I seem to have displeased the Volvo gods and have lately been experiencing
some of the typical 850 failures: First glove-box stuck closed and
now driver's-side seat-belt retracts but won't release. I was able to spool
out my seat-belt by removing the plastic trim cover, and fiddling with the
spindle, and then keeping a large paper-clip on it to prevent it retracting,
but obviously not a great solution.

My friend-with-a-lift down the road suggested the mechanism was probably
just crudded up with dust and hair, so we went at it with compressed air
last night, but in fact only made the problem worse. Frustration led to
a "what the heck" attitude, so we took the thing apart (it was already
busted!).

The lower unit mount of the spindle is covered in sticky foam, and removing
that exposed some break-off clips holding the two halves of the casing
together. Broke those, and at the front of the unit (steering-wheel side)
was a brass weight held in a small plastic cage. This is designed to
rock from side-to-side when the car decelerates and lock the ratchet. The
small plastic cage was very microscopically deformed, and we could see that
it was engaging the ratchet most of the time. Basically, just ripped that
part right out, and the seat-belt was functioning again. The ratchet still
locks when you pull firmly on the belt (as would happen in a sudden stop),
and of course the pyro device is still there in case of a collision, so we
didn't loose all the safety features of the belt, just the little pendulum
mechanism that locks the ratchet when the car is decelerating even in the
absence of belt-pull. I'd say this was a win, as now my seat-belt is
properly adjusted when driving (not held in place by a paper-clip).

Coincidentally, a neighbour's recently purchased junker third-row seat
setup had a frozen belt (was fully retracted and wouldn't release). In
this case, someone had let the belt fully retract after removal from the
junker, and then tipped the unit over which engaged the little pendulum
weight locking the ratchet. As the only way to release the ratchet is
to retract the belt a 1/4 turn, this was now frozen. Taking the thing
apart (can be done non-destructively as the clips on this unit are not
break-off style), we were able to release the ratchet, re-assemble and
it was as good as new.

Bottom line: These pendulum mechanisms are delicate, lots of plastic,
and vulnerable to dirt and probably even warpage due to heat or just
plain age. Dis-assembly and cleaning can solve the problem, or failing
that, removal of the little brass ball (seat-belt castration!) will get
you going again.

For those whose belts won't retract, there is a spring mechanism on the top
unit mount of the spindle. If the spring is broken, you're out of luck, but
if it just slipped out of the spindle, this can be fixed by removing the unit,
locating the end of the spring, inserting it back into the slot at the top
of the spindle, and rotating a few turns to pre-tension and re-assemble.

Just thought I'd pass on the experience. The consensus on this board and
others is that you can't repair the seat-belt mechanism when they fail,
and given the amount of fragile plastic parts in there, I'd say that from
a liability point of view, yes they need to be replaced. But, at your own
risk, go ahead and try the above if you want to restore operation of your
failed seat-belt.

Good luck.

grant..