The starter drive isn't engaging the flywheel teeth properly. Personally I would have stayed with the 6v starter. I had a similar issue with my 53 when I converted it to 12v. My issue was the solenoid. The 6v solenoid, on 12v, would start the starter motor before the teeth were completely engaged. I put a 12v solenoid on the starter (the starter itself is still 6v) and no issue since. Your truck should have the mechanical, foot operated, solenoid though (AKA stomp starter) so that should not be an issue.

The first thing I would check is the placement of the starter switch on top of the starter. If it's too close to the device that pushes on it, it would do the same thing (start the starter spinning before it's engaged with the flywheel). If the rebuilder put the wrong switch on the starter, and the shape of the switch makes the switch contact button too close to the foot device, the result would be the same. To me it almost has to be that dynamic relationship between the foot device and the starter switch on the starter housing (assuming you still have the foot starter). If you've converted to electric starting, try putting a 12v solenoid on it.

Thanks for the advice tiny.. i still do have the foot starter mechanism. I took a look at where its at on top of the starter and its the same one i was using before the rebuilder repaired it . Well at least it seems like it is . It sits on top mounting with two screws and when i replaced it in the past all it looks like its doing is transfering the 12 volts to the inside of the starter correct ? So just wondering should i even start messing with that what i mean,  is there a right or wrong one ? Its not like yours where its a 12 or 6 volt selenoid right? 

If it was me I'd have someone operate the starter pedal while I watched the mechanism to see why/if the button is being pressed before the starter drive is fully engaged. If it's fully engaged when the button is pressed and still making the noise it may be a bad starter drive although a bad drive doesn't usually make a grinding/gnashing noise. At any rate, getting a good look while it's being operated may give you your answer.

  Tiny i need to circle back on this topic. So the starter has burned out already. I was reading all the advice you were giving me again and i dont quite understand when you say the starting button that sits on top of the starter might be to close to the starting mechanism that pushes the button  to kick out the teeth of starter to flywheel . Heres what i dont understand . I asume the teeth of starter dont kick out to starter untill the button gets pushed but u seem to be saying the teeth should get kicked out and then start spinning once there synced with flywheel how would that be if its a push start and it gets power at once . I believe a electric start would probaly kick out teeth and then spin teeth almost like a two part start ( maybe thats what a selenoid does ) .. i plan to take starter to get rebuilt again and posibly tell them to make it 6v again but i would like to correct issue this time please maybe shine some light on this for me thanks for all ur help 

I think we need to see pictures of your starter as it sits in the truck, showing the foot start mechanism. The lever that pushes against the starter button on top of the starter extends past the pivot point, into the starter case and pushes the starter gear rearward to mesh with the flywheel. It should have the gears engaged before it makes contact with the starter button on top of the starter. The video in the link below shows that action. Your starter set-up should be very similar to the one shown. If it's contacting the starter button prior to the gears being engaged, it will grind. The video is not mine. I found it on the internet.

<CLICK ON ME>

@facundo As a test, you could loosen the starter mounting bolts and place a washer or shim of some kind, in a place that would tilt the starter to aim the engaging drive away from the flywheel. (I hope this makes sense) Retighten the bolts just snug so you do not break an ear off your starter. Give it a try. and serif the drive engages and starts your truck. You might be able to accomplish this test by just loosening the bolts until the starter will wiggle and pushing the forward end of the starter toward the engine while attempting to start.

The starter drive fits from 1938 to at least 1949 (that's the newest catalog I have handy) so it is unlikely the rebuilder replaced it with one that is incorrect. I was not able to look at the video. The correct linkage setup for your truck would be one where the pushing of your foot starter pedal first engages the drive mechanically and the lever that accomplishes this, pushes the switch to energize the starter. It is hard to imagine what might have changed, during the rebuild, that would change the geometry enough to cause your problem. Your starter does not need another rebuild but if one of my tests results in a successful start, that information would be useful to your rebuilder in helping you to solve the problem.

Mike

Thank you tiny i was able to see the video and that is exactly how my setup operates and looks like . As soo has i get starter back in i will send some pics . Mike thanks for the tip i will give this a try aswell .. 

This thread has been helpful to me, as my starter is still sitting on the bench awaiting installation. I looked at the lever on it and saw that someone had added material to it so that the electrical contact would be made earlier. Perhaps that was needed in an earlier life, but now it seemed to be a bad idea as the starter has been changed and a new switch is in place. I ground off some of the added metal and will see how it performs.

Something I have found before on this site...information that I didn't know I needed!

Thanks!

Thank u all for the support. I have an update .. i took the starter to a well known old school repair shop here in balwin park ca .. i told him all that  was going on and what had been done to starter . Once he opened it up he said it looked like a good repair job from the last repair where they converted to 12v .. what was wrong this time was the two fields that are stuck on the shell i belive theire called fields they were shorted .. so he repaced the shell and i reinstalled it and inhave no more hitting on flywheel .. no sure if maybe the fields were bad and causing it to pop out defectivly .. idk but its sounding good on start up now 

Excellent! Glad you got it figured out.