Starter disengages during cranking

[Infinite Monkeys]

The engine is a 390 with a COM with vacuum modulator in a '60 T-Bird.

The starter disengaging during cranking is an intermittent issue, but I'd hate to be stranded somewhere because of it.
I've never had to deal with this issue, so I'm at a loss for ideas.
So basically what happens is that sometimes while cranking the bendix will disengage and spin free, at that point I stop cranking with the key, wait for the bendix to stop spinning and it will then re-crank and start the car without a problem.
Any thoughts are appreciated.
Thanks.

[simplyconnected]

Put your starter motor on your work bench, and take the inspection plate off. Look at the commutator segments and brushes. If the segments look good (no black burn marks, taper or egg-shape, go on to the brushes. If the brushes look bad, replace them.

Your Bendix gear is supposed to disengage anytime power is interrupted or when the flex plate rotates faster than the starter motor.

If all looks good, your Bendix gear is probably going south. Buy and install a new one or trade-in your starter motor for a remanufactured one. - Dave

[Infinite Monkeys]

Put your starter motor on your work bench, and take the inspection plate off. Look at the commutator segments and brushes. If the segments look good (no black burn marks, taper or egg-shape, go on to the brushes. If the brushes look bad, replace them.

Your Bendix gear is supposed to disengage anytime power is interrupted or when the flex plate rotates faster than the starter motor.

If all looks good, your Bendix gear is probably going south. Buy and install a new one or trade-in your starter motor for a remanufactured one. - Dave

Couple of things I'm curious about:
One is..... does it mean anything if the bendix continues to spin after it disengages.
And second, I sometimes hear the bendix continue to spin for a second or so after the engine has started.
Do either of the two conditions mean it's probably the bendix? I'm planing on changing the brushes anyway, I'm just wondering.

Thanks again.

[simplyconnected]

The Bendix gear is driven on the shaft of an electric motor. When working properly, the gear locks on the shaft in one direction as long as it is rotating in that direction almost like a socket wrench ratchet. And like a broken ratchet handle, when a Bendix gear starts going bad it will simply 'let go' when it's supposed to be locked.

The motor armature is hefty and spinning fast. Of course, the motor will keep rotating even after power is removed, simply from kinetic energy.

When the engine starts, the Bendix is still engaged but the flex plate starts going faster than the starter motor, still rotating in the same direction so the ratchet direction is still satisfied. Since the flex plate is going faster than the Bendix gear, the gear stays engaged but it free-wheels until starter motor power is removed.

When you let go of the key, power is removed from the starter motor. Rotation slows, the Bendix gear disengages and returns to the 'home' position, ready for the next cycle. If your starter motor doesn't perform as described, it needs maintenance.

Your starter motor brushes come in two sets of two (four all together). Two brush pigtails simply bolt onto the case which is grounded to 'chassis'. The other two are soldered under a folded piece of metal. You will need a large soldering iron to remove the old and replace with the new. Original soldering irons were simply held in a fire until hot. They were made of iron to hold heat. You can heat a hunk of steel with a propane torch to accomplish the same thing. The iron should melt lead but red hot is too hot. Touch the connection with your home made iron and pull the old pigtails out with a pair of pliers because the connection is crimped. Reverse the procedure for the new brushes but add a little more solder after you crimp it.

Make sure your new brushes slide easily in their brass holders. They need to be smooth with no obstruction. I simply bend a short length of coat hanger on the end and pull the pigtail up and down as I watch the spring tension pull the brush back down.

When done, this job is very rewarding and you will save a bunch of money. Take lots of pictures as you go. - Dave

[Infinite Monkeys]

The Bendix gear is driven on the shaft of an electric motor. When working properly, the gear locks on the shaft in one direction as long as it is rotating in that direction almost like a socket wrench ratchet. And like a broken ratchet handle, when a Bendix gear starts going bad it will simply 'let go' when it's supposed to be locked.

The motor armature is hefty and spinning fast. Of course, the motor will keep rotating even after power is removed, simply from kinetic energy.

When the engine starts, the Bendix is still engaged but the flex plate starts going faster than the starter motor, still rotating in the same direction so the ratchet direction is still satisfied. Since the flex plate is going faster than the Bendix gear, the gear stays engaged but it free-wheels until starter motor power is removed.

When you let go of the key, power is removed from the starter motor. Rotation slows, the Bendix gear disengages and returns to the 'home' position, ready for the next cycle. If your starter motor doesn't perform as described, it needs maintenance.

Your starter motor brushes come in two sets of two (four all together). Two brush pigtails simply bolt onto the case which is grounded to 'chassis'. The other two are soldered under a folded piece of metal. You will need a large soldering iron to remove the old and replace with the new. Original soldering irons were simply held in a fire until hot. They were made of iron to hold heat. You can heat a hunk of steel with a propane torch to accomplish the same thing. The iron should melt lead but red hot is too hot. Touch the connection with your home made iron and pull the old pigtails out with a pair of pliers because the connection is crimped. Reverse the procedure for the new brushes but add a little more solder after you crimp it.

Make sure your new brushes slide easily in their brass holders. They need to be smooth with no obstruction. I simply bend a short length of coat hanger on the end and pull the pigtail up and down as I watch the spring tension pull the brush back down.

When done, this job is very rewarding and you will save a bunch of money. Take lots of pictures as you go. - Dave

Dave,

I am truly impressed with your ability to explain how to do things in writing. This is not an easy thing to do. I mean this sincerely!!
As always, I appreciate the help.
Thank you.

[simplyconnected]

FINALLY, someone who actually reads my long-winded essays!

Kinda joking but Robin (my wife) claims that most folks only read the first and last part. They don't have time for the whole thing. I listen to her because she's a teacher and I'm her biggest student.

Thanks for the kudos, iftikhar. - Dave