Weird Electrical Question-Help Needed

[Dirty Marty]

Fellow Pelicans,

My 70 911T is having a weird come and go electrical issue. The car sits in the garage most of the week and I drive it on weekends. Lately, when I fire it up for a drive it starts up and I head into our small town on an errand about 5 miles. When I get back in to start it to go home- I get the infamous solenoid click but no start, unless I push start it. Then when I get home I let it sit for a while and it starts like nothing was wrong. It's done it a few times now even after I've let it have a trickle charger on it over night.

What gives?

Dirty Marty
Fallbrook, CA

[911pcars]

Common issues for this symptom:
- loose and/or corroded battery connection (either cable)
- malfunctioning starter
- borderline battery
- combination of any of the above

Sherwood

[Targa Me]

^^^
Can we add starter solenoid to that list?

[964TargaC2]

sounds like dirty marty has dirty connections, start with cleaning battery terminals and connectors paying attention to where ground attached to frame , then clean connections at starter

[911pcars]

Originally Posted by Targa Me

^^^
Can we add starter solenoid to that list?

Of course. I used the generic term, "starter" to CMA (includes motor, solenoid, over-running clutch, brushes, field windings, etc.).

Sherwood

[silverc4s]

try to get someone to do a dynamic test of your battery and charging circuit. Snap-on and others make a tester for this purpose.
My 1970 with an external regulator had symptoms like this, and it turned out to be bad radio supression capacitors attached to the regulators terminals. They can be completely removed and the charging circuit will work just fine.
This tip courtesy of Ed Mayo, one of our national gurus..

[blucille]

Also, the start circuit of the ignition switch can go bad and wouldn't you guess it often works a couple of times but after a couple of starts won't give you another for a while.

Still, I'd say most likely is the starter motor itself/solenoid, etc. you can whack the starter with a hammer when it's misbehavibg. That's as close to a 100% confirmation as you will get.

[wwest]

The solenoid/bendix must "full travel" in order to supply full 12V power to the starter commutator.

Apparently it isn't when hot.

[sugarwood]

Should he measure 12V at the battery to rule out the battery?
Or is this already accepted since it starts the next day.

[T77911S]

all VERY good advise. start with the simple stuff first.

you can have 12v at the battery/starter but not enough current to pull in the solenoid.
it takes a lot of curent to pull in the solenoid.
what happens with the solenoid is the contacts inside get burned/corroded and it does not provide the current to the starter motor to turn over. the solenoid can be removed and the contacts cleaned and rotated. only about half of the contact is used so the other half looks like new.

the yellow start wire is very long and goes thru several connectors. corrsion at these connections can reduce the current.
also, if you have a car alarm they can also cause the same problem

[Dirty Marty]

Thanks to all of you for your advise.......I will start with the simple stuff and go from there.

Dirty Marty
Fallbrook,CA

[wwest]

Originally Posted by T77911S

all VERY good advise. start with the simple stuff first.

you can have 12v at the battery/starter but not enough current to pull in the solenoid.
it takes a lot of current to pull in the solenoid.

No, trivial level of current flow compared to once the solenoid full travels enough to push the starting gear into contact with the flywheel ring gear and then closes the contacts to the starter motor.

what happens with the solenoid is the contacts inside get burned/corroded and it does not provide the current to the starter motor to turn over. the solenoid can be removed and the contacts cleaned and rotated. only about half of the contact is used so the other half looks like new.

the yellow start wire is very long and goes thru several connectors. corrsion at these connections can reduce the current.
also, if you have a car alarm they can also cause the same problem

The "CLICK" you hear is the solenoid being positively engaged, and more likely than otherwise moving the starter gear into engagement but the electrical contact to the starter not closing due to wear.

You can disassemble the starter solenoid and rebuild the electrical contacts with high temperature (high silver content) solder.

See:

https://www.youtube.com/watch?v=ITFW2PkqXWw

[T77911S]

i usually just clean them and rotate the contacts.

SOLENOID and STARTER rebuild......finally