A diagram for the non believers:

For the non-engineers, this is a free-body diagram. What you do is show all the forces on a point. The forces must be equal and opposite (ie all cancel out) to keep the object balanced.



As Doc says, the sill sees the force.

Whether it is an inertia reel system or fixed belt makes no difference. It is the mounting loactions of the ends of the belt that makes the difference. If the belt ins anchored at the top only then the force at the mount is less than if the belt goes around that mount then down to the floor.

M

The ACT registration authorities once defected inertia belts fitted to pre-Clubman minis and the "pulley theory" may the reason why. Interestingly, I understand they have now relaxed this ruling. So, my question is - are the B pillar top mounts stronger in the Clubmans (the ones fitted with factory interia reels) than in the earlier cars?

_________________
1967 Cooper S - new front bearings to do.
1965 Cooper S shell - Slow progress. No time or money!
1966 Deluxe- next rustoration!
Mk 2 & XJ6 Jags. Less said the better.

Right, now we're getting somewhere...

However....this diagram doesn't take into effect the fact that the buckle in the centre is also acting as a pulley. That needs to be factored in as the entire belt system is just that, a system. You can't consider any single point in isolation.

Also, I'm not convinved about that downward arrow from the B pillar....I'm beginning to think that yes the 'lapward' force plus the downward force will add to be the force of the anchor point...but I'm thinking they may simply equal the force that was on the point in the first place...

Once the inertia part is locked, it will then act as a static lap sash, wouldn't it?

No Wil, it won't.

It is topics such as this one that serve to highlight the issues engineers face.

Most people believe they can understand all mechanical concepts where they are happy to concede a lack of knowledge on chemistry and electronics.

The fact is that, while many mechanical topics are intuitive and many people can understand them without training, many are not.

Please do not underestimate the value of high school physics followed by 4 more years of training.

smac may not be convinced by my diagram but I can assure him that there is a simple force balance at the top mount that can be assessed without showing all of the rest of the system.

I'm beginning to wish I hadn't questioned the logic. All food for thought though. Makes interesting reading and gets the grey matter working.
I'm still keeping the inertia reel belts in Morris.
If we're talking about an accident that has enough force to collapse the "B" pillar think of the damage an old static belt will due to your internals in the same accident....???
Its a matter of the lessor of two evils me thinks.

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Mokesta is right about the forces, but whats got me worried is I have a 1963 850 and its had inertia reel seat belts put in the front, now this was done by the previous owner and it has a compliance plate for it.
Now my question is this safe :S im getting real worried that my B pillar will implode if I get in a crash...

This has been a long thread compared to many others and highly thought provoking.



Thats a difficult question, I guess we are all trying to say dont fit them in preference to fixed mounted style belts but if they are in then so much the worry.

In the event of a major survivable accident, the B piller may come towards you but I doubt it will implode as such. The B piller was always a significant structural and load carrying item. It just wasn't designed for an inertia reel belt. Having said that, I bet the B piller in a clubby etc is made to meet the standard and no more than exactly that.

Toss a coin ??? Sounds flippant I know, but who will say for sure with confidence.

So what year approx did the reinfocred pillars enter production? Can you tell the difference betwwn a reinfocred one and an early non reinfocred one by looking at it? I have a 68 and it looks to be double skinned where the top mount is.

Morris 1100 would know
Anyway, I'll be keeping my retractables in the '69 S and take my chances.
I've done a lot more stupid & risky things in my time

_________________
1967 Cooper S - new front bearings to do.
1965 Cooper S shell - Slow progress. No time or money!
1966 Deluxe- next rustoration!
Mk 2 & XJ6 Jags. Less said the better.

The reinforced B pillers came with the burst proof door locks - if you have an old style flatish door catch on the B piller then its the old type.

The new type has a semi circular steel ring on the B piller. Such as on a clubman.

I have a body repair manual from late 68 and it shows a change to the pillars from Mini 850 body number 39562. This may have just been the introduction of seat belts. This was done before the Deluxe and Cooper S were in Australian production.
The next change that I know of was the change to burst proof door locks (ie: lift up door handles)

Mick
Those changes you mention on the B piller from 850 body number XXXXX on are fairly well known. Its a bit of a curve where the door striker is that was indroduced.

You notice it where a Cooper S replica has been created (re-shelled) using the lighter 850 shell, or where an 850 shell has had wind up window doors fitted. The doors just dont close evenly. They hit on the piller as they contact the striker.

So in saying that - sliding windowed doors fitted to a Deluxe/Matic will have plenty of clearance from door to striker?

Dont know willy - never ever tried it that way.