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Author: Subject: Upper seatbelt mounts
Stuart Walker

posted on 30/4/19 at 05:54 PM Reply With Quote
Upper seatbelt mounts

Hi all,

After a few years away from the car I'm now back and having a great time sorting it out. One of the original SVA fails was on the upper seatbelt mounts. Looking at them now they are clearly no good as they are, so I'm considering the best way to improve them and would be interested in what anyone else has done.

The current situation is little box section stumps welded to the horizontal chassis rail behind the seats, with captive nuts welded inside each stump. My plan is to get rid of the captive nuts and use longer bushes instead, but I'm wondering whether to go through the existing stumps and the horizontal chassis rail, or whether to weld the bushes behind the stumps. In either case I reckon I will go for long bushes (is this still the right term when they are this long?!) and also weld them onto brackets on the diagonal chassis rail.

I will also, as recommended by the original assessor, triangulate the stumps with some box section angles back to the chassis rail behind. My questions for anyone who might've been in a similar situation are...

Are the long bushes down to the diagonal rail worth doing?
Through the stumps or behind the stumps?

I've made some pictures in a CAD program called Publisher which hopefully shows what I'm on about. I guess I'm probably looking at 1 or 1+3 hybrid, but open to suggestions! Blue /green is current, red is new

Any thoughts?

Cheers

PS. No need to tell me how stupid the original version was, I'm well aware


[img]seat beltmounts_april19 by Stuart Walker, on Flickr[/img]

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Stuart Walker

posted on 30/4/19 at 06:59 PM Reply With Quote
Should also have said - I've got two roll bars (the cobra style ones) hence the extra plate on top of the chassis rails, but can't do the roll bar seatbelt mountings.
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Mr Whippy

posted on 1/5/19 at 05:15 AM Reply With Quote
Is this how it looks?

Personally I'd weld a new bar between in the inside of the hoops and fix the belt to that...it will be vastly stronger than your other suggestions


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pewe

posted on 1/5/19 at 09:41 AM Reply With Quote
Mine used the vertical towers with angled braces back to the horizontal rail behind - similar to your top right but without the verticals below the towers.
I worked on the basis that manufacturers use relatively light weight mounts into thin steel for their seat belt anchorages and those will have been worked out scientifically - we hope!
The sst involved will be more than capable of retaining a human.
All rather unscientific I know but reckon it's over- engineered for the job.
HTH.
Cheers, Pewe10

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nick205

posted on 1/5/19 at 09:59 AM Reply With Quote
These were the upper harness mounts on my MK Indy, which passed the SVA without any issue...


MK Indy harness fixing point 2
MK Indy harness fixing point 2




[Edited on 1/5/19 by nick205]

[Edited on 1/5/19 by nick205]

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Angel Acevedo

posted on 1/5/19 at 11:05 PM Reply With Quote
I don´t think thr long bushes are doing any work at all.
Most of the load on the Shoulder Harnesses will be tension on the rear-front direction.
The inclined part may be replaced with flat bar and wrapped around the rear horizontal member to increase weld area.
A hole the same size as the mounting bolt would be enough as it will see only tension onte aft-fore direction as above.
All loads (or most of them) on the Down-up (Or Up-Down) for that matter will be taken by the lap belt and the crotch straps -if installed.
My uneducated opinion only.
Regards
AA





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40inches

posted on 2/5/19 at 08:29 AM Reply With Quote
quote:
Originally posted by nick205
These were the upper harness mounts on my MK Indy, which passed the SVA without any issue...


MK Indy harness fixing point 2
MK Indy harness fixing point 2





Mine same as Nicks, but I took the strengthening bracket from underneath the box section.
The examiners at the Nottingham IVA centre paid particular attention to the rear belts mounts, and said this type of fitment was fine.

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Stuart Walker

posted on 2/5/19 at 09:05 AM Reply With Quote
Thanks all. Hopefully get it sorted this weekend - that will be one of the major jobs out of the way

I couldn't see your picture Mr Whippy, but I have tried to avoid involving the roll bars as if I did I think I would need to modify where the hoops meet the chassis in the middle - at the moment they are welded to a plate welded across the two horizontal rails. I thought I might end up making myself more work (i.e. having to add more verticals), but I see your point and will give it some thought. I can't picture what support there is below that horizontal rail without looking at the car.

Thanks pewe - I might go for something like that. I assume you used bushes inside the box section?

AA I agree they don't add much, though maybe the whole thing might pivot at the top chassis rail in the event of an accident and perhaps the lower fixings could prevent that?

And thanks Nick / 40inches - great to see some finished and successful versions!

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40inches

posted on 2/5/19 at 09:07 AM Reply With Quote
quote:
Originally posted by Stuart Walker
Thanks all. Hopefully get it sorted this weekend - that will be one of the major jobs out of the way

I couldn't see your picture Mr Whippy, but I have tried to avoid involving the roll bars as if I did I think I would need to modify where the hoops meet the chassis in the middle - at the moment they are welded to a plate welded across the two horizontal rails. I thought I might end up making myself more work (i.e. having to add more verticals), but I see your point and will give it some thought. I can't picture what support there is below that horizontal rail without looking at the car.

Thanks pewe - I might go for something like that. I assume you used bushes inside the box section?

AA I agree they don't add much, though maybe the whole thing might pivot at the top chassis rail in the event of an accident and perhaps the lower fixings could prevent that?

And thanks Nick / 40inches - great to see some finished and successful versions!


If you want to nosey round a finished car, you are welcome to pop over. Don't think you will be that far away?

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Stuart Walker

posted on 2/5/19 at 10:20 AM Reply With Quote
Thanks that would be great! I work in Chesterfield and Derby a lot so definitely not far away.
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40inches

posted on 2/5/19 at 10:33 AM Reply With Quote
quote:
Originally posted by Stuart Walker
Thanks that would be great! I work in Chesterfield and Derby a lot so definitely not far away.

I'm retired so in most of the time, U2U when you want to come over.
I'm 3 miles from J30/ 2 miles south of Crystal Peaks.

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Angel Acevedo

posted on 2/5/19 at 04:19 PM Reply With Quote
quote:
Originally posted by Stuart Walker

AA I agree they don't add much, though maybe the whole thing might pivot at the top chassis rail in the event of an accident and perhaps the lower fixings could prevent that?



I reckon the strap would weight a lot less than the lower fixings.
But it will be your body strapped to those, so if you feel safer with your method, I´m in no position to argue against it.






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Stuart Walker

posted on 3/5/19 at 10:18 AM Reply With Quote
Fair point on both counts

Thanks 40inches, once I'm fully immersed in the build again I would love to come out and have a look at yours one day - thanks, I'll be in touch.

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Mr Whippy

posted on 3/5/19 at 11:14 AM Reply With Quote
I always keep this in mind when doing belt fittings -

In a 30mph collision, an unbuckled backseat passenger will hit the front seats with a force of around 30 times their body weight, which could equal the weight of a small elephant.

The forces involved in crashes are huge. I had a 30mph head on crash once and had a perfect bruise of the seatbelt right across my chest. Worked with a guy who ran into the side of a lorry at 70mph and his belt actually broke and collapsed shorty after from a punctured lung. I lift engines out using seatbelts...

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Stuart Walker

posted on 3/5/19 at 12:55 PM Reply With Quote
Thanks Mr Whippy, certainly a job to take time over and get right. Cheers
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907

posted on 5/5/19 at 06:29 AM Reply With Quote
quote:
Originally posted by Stuart Walker
Hi all,

After a few years away from the car I'm now back and having a great time sorting it out. One of the original SVA fails was on the upper seatbelt mounts. Looking at them now they are clearly no good as they are, so I'm considering the best way to improve them and would be interested in what anyone else has done.

The current situation is little box section stumps welded to the horizontal chassis rail behind the seats, with captive nuts welded inside each stump. My plan is to get rid of the captive nuts and use longer bushes instead, but I'm wondering whether to go through the existing stumps and the horizontal chassis rail, or whether to weld the bushes behind the stumps. In either case I reckon I will go for long bushes (is this still the right term when they are this long?!) and also weld them onto brackets on the diagonal chassis rail.

I will also, as recommended by the original assessor, triangulate the stumps with some box section angles back to the chassis rail behind. My questions for anyone who might've been in a similar situation are...

Are the long bushes down to the diagonal rail worth doing?
Through the stumps or behind the stumps?

I've made some pictures in a CAD program called Publisher which hopefully shows what I'm on about. I guess I'm probably looking at 1 or 1+3 hybrid, but open to suggestions! Blue /green is current, red is new

Any thoughts?

Cheers

PS. No need to tell me how stupid the original version was, I'm well aware


[img]seat beltmounts_april19 by Stuart Walker, on Flickr[/img]





I welded a plate between my twin cross tubes that had bosses welded underneath. These were tapped through, plate and boss,
and stepped swivel washers made to fit the seat belt ends. (see photo)

Paul G

Rescued attachment top-s-b-mounts-s.jpg
Rescued attachment top-s-b-mounts-s.jpg






Member of the Suttol Owners Club, the MX5 Owners Club and the BMMC

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40inches

posted on 5/5/19 at 06:56 PM Reply With Quote
Looked at the Westfield chassis at Stoneleigh today, the rear belt mounts are the same as MK, but without the
strengthening added, this is a type approved left hand drive chassis

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Stuart Walker

posted on 28/10/19 at 10:06 AM Reply With Quote
Finally done this weekend, and I did it properly in the end. Now to try to match the paint... Reckon I'll just repaint the roll bars, then probably the whole chassis...

0106b8c 2a7ba812708083ecd0a7704ea93df4b4ad1 by Stuart Walker, on Flickr

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Mr Whippy

posted on 30/10/19 at 07:03 AM Reply With Quote

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