8111 DT&I motor binds up

I'm not an expert in Pullmor motors, but I had a very similar issue with one of mine. There's a little set screw (like 0.050" hex or so) in the brushplate on the end of the armature that you can use to tune the distance that the armature can "climb" when it changes direction. I would suggest turning that set screw down a little bit so that the armature doesn't climb out of position. I also replaced the motor brushes in my Pullmor and lubricated thoroughly (including a drop of oil on the backside of that set screw) which greatly improved performance.

Looks like your missing the "thrust bearing screw #8030-118" that goes on top end of armature in brush plate. Then you can adjust armature play. Screw may be there but its screwed in to far and can't see it. Also check lower armature bearing hole for debris and relube.

^^Ken and ^^Frank nailed it.  The only thing I would add, is to make sure all old hardened grease is removed from the "sump."  Then relubricate with a fresh teflon grease.  As long as the worm wheel in the truck isn't chewed up you should be able to restore smooth operation in both directions.

Your brushplate is black so it's difficult to see in your photos.  The "bump" that sticks up exactly halfway between the brush wells is meant to hold a tiny, fine-threaded Allen screw (part number referenced above.)  And the purpose of that screw is to limit vertical thrust play of the armature.

Your armature does seem to have some extra movement.  I had a MPC 8361 Alco with the same drivetrain as your DT&I that I got when I was 6 years old.  It had a million miles on it and the spur gears in the truck were worn to the point of almost falling off their studs.  It still ran smoothly in both directions, so I don't think that's the problem.  Could you swap in another armature and brushplate to test?  Worst case, you should be able to find another MPC power truck with AAR type A side frames for small money on eBay.

I am so sorry! I posted a different brushplate! Mine is a closed cap. Here’s the correct picture snd I’ll delete the incorrect post. I don’t see where a screw would go.

Hm.  I'm sure you could get the later brushplate from any major Lionel parts vendor.  The ones I've seen are usually white nylon.  You could also remove the one you have and drill it out from the inside to take the screw.  Others on here could probably tell you what size the body drill would have to be, to achieve a snug "factory" fit.

Before doing any of that, I would temporarily swap in another armature and brushplate to rule out any issues with the gears in the truck.  My $.02.

Some used a tiny ball bearing in the plate. I've used a ball from one of those ball key chains.

Try running it with this screw removed.