switch. Now if I want to bump the engine I just put my starter switch on the solenoid right there by the battery. Much easier than fighting my way through the header with a small alligator clamp and hoping I find the right lead when I cannot see a thing. OH yeah and that mutha will start a tractor and my truck at the same time now! (stock starter too) around 9.5-10.0 compression I guess.
It isn't "pretty" but my wife is!

[no1udknow]

I'm gonna say +1 on the heat soak. My old man had a 72 and everytime it got hot, started cranked slow like it had a dead battery. Let it cool down for about 20 minutes... fired up just fine. If your running headers its even more likely. The other thing is to make sure you don't have a leaking valve cover on that side (everyone swears their sh!# don't leak when I say that) but oil will soak into the starter and dirty up the carbon brushes. If it becomes an ongoing problem, I suggest the remote firewall mounted solenoid route... pretty simple to set up.

[RichardJ]

MarkDTN you must be referring to this setup.




All switch's and relays have resistance. The ford relay adds resistance to the battery cable. The two extra cable ends and the nuts holding them to the ford relay can add extra resistance as well as two new points for possible corrosion.
The relay itself adds an extra drain on the battery at the S terminal.

You said "it just doesn't have to rely on the long length of purple wire to get power".

The purple wire is still just as long and instead of going to the S on the chevy solenoid, it goes to the S terminal on the ford relay.
The ford solenoid is actually just a relay, because it doesn't move the starter gear like the Chevy solenoid does. Now you have both.

The first drawing below, shows the basic chevy wiring. The Purple wire from the ignition switch goes to the S terminal and activates the solenoid when the key is turned. The battery is connected directly to the Chevy solenoid.

The second drawing shows the small Bosch type relay connected to the Purple wire. Current flows from the Purple wire, through the relay to ground. Less than 50 milliamps has to flow through the ignition switch and relay.

When the relay is energized, current flows from the 12 V source through relay terminals 30 to 87 and back to the S terminal on the chevy solenoid.

This relay wiring has far less drain on the battery and is much, much easier to install.

[MARKDTN]

Originally Posted by RichardJ

MarkDTN you must be referring to this setup.




All switch's and relays have resistance. The ford relay adds resistance to the battery cable. The two extra cable ends and the nuts holding them to the ford relay can add extra resistance as well as two new points for possible corrosion.
The relay itself adds an extra drain on the battery at the S terminal.

You said "it just doesn't have to rely on the long length of purple wire to get power".

The purple wire is still just as long and instead of going to the S on the chevy solenoid, it goes to the S terminal on the ford relay.
The ford solenoid is actually just a relay, because it doesn't move the starter gear like the Chevy solenoid does. Now you have both.

The first drawing below, shows the basic chevy wiring. The Purple wire from the ignition switch goes to the S terminal and activates the solenoid when the key is turned. The battery is connected directly to the Chevy solenoid.

The second drawing shows the small Bosch type relay connected to the Purple wire. Current flows from the Purple wire, through the relay to ground. Less than 50 milliamps has to flow through the ignition switch and relay.

When the relay is energized, current flows from the 12 V source through relay terminals 30 to 87 and back to the S terminal on the chevy solenoid.

This relay wiring has far less drain on the battery and is much, much easier to install.

I understand all of what you said, but that is not how people fix a hot start problem on a Chevy with headers. That is not how Ford got their Delco starters to work with 429/460 power. The Delco starter solenoid uses much more amperage to pull in than the Ford solenoid. That is because the Ford solenoid only moves a contactor while the Delco one moves the starter drive in as well-which you said. That is why people hook up the Ford solenoid. The small Bosch relay alone may help, but you still have to overcome the starter drive pull in.

"This relay wiring has far less drain on the battery..." You should not have any drain on the battery with any of these so not sure why you say this?

"...and is much, much easier to install." Not really. You still have to tap into the purple wire, and battery power and ground. All of these options are ugly underhood and take away from the simplicity of the truck wiring.

I meant to add to my post that I would not do any of these. I would swap to a gear reduction style starter. Heat issues are greatly reduced.

[67ChevyRedneck]

Remote solenoids, etc. are unnecessary as long as you don't have headers right on top of the starter. GM makes a simple solenoid heat shield. I had the same heat soak problem with my ram horns. Solenoid got hot, wouldn't start. I added this little booger with some of the heat tape stuff added for extra measure (never replaced the solenoid) and it hasn't had a starting problem since I added it in 2006.

http://shop.advanceautoparts.com/p/d...ontent=5706971

There are a couple versions, just make sure the screw pattern matches the screw pattern on your solenoid. I think this one should work for most of us.