fredd1

FYI for those C4 owners with locked up seat belts:


Full assembly with the cover removed.


Close-up of the lap belt locking & cinching mechanism


Close-up of the shoulder belt locking mechanism




The top picture is the locked belt assembly as received. The locking mechanism for the lap belt is essentially a weighted pendulum (1) which hangs vertically down off a stationary red plastic bracket when the assembly is properly mounted and oriented. Any deceleration or impact will cause the pendulum to rotate engaging the black plastic pivoting arm (2) and lever which in turn engages the red plastic lever/pawl (3) and metal pawl via the black extension of the pivot arm (the other end of this black pivoting arm also engages the shoulder belt pawls). When this red levered/pawl pivots it engages a tooth in both the red ratchet (4)attached to the lap belt spool axel and (under more extreme rotation) the adjacent metal ratchet causing the axel to lock-up. The metal pawl and ratchet appear to be mainly engaged with the chinch lever and heavy deceleration while the additional plastic pawl which engages the red plastic ratchet just outboard of the metal ratchet is engaged under the more moderate deceleration of a breaking. The metal pawl is only loosely attached to the red plastic lever via a slotted opening, and appears to be a redundant element actuated by the cinching plunger or under these more extreme stopping conditions (?).

Under normal driving conditions, when the pendulum returns to its' normal vertical rest position the black pivot arm extension is allowed to move back out of the way and the red lever/pawl (and/or metal bar pawl -note there are no return springs, gravity pivots and unlocks these pawls) is allowed to rotate back out of the ratchet tooth and the belt can then be pulled out (assuming the cinching mechanism has not been engaged). The mechanism as received was locked because the red lever was stuck in the locked position (pawl engaging the ratchet tooth) even when the assembly and pendulum were properly oriented. I manually disengaged the red lever/pawl from the ratchet and was able to pull the lap belt out easily. After working this lever back and forth a few times and cleaning up the assembly a bit, the belt was working as expected (e.g.. locking the belt spool when the pendulum was more than about 15 degrees off vertical, and releasing when in its' vertical rest position). Cycling the shoulder lever/pawls released those also. From what I can tell, there was nothing broken, just the levered pawls binding up due to dirt and rust. It should be emphasized that the lap and shoulder belts are only free to extend when the assembly is oriented in the vertical position, so if you have one laying flat on a bench they will appear to be locked-up since the pendulum is not hanging vertically down.

I can't categorically say that binding due to dirt and rust are the only cause of the seat belt locking (damage to the plastic elements in this mechanism are also a possibility), but it seems to be the likely cause in many cases contrary to what was stated in the 1991 recall notice:

"The retractor lock-up problem can occur only if you attempt to fasten the safety belt while either accelerating, braking, or bouncing over a rough road so that the retractor attempts to lock-up as it would in a vehicle crash. If this condition occurs and you have just started to pull the belt out of the retractor (first six inches of belt travel) you will feel resistance as the retractor attempts to lock-up. Continuing to pull on the belt in spite of feeling this resistance may break the retractor and you would not be able to use the safety belt."

Note the recall notice excerpt above states this is the ONLY way lock-ups can occur which doesn't seem to be the case.

For anyone having this lock-up problem, opening the case, cleaning, and freeing up these pawls may do the trick.There is also a small hole in the case adjacent to the pendulum which might provide enough access to unlock the mechanism without even un-mounting and opening the case. In any event opening the case is fairly simple process since the two halves are only locked together by 8 molded plastic tabs on one half which snap into slots in the other half of the case. Remember though that these are government mandated safety components and YMMV-DAYOR.

Addendum:
After pulling apart yet another seat belt assembly, one that was also locked, I have to revise my evaluation of the main cause of the lock-up a bit. I found that this one had a broken or very weak spool retractor spring on the shoulder belt spooler. If the belt retracting spring action isn't sufficient to retract the belt and reverse the spool sprockets' rotation, the pawl will stay engaged in the sprocket causing the lock-up. It seems that gravity alone is not always enough to disengage the pawl particularly if there is some binding at the pawl supports due to corrosion or dirt. So if you release the pawl manually and the belt still won't retract, the spring is most likely broken or too weak to overcome the friction between the sprocket tooth and the pawl and/or the internal resistance in the spool mechanism. Replacing the retractor spring will be necessary in this case.

-Fred

LongBeachC4

Mine is doing the opposite, it won't catch when pulled hard.

fredd1

The top of the pendulum is slightly domed and there is a caming action as it rotates which forces the black pivoting lever (#2) to engage the pawl locking into the ratchet. It sounds like your pendulum either isn't rotating or the plastic pawls are broken. You might try poking around through the hole in the case to see if you can loosen up the pendulum. If you can rotate it out of its' normal vertical position and the belts still don't lock you probably have some broken elements in the mechanism. Again it's the inertia of the pendulum under acceleration/deceleration that activates the locking mechanism, not the rotational velocity of the reel, which would be the case in an inertial reel where centrfugal forces provide the actuation mechanism.

fredd1

Addendum:
After pulling apart yet another seat belt assembly, one that was also locked, I have to revise my evaluation of the main cause of the lock-up a bit. I found that this one had a broken or very weak spool retractor spring on the shoulder belt spooler. If the belt retracting spring action isn't sufficient to retract the belt and reverse the spool sprockets' rotation, the pawl will stay engaged in the sprocket causing the lock-up. It seems that gravity alone is not always enough to disengage the pawl particularly if there is some binding at the pawl supports due to corrosion or dirt. So if you release the pawl manually and the belt still won't retract, the spring is most likely broken or too weak to overcome the friction between the sprocket tooth and the pawl and/or the internal resistance in the spool mechanism. Replacing the retractor spring will be necessary in this case.

rocco16

At certain times, I'd like to be able to manually lock up the shoulder strap as well as the lap belt.
Any way I can make the unit do this??

fredd1

AFAIK, not with the stock seat belt cinching mechanism. You might be able to modify the stock unit to manually engage/disengage the shoulder pawl, but I think you'd be better off installing a 4-point harness...

helphos

Another cause of seat belt jamming is this: Sometimes the plastic cover of the seatbelt mechanism gets damaged where the seat belt pulls through. It's supposed to keep the lap belt aligned on the reel when it's released and retracted on the reel. I recently replaced a seat belt assembly that the lap belt had gotten jammed on the ratchet mechanism on the side of the reel. The belt was partially wrapped around the ratchet and wouldnt rewind and wouldnt come farther out.

What had happened was the plastic cover has a slot for the belt that keeps it properly aligned to the reel, and over time the plastic had worn thin and finally broke, no longer maintaining the proper alignment and allowing the belt to get caught on the ratchet.

Lesson: Keep an eye on that plastic cover, and try to help the seat belt slide properly back onto its reel when you unbuckle your seatbelt to prevent wear on the plastic cover or misalignment of your belt when it retracts.
i discovered this when i was installing a replacement belt to solve my jamming problem.
Good luck!

shakedown067

Nope, you'd need to get one like this from Corbeau.

abenton

1987 c4 should have left it alone?? my belt would cinch on occasion after a bump or corner, only way to release it was retract it all the way then pull it back out.. thought the clean and oil my cure the problem but noooooo,,, made it worse or i'm missing the obvious x2, opened it up found 7cents change and dust ***** cleaned and oiled reinstalled NOW won't come out at all,, apart again manually released OK reinstalled NOGO again,,, bought used working model when guy took it from vette carcass, brought it home installed it NOGO, locked up same as mine,,, SEEMS something comes loose locking it in racheted position and I can't tell what it is,,, any help would be awesome!!!! I should have left it alone

jv9999

In my '87 I tried most everything and finally found the coil spring on the side needed a little more tension. A little bend of the L shaped end fixed it.

Having said that, I don't recommend anyone try to fix a seatbelt, it should be replaced...

MaxDaemon

FWIW - my "new" '84 had a locked passenger seatbelt when I bought it. It wasn't until my wife tried to use the seat belt we found out. I discovered after some trial and error (hotel parking lot, no tools to speak of) that I could stick a screwdriver into the belt opening and slowly roll the seat belt back into the casing. Once the belt was fully retracted, it released the mechanism and I was able to use the belt normally again. Of course, this might just be fluke and only worked for me.

I'll be talking to my dealer on Monday about a replacement - anyone know if they're still honoring the free recall?

VikingTrad3r

i have an 87 and the passenger side upper retract (for the shoulder belt) will not retract once its been pulled out. the lap belt will retract, but shoulder will not.

stiej

For me my passenger lap belt was locked. It took it apart and gave it a vacuum and sprayed some plusgas on the plastic parts but more to the point found that the metal pawl was always falling into the teeth of the ratchet. It seemed because the metal spring ( more like a folded piece of metal folded almost into the shape of a question mark) which rests against the belt fabric seemed to not be pushing the metal pawl away from the ratchet enough. So I gently forced the spring back away from the pawl to breathe some more life into it and that did the job. The system still locks up as it should when tilted.

Pa'svette

There is a safety recall on Corvette seat belts and GM will replace them. The dealer has wanted to replace them on my 91 but they only had black ones. Mine are grey and work fine so I haven't done it. The factory rep. told me that safety recalls never expire. Don't know what year you have but may want to check with a GM dealer.

Bob

stiej

Well I'm in the UK and my 87 is imported and I'm the 11th owner so not sure how I stand when it comes to recalls?!. Something I should look into though. Thanks.

However, what's the difference in the replacement units? Are they resilient to locking up due to a revised design or something?

ghoastrider1

A word of warning. If you are going to remove the belt assy yourself, use a impack. Do not use a a breaker bar or a rachet. There is a good chance you will strip the bolt, espc the one on the tranny tunnel.

stiej

Thanks. What's an impack. And what's the problem/why can't you use a ratchet or breaker bar? Is the metal the threads are made from rubbish?

2ooo-C5

My upper seat belt will not catch.
When I go to an HPDE they jerk out on the seat belt to make sure it locks.
If it wont, you don't pass inspection.

Is something broken, or does the car have to be in motion for the catch to work.
This thread made it sound like the car needed to be stopping hard to make it catch.

Engine MR

Great read... I followed the above and after a couple of tries I had succes. My hip belt was sometimes locking when trying to buckle up. Thanks for the effort of making this How To.

ghoastrider1

happened to mine too..its a common problem with out older c-4s. I went on e bay and bought new ones. If you go this route,,CAution, USE AN IMPACT TO LOOSEN the mounting bolts. They are very tight and using a breaker bar jst might round off the bolts. best of luck. btw, mine happened b4 fix was posted.