Jump to content

Delco motor-generator 1916-1925 question / problem


Recommended Posts

These units contain generator and starter motor in one. They were supplied in my 1924 Cadillac, but I suspect they were all the same from some time in the teens till the end of the 1925 model, and possibly in other makes and models also. Mine is "shorting" somehow. The generator circuit is supposed to receive electricity when the ignition switch is turned on. This starts the motor turning slowly (while the gears engage), and a subsequent operation (depressing the pedal) stops this action and replaces it with the stronger, faster motor circuit turning instead. Problem I am having: the generator circuit won't disconnect when the car is turned off, so the only way to stop it turning is by disconnecting the battery. Problem began intermittently, now is persistent. I have checked the ignition switch to confirm it is not the problem. Somewhere I suspect in the motor generator a wire is getting fed electricity that it should not. I intend to remove the whole unit and start carefully checking it over, but am writing in the hope someone will have useful experience they can share with me on these motor generators. Thanks, Mike Barnes, Canada

Link to comment
Share on other sites

Mike Barnes,

When the ignition is turned on, a small amount of current is supplied to the armature circuit which makes the armature spin slowly so that the gears engage when the starter pedal is depressed. The first part of depressing the starter pedal disengages a small brass finger switch just above the starter brushes which interupts the current going to the armature (generator) circuit. Further depressing the pedal engages a differant set of brushes for the starter. After the engine starts and the starter pedal is raised, the finger switch reengages the generator circuit. If the generator is spinning after the ignition is off, one possible reason is the armature wire that is routed in between the heavy gauge starter field coils and the case is getting shorted against those coil wires. Those heavy gauge starter coils are always connected to the battery. The armature wire cloth insulation likely deteriated causing the short. Disconnect the armature brush wire from the brush and use continuity meter to verify the short. Remedy is to route a new wire through the coils from finger switch to the armature brush. Tricky to do if the DELCO unit is in the car, better if the unit is out of the car.

An article on the DELCO unit for Lincoln is at:

Lincoln Model L Engine Compartment Detail Information

Link to comment
Share on other sites

  • 9 years later...
On 9/10/2012 at 11:00 PM, startergenrebuilder said:


Hopefully I can help you. I work on these units fairly often. Feel free to contact me with details, either directly by email or by phone. Theres a number of things to check, I'll wait to hear from you and hopefully I can shed some light on your problem.

Hi Jason, 
I have a 1925 Lincoln Model L with the Delco Starter/Generator. This was working and then yesterday we tried to start the car and when you engage the starter the generator just shuts down. Any ideas on what the issue might be? Thanks.

Brandon Hilton

Edited by Brandon Hilton (see edit history)
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...