Hi. How do I lengthen a rear retractable seat belt

The likely cause is a broken spring/mechanism in the belt coil. I'm sure you can get a replacement for this belt.

all the jetta rear seats and seat belt parts
look the same sort of set up

fiddly job
back seat section or sections out
have to remove some plastics
to get to the retractable part of the belt ....looks like it is
under or mounted on the rear parcel shelf
undo the floor mount

then re thread and bolt the new seat belt in (pictured)

then replace the seats

didnt specify vehicle (generic answer) remove seats unbolt seat belts if attached to a seat -removable-just in bolt --before you do remove cover and check for debris or rust or if twisted

this is a ratchet seat belt, this is normal, it does this function for baby seats and capsules. Pull seat belt out all the way and then let it retract to disengage.

Hi, these retractors or sensitive to direction so that if the are not sitting properly they will not release. as if in a roll over situation. try holding the retractor at the angle at which it was mounted and then apply slight tension on the belt pulling out. Don't take the plastic covers off or the spring inside will come a part and you will be buying new belt assembly's

Hi,I am guessing you haven't used these belts for a while.Quite often they will wind themselves up with normal car movement and lock.Grab the belt and pull as hard as you can(stretch it).It should come free.

you need to pull the belt out all the way to release it ,they have a locking mechanism for baby seats that stops them retracting,you pull them all the way out and they are reset and retract,common in modern cars,rare to give trouble

make sure that the rear seats are properly locked into rear catches as this can stop your seatbels from working if ok then sounds like your seatbelt is faulty req new seatbelt.

1)move the plastic cover over the seat belt out of the way to gain access to the two mounting bolts for the seat belt mechanism. Use a 10mm wrench and a 14mm wrench and remove the two bolts holding the seat belt mechanism to the body. Use a small drill bit or small screwdriver and make one hole in the plastic cover on each side of the seat belt mechanism (the covers say "do not remove plastic cover". Spray lots of wd40 in each hole. Then exercise the seat belt. When the mechanism allows the belt to be retracted, retract the belt all the way out and exercise the seat belt. Reinstall mechanism with both mounting screws in original position and put plastic cover back in place. Good luck. New seat belt costs $100.00 from dealer and are hard to find working in junk yards. I have fixed several of them this way.

If it is a 850 sedan like mine then you'll have to remove the speaker covers and then pull up the rear deck cover, then you can get to the mechanism.