I bought a used seatbelt assembly off of ebay and noticed that when i took it out of the box it was stuck. Otherwise, it looks like it's in decent condition. I feel like i'm missing something here though. Assuming it's not locked and/or broken from the airbag being deployed, is there a way/procedure to unlock and release some slack?

 

Sounds like the pre-tensioner has been fired, this happens if the vehicle was in an accident and an occupant was detected in the seat. The airbag and pre-tensioners fire simultaneously

 

If you plug it in to the car and turn the ignition switch on there will be an SRS code if the pre-tensioner has been fired I think.

 

Update: So i wasn't able to do an OBD scan, but i looked up how to test the seatbelt to see if the pre-tensioner was fired/deployed/locked with a multi-meter. I followed this youtube video.
here's a few pics of what i got after using a piece of sandpaper (whatever i had around) to block off the circuit. I was getting ready to send this to the seller to prove that dude must've sent me a bad seatbelt, but it looks like that's the reading that the guy in the youtube vid says i should see if it's still intact. I think i can see the physical piece that is meant to jam into the moving parts and lock it, but i'm not sure if trying to gently nudge that back will cause anything bad to happen.

(My car has always shown the airbag deployed light btw. I eventually learned that this car must've had some wicked impact on the passenger side and was repaired before it was sold to me. but outside of them apparently carelessly leaving sooo many traces of bondo everywhere, it wasn't a bad job at all. So this project though was to address the weak retraction in my seatbelt, which is when all the trouble started and i took apart the original one like a doofus instead of the shortening the belt a little)

 

Have you followed the checks in the FSM? There's an "Automatic Locking Retractors" mode for child seat usage, as well as off-vehicle checks where there can only be a certain degree of tilt or the retractor locks.

 

hmm, so i fussed with it again today and at some point it magically let go of some slack. and then i just fiddled with it until i was eventually able to get the whole belt out. I don't know if that means i'm out of the woods, but it was too late to fully install it. I'll report back how it acts when it's bolted up.

 

Ok if you're having problems with the seat belt retractors not being strong enough to pull the slack out of the belt when you unbuckle this is almost ALWAYS caused by decades of corrosion/buildup in the bearing (it's not actually a bearing) of the seatbelt. Take off that finisher panel over the retractor and spray the ever living bejesus out of the retractor with silicone spray. Every G35 coupe I've seen of this age has issues with the seat belts retracting weakly and I've fixed 5 of them with silicone spray and those belts retract better than new now.

 

I can't believe it. I bolted it on and it works! i guess i didn't understand how sensitive it was to orientation. So i have a working seatbelt again, but after buckling it and letting it go, i have the same issue i started with. I gave it a good cleaning and the contact points that the belt slides on, which helped a little, but now i'm considering a new theory. If i unraveled the belt carefully down to the base again, but this time just shortened the belt length by a couple inches, shouldn't that make it retract better?

 

ok i'm gonna try silicone lube first
and if that doesn't do it, i'll shorten the belt by like 4 inches and see if it matters