seat belt retractors use a balance weight or steel ball bearing in a see-saw switch type lock. to lock the belt. the idea being that when the car stops suddenly the weight or the ball bearing moves off centre and locks the belt to stop you hitting the dash
regardless of how slow or fast the belt is pulled from the retractor
these are very sensitive.
along with that, a retractor is specified for a maximum length of belt. which equates to roll tickness on the reel when the belt is extended up the pillar to the top loop and back down to the anchor in the sill.
if that distance changes or the belt is re webbed with a differeent thickenss of webbing they can bind..... BUT
i'll go with the first issue as it is most likley
if the belt retractor position varies by more than a few degrees off the level front to rear or side to side the locking actuator is already biased towards locked and will be either locked or very...tooo toooooo sensative to being locked by the rotation of the retractor.
In fact the retractor has a part of it that drives a nearly locked belt to be totally locked if it so much as catches. this is either designed in by the shape of the lock teeth or there is a fly-out weight. the only brand that dosn't do this is Kangol Reflex you can NOT lock one of them with a very fast pull... hence people (Jaguar/trumph) think their expensive belts are broken....
On a car that had fixed belts there was no reason to get the belt mounting position directly upright. it can be into the curved base of the B pillar. you need a spacer to avoid the retractor from leaning back into the pillar.
on a car that has been messed with the retractor may well be missing the spacer that fits between it and the sill of the car at the mount
in both these cases the belt retractor leans back a few degrees and the problem is as you find... the belt locks up
the other issue would be easier to fix and that is the belt retractor leaning forward or back.
straghten it up to get the best belt action on flat ground with the car at your designed front/rear ride height.
last but not least...Really high end belts sometimes had an angle adjuster
this allowed the switch/weight housing to be set upright even if the reel housing was off in one direction or another..... supposed to be used to convert belt retractors from front seat B pillar mount to rear seat parcel shelf or boot floor behind seat mounting. You are unlikley to come across these very often as most people just buy the correct style belt for the job.
belt mounting hardware is more or less standard USA/Europe/SA/Australia/NZ
some chevys and porsche used metric i think...?
the retractor hard mounts to the sill. sill---> flat spacer---retractor tab----spring washer---> head of bolt.
the bottom anchor of the belt is usually a second hole in the sill
sill---> profiled spacer to allow swivel of anchor tab----> anchor tab----> spring washer, that presses only on the spacer not the anchor tab----> head of bolt
the top mount is mounted in a similar way. metal loop on an anchor that uses a spacer to allow swivel or a drop link in a coupe/hardtop/2 door/fastback with a belt loop on its end
like this
SET OF 2 Seat Belt Drop Links for coupe and two door vehicles. - Seatbelt King
thse come with loops big enough to allow a buckle/clasp tongue from most belts to pass through so you can change the neck chopping set in your 2 door into a safe over shoulder belt by usuing the drop link .
luckily standards are equivelent across US canda Europe Australia
In summary
the belts need to be correctly mounted before any appriasal of an issue with the retractor can be made, becasue a badly mounted belt is biased into a near locking state and doesn't work properly, it locks up all the time when pulled.
and obviously everything mentioned above means you can not test a belt easily off the car unless you bolt it dead upright onto a bit of steel in a vice
Dave
