Toyota Hilux inertia seat belts wont work

Strange how they work o.k off car and new belts do the same .The only time I have had a similar prob. was when the belt was not mounted level .

Hi whittingehame, yes over the years fitted lots of seat belts and there is nothing I have not done to a car,but these belts have got the better of me, the inertia mounting can only go on one way ,it slots into a hole and is bolted down,it is impossible to fit wrong or to get them mixed up by putting on the wrong sides,they are not like the old ones ,as you said (not level ) had that problem in the past with the ball bearing,I have tried everything, a very simple job ,I can hold at any angle even upside down and pull and they work great every time,(off the car ) put them on the car (very slackly fitted they dont work,tighten down a bit more ,dont work,tighten tight dont work,take them off !! they work ,Have tried and tried,will have to by a different model belt,this is the only job on a car that has beaten me ,thanks for your reply