'84 300TD Solenoid sticking...ring gear?
 

My car has developed an intermittent problem. About one start out of 30 it fails to crank. I've traced the solenoid wire up to a terminal block on the passenger side to crank the engine independently from the starter key. When the car fails to crank, jumpering here to +12 causes sparking, but the solenoid does not engage. I took the starter out and had it rebuilt by the local shop. They replaced the solenoid and brushes...but the problem persists. When this happens, when I whack the starter, it will crank again. My guess at this point is the ring gear has a few bad teeth that sometimes coincide with the starter drive
(like a roullette wheel)....

any suggestions are appreciated!!

What are you using to jump the terminals? I suggest a fairly heavy guage wire.
When you club the starter to make it start usually what is happening is the brushes are seating on the armature and making better contact. If this is the only thing that helps I would be inclined to try another starter. I understand they are a ***** to replace so you might want to talk to the rebuilder first.

dsmess,

Ring gear wil not effect the solonoid working because ring gear is not connected to the pinion gear until after the solonoid actuates (pushes the pinion gear into mesh with the ring gear?

A bad ring gear may cause grinding when the ring pinion gear try to mesh but that means the solonoid has worked.

The current that goes thru the pick coil in the solonoid goes thru the starter so the started has to conduct current for the solonoid to work. So an intermittent starter can cause the solonoid not to work.

P E H

maybe totally off here,
 

but did you eliminate the nuetral safety switch as the culprit? sounds like a starter issue, but maybe next time it happens, try shifting to n and starting.

Thanks for the reply.
I was jumpering with a heavy wire...saw sparking but heard no solenoid engagement. When the starter was not 'locked' this would spin the starter fine.
The shop (I've been going to them for 20 years) said they replaced the brushes.
I figure the solenoid is stuck because I hear no sound when jumpering the solenoid terminal to +12. I picture the ring gear teeth not meshing with the starter drive.....but may be wrong!

Note, the symptoms are the same before and after the starter work.

Are you saying poor brush contact can prevent the solenoid from actuating?
This could explain things....but the solenoid is drawing current (sparking) when it is jumpered to +12V.

It's possible the job bungled things

Interestingly...I had problems with the neutral switch at the same time.
I replaced it...still have symptoms as described.

dsmess,

Yes, bad brushes or a dead spot on the starter commutater can cause the solonoid not to work.

There are two coils in the solonoid: pick coil and hold coil. Current energizing the pick coil goes thru the starter and then to ground. Once the contacts in the solonoid close, the pick coil is not energized because it is shunted by the solonoid contacts. The hold coil current goes directly to ground so it is energized as long as the key it turned to start position. But the hold coli does not have enough magnetic flux to make the solonoid actuate. So U will see some spark when U jump 12 volts to the solonoid start terminal even if the solonoid doesn't actuate.

P E H

PE...I'm impressed and humbled by your knowledge. I thought the solenoid had just a single coil. I've been dealing with this on a 2000 mile road trip..and the solenoid issue along with the bad neutral switch has driven me nuts. I'll be pulling the starter and raising hell at the shop.

Thanks a lot

dsmess,

The shop should have machined the commutator or at least sanded it and then checked the armature with a growler. That's a magnetic device that tests for an open or short in the armature.

If one of the segments of the armature is open and that section stops directly under the brush, the solonoid won't work because no current will go thru the pick coil. That's one way the problem can be intermittent.

I had an old Ford many years ago that had an open segment in the armature. Every once in a while, the starter wouldn't work and I had to move the armature with a screwdriver to get the car started. I was a teenager then and didn't have enough money to replace the starter, so had to put up with it.

The pick coil pulls a lot of current but only for an instant until the solonoid moves and closes the contacts that energize the starter. The lower current hold coil keeps the pinion gear engaged in the ring gear and the starter cranks the engine until the key is released. And that's the way it works.

P E H

I second P E H
My wifes '84 wagon did the same thing and the commutator on the armature had a dead segment. I replaced the armature and it worked fine