When the seat belt roller attempts to pull out, and then comes to a sudden stop, what needs to be addressed to fix it?

First, the reel has to be absolutely upright. There is an internal pendulum that will lock the belt if the reel is at an angle (or feels the effect of braking).

Second, there is a centrifugal lock (I think) that kicks in when the belt unspools too fast.

If any of the mechanism is gummed up, it will also tend to lock.

It worked before I removed it to unroll some to get clearance to get the bolt out.
Once off, and held upright, now it don't want to pull out.

So it can be cleaned?

See: https://914electric.wordpress.com/2011/09/2...elt-tightening/

I’ve used their cleaning routine several times. Easy and a lot less work that total disassembly.

My original seatbelts looked good, but didn't retract well. I removed them and put them in a box with all of the other original parts from the car that I've removed and installed new belts (Repa brand). The pair was under $250 shipped from Germany. Safety first and they look great. Simple, easy, direct fit (no mods needed):

https://www.ebay.com/itm/223236728044?fits=...9EAAOSwOVlb8YX1

If I'm reading correctly, he's having trouble with pulling the belts out rather than engaging. I have a freshly restored belt that is doing the same. Brand new webbing and they were supposed to clean the reel mechanism in the process, but don't have anyway to verify what was done without taking them apart. Regardless, new webbing so it should not be a dirt issue. It retracts just fine but I have to pull it out very SLOWLY to prevent the pawls from engaging and stopping the belt. I know that is common with belts of all makes to some degree, but this one is a bit extreme. The belt is installed properly in the correct orientation (pretty hard to install them wrong). I'm guessing a bit of teflon lubricant on the pawl mechanism might help but haven't ventured any further than guessing so far. Interested to see how this thread unfolds.

If memory serves, the pawls act on centrifugal force - the fast they spin, they more they engage outwardly. So...if you have to pull slowly, sounds like the part that keep the pawls retracted may be too weak?

I've been in a few of these reels but never disassembled that side completely.