Driver's Seat belt problem

Car is 1998 Mk 2 and I had the same problem before. I purchased a second-hand replacement and all was well for a year or so. Now it is happening again. Sometimes when joining a main road and I want to lean forward to see if anything is coming it will not release. I have to do carefully judged jerks to get it free. I am fortunate in having another car so the MX-5 lives in the garage and comes out occasionally on nice days.

I am a careful DIY person who will take on most things. I have contemplated taking apart my first seat belt to see what is wrong. The green side seems to contain the restricting mechanism. I note there is an electrical connector that presumably operates the tensioner and that is on the red side. If I remove the green cover, figure out how it works, figure out how to fix it will I stand a chance of success? The green cover has, “Caution, do not remove” written on it.

Just a thought…  Are you on a slope when this happens?  Or still slowing down? 

Remember the mechanism involves a pendulum lock as well as the centrifugal lock and it will grab if it thinks there is a deceleration in any direction. 

Also, more worryingly, is the reel mechanism not level in the car and tilted somehow, eg rust allowing its mounting to bend?


It happens when I am stationary. I get in and try to pull out enough seat belt to put around me and secure. But often it locks before I have enough belt. So I stop pulling, and then very gently pull again. And nothing feels as if it is bending.
The seat belt I took off a couple of years ago is on my desk. And it will only let the belt release for about an inch, however gently I pull. I appreciate that the angle is important, but I have tried every angle.
As other people don’t seem to be having my problem I realise that I may be doing something wrong, but if so I don’t know what.
Any suggestions appreciated. A new one is about £152 I think so fixing the one I have would be good.

Hmm, I assume it does not have a pre-tensioner (there would be a connector and an SRS warning sticker). If it did and the charge had gone off then a new belt would be needed.

The tilt angle for pendulum locking is at about 30 degrees. Much more or less then there is a problem, new belt needed.

The centrifugal locking might be pre-settable if you can coax the whole of the belt out, and then slowly let it back in while the ratchet goes click click click. No clicks even after cycling the belt a couple of times, then there is a problem, new belt needed.

If you take it apart there is a mega spring inside that cannot be rewound by hand, new belt needed, possibly also fingers and/or plasters.  However, you might be able to remove a cover and clean out (use brake cleaner) greasy crud that is jamming the delicate mechanism (some fool might have used WD40 on it), BUT BE VERY, VERY CAREFUL and aim it all away from you (and any onlookers).

A second hand belt might well have the same problem.  Check also that if it has an arrow on it that this faces forwards.

Good luck, and BE VERY CAREFUL.

Thank you for your detailed and informative answer. I think I have a pretensioner because there is an electrical connector and a sticker saying ‘danger’ in several languages. I imagine it would be apparent if the charge had gone off and there are no signs of that. I have now coaxed the belt to full extension 3 times as you suggested, and it is no better. The passenger belt works perfectly presumably because of less use. (My wife is reluctant to travel in the MX-5.)
I was amused and suitably warned about a spring bursting out. I have encountered that before in other devices and spent a ridiculous length of time trying to persuade them back into position, so I will take your warning very seriously. The driver’s belt in the car is useable with patience. In the mean time I had hoped to make the one on my desk work by understanding the problem and putting it right. It looks like this
and as a new one is about 8 times more expensive than a second-hand one I think the message is clear.
But if I can pick your brains some more I think I can just make out the spring under the red cover. Also there is a ‘danger’ sticker on the red side. So I wouldn’t want to touch that.
But the green cover is semi-transparent and I can see some sort of mechanism operating. We all know that if you pull on a seat belt sharply it locks and if you pull slowly it releases so that you can put it round you. Well, I think it is that mechanism that is not permitting a slow release and I think I can see it under the green cover. I am considering taking precautions, (eye protection, gloves, no bare skin etc) and removing the green cover and perhaps cleaning up, as you suggest. Sorry about so many words, but what do you think?

It is your risk if you take it apart! 

Myself, I would simply replace it with a new one - my life, my safety.

The pyrotechnic should not go off if there is no voltage around the terminals, but the detonator is quite sensitive so CARE is the watchword.  If it does go off it will become burning hot; in theory the flame itself is contained within the metalwork, and by the time it escapes to the outside air it should no longer be flammable, but it will all be too hot to touch and there could be some nasty chemicals left over.  Put a shorting link across the plug contacts to prevent any static electricity having a chance of triggering it (it shouldn’t, but Murphy’s Law applies here, or as Terry Pratchett’s characters were fond of saying ‘the one in a million chance is the one that always happens’.)

If you can see the ratchet mech, then you stand a chance of cleaning it.  Don’t use anything that is flammable or might dissolve plastics.

Good luck and be careful.


Forgive my intrusion and ignorance, as a worst case can the seat belt units be swapped from passenger side to driver side (and vice versa) so as to remove the issue from the driver? It would seem to suggest this in the link to the replacement part.

Just a (silly?) suggestion that might work until you can hopefully fix the faulty unit.

I took careful note of the warnings and have a satisfactory result so far. The car has done two journeys and the seat belt has behaved perfectly. And of course, if you pull on it sharply it locks as it should.

As explained I had a seat belt in front of me that I had removed from the car a couple of years previously. Annoyingly the present seat belt on the car was exhibiting the same fault.

Clearly the ‘big spring’ is under the red cover and the pyrotechnic is on the same side so take care of that side and leave it alone.

The semi-transparent green cover can be carefully removed by levering near the 3 fixing points. (I used a medium and small screwdriver in combination.) I was able to do this without damaging the fixing points and later the cover was securely replaced.

When the green cover is removed nothing flies off or even falls off.

Once exposed it is apparent that when stationary the unit must be vertical otherwise a mechanism at bottom right causes a plastic flap to engage with the black ratchet wheel preventing the belt from releasing. (The mechanism can be temporarily removed by sliding it relative to the metal mounting plate.)

I tried to take apart the centrifugal mechanism by carefully prising up the central metal spindle. I failed but then retested the belt release and it released smoothly full length every time. So I don’t know if my efforts loosened the mechanism or particles of dirt fell out. I blew repeatedly on it but used no cleaning fluid. Replacing the green cover was easy.

For an amateur like me there is quite a lot of labour in replacing everything properly, particularly the shaped trim that covers the whole seat belt unit. Unfastening the electrical connector was challenging. The springy yellow plastic clip visible centrally in the top of the plug must be pressed away from the white plastic. But this does not release plug from socket. It allows the combined plug and socket to be pushed downwards releasing the combination from the metal wall. Once the combination is freed the plug can be released from the socket by raising a pivoting clip of white plastic on the socket. It must come up a long way before the plug is freed.