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1956 Buick 4 Jet....intermittent petal crank... neutral safety switch or accelerator vacuum switch? Help!


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I'm trying to troubleshoot my issue getting car to crank.  Turn ignition on and press petal and nothing happens...sometimes.    Turn key on and off several (or a LOT of) times then suddenly I get crank.  Shut right down and it may or may not crank again?   At first I though the neutral safety switch being wonky as my first experience seem to be shift to N and back to Park got it to work but now not so sure.  Why would it intermittently work?  Anyone with any experience on this?   I'm looking at the diagram of the switch, maybe contact spring needs replaced or switch dirty?  I'm afraid to pull it apart are there any available?

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No direct experience but it could be a myriad of possible things. Start with the simple things and go from there. I assume you have the shop manual? If it is intermittent then it will be more difficult to find the fault but I would start with a test light or similar and start confirming where live power is getting to.  The shop manual will show you how the power travels.  Follow the path and check firmness of connections as you go. This could be something as simple as a connection issue with the ignition key to an issue with the starter solenoid and anything in between.  I know the nuetral switch can require adjustment and if that was out then that could be affecting the ability to start but a simple test would be to bypass that switch and see what happens. I have tackled similar electrical issues so I certainly don't envy you but you will find it eventually. Someone else will chime in with some more ideas but let us know how you go.

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I tapped on the vacuum switch lightly with a wrench and just did 5 start cycles with no issue. I drove it around the neighborhood, shut it down  and then started it again with no issue.  That surpasses the record of 2 starts in a row with no problem.   I do have the manual and I'm leaning toward the check ball may be getting gummed up and not falling back into the non-running position after shutdown.  I'll see what happens in the morning.  I may not need to break out the multimeter. 

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If it doesn't engage the starter in the am then jump the two wires at the switch momentarily to see if the starter engages.  Is so, likely the accelerator starter switch.  If not, then maybe the starter relay. 

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Cars will try to mislead you. Thoroughly clean your battery ground cable at both ends. If the clamps on your battery terminals are clamped down all the way take the bolt out, spread them, and fine away some of the old squished lead so they fit right.

 

Don't assume anything is right. On the times it doesn't start, have you turned on the headlights to see if they stay bright or dim?

 

It could also be just a loose wire on the pedal switch.

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1 hour ago, 60FlatTop said:

 

Don't assume anything is right.

I hear you! Had no issue this morning.  Drove it to the tire place to get some whitewalls put on and once again no crank.  I jumped the vacuum switch leads with a screw driver and crank!   So if the switch leads had power...not neutral safety switch.  I got back in car and it immediately cranked and started from the petal.

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3 hours ago, avgwarhawk said:

Please disconnect the battery before you start working on this carb. 

Yep, those wires to the start switch are not fuse protected and if shorted to ground will instantly fry your complete harness.  Same for the horn relay.

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On 5/21/2021 at 9:27 PM, redapache59 said:

I tapped on the vacuum switch lightly with a wrench and just did 5 start cycles with no issue. I drove it around the neighborhood, shut it down  and then started it again with no issue.  That surpasses the record of 2 starts in a row with no problem.   I do have the manual and I'm leaning toward the check ball may be getting gummed up and not falling back into the non-running position after shutdown.  I'll see what happens in the morning.  I may not need to break out the multimeter. 

My money would be on the starter switch and the wires going to it.  Have had that exact problem with the passage that the check ball rides in getting gummed up, as well as the contacts inside getting dulled.  With the power off or battery disconnected you can also push the pedal down and measure the resistance across the carb switch.  It’s easiest to pull the carb off, disassemble the switch clean the contacts and the passages, don’t loose the shims and put it back on.

 

x2 on the power wire to the switch (yellow or pink) being unfused and burning the wiring harness - PITA to fix.  Also check the connector ends where they crimp onto the wire.  The wires on mine got brittle and started breaking off at the crimp points, had to replace them.

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Posted (edited)

Thanks for all the help.   I started the car at least a dozen times today with no issues (I also adjusted the choke).  The car wasn't being driven or started alot.   The check ball being gummed up seems to be the case.  

Edited by redapache59 (see edit history)
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