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1966 Riviera starting issues


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The fact that the battery has 12.6V doesn't mean that the starter does. The GM starting circuit runs through a number of connections and switches, each of which degrade over time and introduce voltage drops. Check the voltage at the solenoid itself while cranking.

 

start-ppt-download.jpg

 

Also, when was the last time the starter was rebuilt? The disk and contacts in the GM solenoid get pitted from use. Eventually they won't make sufficient contact to turn the starter motor, despite the fact that the solenoid clicks.

 

diy-auto-service-starters-diagnosis-and-

Edited by joe_padavano (see edit history)
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I agree with Joe start by making sure you have 12.6v at the main battery connection at the starter. If not go to your horn relay. GM used the horn relay as battery distribution junction point. What happens to your voltage when you try to crank the engine? Does it crash or does it maintain? Crashing generally indicates at battery issue. Maintaining indicates a cable issue.

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9 minutes ago, certjeff1 said:

I agree with Joe start by making sure you have 12.6v at the main battery connection at the starter. If not go to your horn relay. GM used the horn relay as battery distribution junction point. What happens to your voltage when you try to crank the engine? Does it crash or does it maintain? Crashing generally indicates at battery issue. Maintaining indicates a cable issue.

 

Actually, the problem isn't the main battery connection, it's the small "S" terminal on the starter solenoid. That's where the voltage drop occurs, due to the lengthy run of the purple wire from the junction box through the firewall to the ignition switch to the neutral safety switch through the firewall again and ultimately to the starter. Coupled with resistance in the solenoid contacts due to pitting, this is the most frequent cause of start problems on GM starters. Of course, also ensure the starter brushes aren't excessively worn, either.

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I would do a quick check of the battery by putting a volt meter on the battery terminals and try to crank the car.  If the battery still reads 12.6, then the above diagnostics are good.  If the battery voltage drops to something less than 11 or 12Volts, then I would guess bad battery.

 

Just curious, how old is the battery?  If it is over 4 or 5 years old, I would suspect possible battery.

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On 2/22/2021 at 8:28 AM, joe_padavano said:

That's where the voltage drop occurs, due to the lengthy run of the purple wire from the junction box through the firewall to the ignition switch to the neutral safety switch through the firewall again and ultimately to the starter.

 

Not in the OP's case, but Corvairs and Corvair FCs have this problem because the run is even longer than front engine vehicles. Lucky usually cleaning the connectors solves the issue. If not, new harnesses are available. 

 

Then there is the Ford solenoid trick. Not a proper repair/modification at all, but works! A common 6 volt VW fix. 😉  Why does it work? Because the Ford solenoid pull in current draw is less than the GM, as the GM is also developing the force to pull in the starter drive system.

 

Bryan, just do as Larry and Joe say, measure the voltage at the S and big terminal where the battery cable attaches while someone turns the key.

 

Breaking news, put brushes and bushings in the starter and you will be OK. The mallet usually seats the brushes to get a few starts, but it will fail again.

Edited by Frank DuVal (see edit history)
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12 hours ago, Frank DuVal said:

 

Then there is the Ford solenoid trick. Not a proper repair/modification at all, but works! A common 6 volt VW fix. 😉  Why does it work? Because the Ford solenoid pull in current draw is less than the GM, as the GM is also developing the force to pull in the starter drive system.

 

The Ford solenoid is a band-aid. It works because the solenoid bypasses the voltage drop in the GM wiring and applies battery voltage directly to the S terminal on the GM starter. An relay controlled by the purple START wire and with the switched terminals between the battery cable and the S terminal on the GM starter would do the same (and avoids the stigma of using Ford parts in your GM). That's also a band-aid.

 

To the OP: if your "one year old" starter is a rebuilt or imported new build, it likely has sub-standard brushes and solenoid contacts. Many of these new starter solenoids use internal contacts that are thinner and of a less robust material than OEM. This is why I rebuild my own, using GM parts.

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On 2/23/2021 at 10:46 PM, Bryan C. Robertson said:

Gentlemen, thank you for that detailed input.  All connections were cleaned, inspected, and tested for voltage.  Thereafter I took a rubber mallet and banged the starter 5 times and she started right up!  Battery is only 1 year old as is the starter.

You're starter likely needs brushes. The circuit for the solenoid goes through the starter on Delco. The brushes getting iffy, nothing happens when you try to start. Bumping the starter jars the brushes a bit and they will connect. Forget the band aids. Pull the starter and fix it. 

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