It's a common complaint and one that smart addressed in 2010. The seat belts retract, slowly, if at all.
You have to start manually feeding it back so it doesn't hang out the door and get damaged.
The initial reaction is that the seat belt spring in the reel is too weak, however, that's not the case.
The angle and shape of the original guide is the issue here. Here's why. Here comes the science.
Look at the original seat belt guide (below). The slot that the belt passes through is curved, this is to try and give
a decent angle when the belt is worn and when it's not. The shape is a trade off and doesn't really work that well.
When the seat belt isn't being worn, the webbing is curved a lot more than when you are wearing the seat belt.
This curve increases friction over the webbing to the point where the spring in the reel can't retract the belt.
The change of angle as it passes through the B pillar guide to the seat guide doesn't help matters either.
You can see it goes from vertical to horizontal over a few inches behind the guide.
In 2010, after many complaints of faulty seat belt reels, smart redesigned the belt guide on the seat. (See below).
The aperture that the belt passes through is flat to reduce friction and the unit rotates to adjust
to the angle of the belt if it's being worn or if it's at rest and hanging straight down.
These 2 factors reduced the friction enough so that the belts retract correctly.
I know! If you have the old style seat belt guides then you are still going to suffer with non retracting belts.
If only there was a way to swap the belt guides over from the old style to the better new style rotating ones.
It wasn't long after they changed the style that I got an email from Bryan M saying he had changed them. His photos
and explanation weren't the greatest so I bought a pair of guides and then did nothing with them for 3 years!
In March 2014 I had an email about poorly retracting seat belts so took them
out of the parts box, dusted them off and did a guide for swapping them over.
Look at the fixing points between the 2, they are the same. How hard can it be!