How can I start the reclass process? Do I have a good chance to switch to 19K?

With that degree of familiarity with armor, you should have a lot going for you. Check with your unit's equivalent of an advisor or take it up the chain. Somebody should be able to assist you.

Go see your Career Counselor

Check with S1 and pick up 19K as a secondary MOS.

I was giving this some thought in hindsight. I was thinking it might be good if 19K and 91A could cross train. Just for those SHTF scenarios.

Reclass when you re-enlist. Only way I know of. Your maintenance skills will be welcomed by whatever crew you serve with. Good luck to you and thank you for your service.

You need to talk with the Personnel Support for your unit. Reclassification is usually based upon the he ‘needs’ of the Army. Think you would be as asset as a crewman since you know the technical aspects of the M1! Good luck!

Talk to your unit retention.

I was told I needed to reclass when my 42A S-1 spot was leaving with the unit and I couldn't go with, so I became a 21E which is now the 12N (Human Resources to Horizontal Construction....what a jump). I'd also love to know what the proper process would have been instead of "hey you can't leave so you have to reclass."

having 10 shop and 20 shop skills certainly helps matters.
and the familiarity with deadline reports mechanic side is a bonus as well.