What causes a starter's pinion gear to engage/grind into the flexplate teeth while the vehicle is running in overdrive?

 

6MT or A4? Sounds like maybe a bad thrust bearing.

If its an M6

Get a mag base dial micrometer and figure out a position that it can read fore/aft crankshaft movement. Then have a buddy watch the needle and tell you the difference between the two while you push the clutch in and out. You might have to push the crank pulley back towards the motor while you have the pedal out to get an accurate reading.

I'm not real sure what the correct thrust bearing play is on LS1's but I'm sure that info is available somewhere. If I were to guess though its probably less than .003". Do this as soon as possible to prevent catastrophic failure if the bearing gets bad enough.

 

Ok, went and read your other post on this subject. Since your car is an A4 I seriously doubt its a thrust bearing issue, since I think I have yet to see any automatic motor with any noticeable amount of wear on the thrust surfaces.

Do you own a multimeter? It is IMO the first tool mechanics should be reaching for when weird problems arise. If not, get one then follow these steps.

1. Put multimeter in the 20VDC range
2. Use an aligator clip to put the positive terminal of the meter on your SWITCHED 12v + on the starter solenoid
3. Start the car and go through the whole P to N to D thing you were talking about in the other post
4. See if your multimeter shows ANY voltage to the solenoid's 12v switched wire, when the starter begins doing its weird stuff. If it does then you have some electrical issues you need to figure out


Also, I'm not too familiar with F Body starters but make sure the terminals on the starter are not cracked. I could see a short happening if the terminal block insulators (plastic **** under the connectors) are cracked. This would be even more so the case once you put the whole drivetrain under load (shifting into gear from park, being in overdrive on the highway)

 

Cracked flexplate, that's "getting crazy" ???

 

You guys cant be serious!!?!?? You know how far the flywheel would have to move to hit the starter gear?
Its a simple solution. One a tech that has taken apart a starter would know.
The bendix spring is broken. The bendix spring pulls the bendix back out when you let off the key, from the crank position. It also keeps the bendix pulled back as long as the keys not in the crank position.
Break that spring and the bendix is free to move back and forth.
Only other solution is theres a short to power in the crank circuit.

 

If the thrust bearing was completely missing, it wouldnt be able to move far enough for the flywheel to contact the starter gear.

 

...Thanks Drew04GTO...that's good stuff. I'll run through those steps tomorrow... I put a new ignition starter switch in the steering column and it's still doing it so I'm running out of possible causes (I know it's not the bendix spring).

The weird thing is that I can have the motor off, put the key in the forward position (but not cranking) and then just shift over to D and it starts by itself at that point...wierd....

Here are some of the knowns:
-installed a new PNBU safety switch/transmission range switch working
-Installed a new ignition starter switch,
-Installed a new Starter, Solenoid,
-Fuses are all good


So I start the motor and let it warm up to about 180degrees...then I pull the gear arm from P to R, and then From R to N......when I shift into D, the starter pinion engages the flexplate and grings like hell until I shift out of OD. So I've been driving around in 3rd most of the time. If the engine dies....all I have to do is move the shift back to OD (not Park of Neutral) and the starter automatically kicks in and starts the car by again..

It's defenitely an electrical issue somewhere......somethinig is tricking the PCM into thinking the starter needs power to start when it's in OD....

 

I thought you meant it was just running into the flywheel.
The PCM doesnt command cranking. The most likely cause is the P/N safety switch is shorted. Probably has the reverse light circuit (hot all the time) shorted over to the crank circuit, through the OD pin in the connector.

 

ed-cmat-lt,

Thank you, I think you are right...definitely a short....help me understand something, I put in a brand new P/N switch and new C1/C2 connector pigtails after this problem started...thinking that was where the short was...but that didn't fix the problem.... where else do you think the short could be?....

 

Maybe, next time, explain all the details??

 

Old Geezer...Where are you getting a "cracked flexplate" from?...

...maybe you aren't comprehending the "details"?....

 

what you first posted, then the next...
"What causes a starter's pinion gear to engage/grind into the flexplate teeth while the vehicle is running in overdrive?"

Then, after you get some responses, you come with:
"So I start the motor and let it warm up to about 180degrees...then I pull the gear arm from P to R, and then From R to N......when I shift into D, the starter pinion engages the flexplate and grings like hell until I shift out of OD. So I've been driving around in 3rd most of the time. If the engine dies....all I have to do is move the shift back to OD (not Park of Neutral) and the starter automatically kicks in and starts the car by again.. "
Your first post would lead many to conclude you were driving the car, and the trouble surfaced when it went to OD.
A cracked flexplate can make lots of noises. I posted that as a question.
I fully "comprehend" the details...... once you posted them.

 

The details are correct in both of my post...the issue is one in the same, again, the starter engages when the motor is already running (while driving in OD, when shifting into OD from P, N, etc)...Both Drewo4GTO and edcmat provided excellent analysis based on their individual experience(s)..(thanks guys). So, something is telling the starter to engage when it shouldn't...

btw- Old Geezer, I now understand your "cracked flexplate" comment...after reading your 2nd post (...which had more details....sound familiar?)...