Starter Spins, Will Not Engage Flexplate
 

Hey guys, finished up installing an AW4 transmission and NP242 transfer case into my 2WD Jeep (front axle coming soon! lol) but I can't test my work because the engine won't crank.

The starter spins and spins but it apparently is not engaging the flywheel.

Now, I disassembled the starter a few days ago when I took off the old transmission, cleaned and lubricated it. So, when it didn't work right I took it back off and made sure the bendix could move, and it can. I'm also pretty sure the wiring is correct cause apparently it will only go on one way.

Both my old 2WD transmission and my "new" 4WD transmission are from 1995 vehicles. Is there a part # difference for the starter here?

If anyone has the slightest idea or guess what my problem is let me know cause I sure don't.

Bench test the starter. If it doesn't engage it needs replaced.

Same starter as long as it's 4.0

x2

What exactly do you mean by bench test? Take it to the auto parts place to be put on the testing machine?

I did the at-home test w/ jumper cables with the starter outside the vehicle, the pinion spins and extends as you'd expect of a working starter.

well then your starter is engaging.. You have another issue. Have any more info you can give us?

Teeth missing out of flywheel?

Either what Toni said above me, or the bendix isn't fully engaging/extending.
Also check to make absolutely certain that the starter is fully seated in its mounting location.


Also, as stated by Cheddarnut, the starter is exactly the same as long as you took the 4x4 trans off of another 4.0 and not a 2.5.


Good luck, and let us know how it goes.

Just a thought,

Are you sure it's got enough power? Sometimes if the starter doesn't have enough voltage (battery problems, etc.) It will sound a lot like it's spinning but do nothing. Use whatever you're using to bench test directly on the starter in the jeep and see if it cranks then. Disconnect battery and ignition wires from the starter beforehand.

I was convinced my starter had busted it's teeth for a while last year and wound up just needing a new battery.

Edit: Even if you're jeep reads good voltage you might have a problem in your wiring.

RESOLVED
 

So, I figured it out. It wasn't the bendix, the flywheel, or the battery voltage. It was my fault. When I disassembled, cleaned and lubricated the starter, in my ignorance of the details of how an electric motor works, I put grease on the brushes and where they contact the magnets. Turns out that will allow the motor to spin but not enough voltage will get through (just like what Velcro said would happen if battery voltage was too low) in order to force the starter to engage.

I cleaned the grease off with a brake cleaner, and actually took a fine grit sandpaper to the electrical contacts that the brushes clamp down on, and afterwards everything fired up nicely.

New 4WD transmission works great too! :)