Seat Belt Extenders

[fieryfred]

Evening all. I have listed this under a new heading moving on from "first Chim first post"
If you read that post i said i made a set of seat belt extenders & bought a set of seat belt guides.
I got in touch with Paul from stainlessforclassics & he said he would make a batch of extenders if i sent him a template.
Some people pre-ordered the extenders, he sent me a set to photo. Due to the extra cost these will not be listed on fleabay. He has 6 extender sets left & a few guides. You get the stainless extenders, bolts, washers & nyloc nuts. Its up to you to polish, paint or leave as is.
If your seat belt mounts have not been out for many years, better get 2 x 7/16" UNF bolts.
You will need an imperial socket or a 16mm to remove the bolt. The extender sits over the existing bush & crush washer. Its a fine thread bolt & is going now where fast, so just nip it up & allow the bracket to swivel. No need for Gorrilla force or scaffold poles. No doubt some one will know the torque setting for nip it up. The new bolt & washers attaches to your seat belt attachment. Same comment applies just nip it up & allow to swivel. If you want it tight thats fine.
Nowt to do with me i am just the messanger & they cost £25 inc p & p. I think thats a good price. I was going to add see my first post for his e mail address but its pages back now. So if you want extenders or guides get in touch with Paul. [e-mail]
Regards
Fred.

[fieryfred]

I forgot to add click on photo to see other photos.
Heres one i prepared earlier.

[bobfather]

Did this mod a while ago. It's worth curving the extenders downward to remover the downward leverage force. See link below

https://www.pistonheads.com/gassing/topic.asp?t=16...

[fieryfred]

Thanks for the reply. The force as is, is 90deg to the bolt so nothing has changed.
The existing mounting is unchanged. Curving will try to force the bolt upwards so i am happy as is.
Adding a curve will push the bolt into the carpet unless the brackets are much longer. The existing seat belt attachment has a 14.5mm hole i see from your sketch that you have an 11mm hole for a 10mm bolt. I added a 14mm sleeve to take up the slack on my own brackets. The new brackets have a 14mm stainless nut & bolt. This means you can mount the bracket either end.
I will let others make up their mind if a curve is required.
My concern is that the seats are held in place through fibre glass by 4 x 10mm bolts & repair washers. The seats will give way long before the seat belt mount. My body will give way long before the bolt & bracket.
What surprises me is that after all these years of seat belts being trapped by the targa hood making them useless that no one has come up with an off the shelf solution. Being a new Chim owner that surprised me. The crash test dummy said my seat belt does not work, meaning she would be through the windscreen with hard braking. Hence the bracket. With the seat belt guides added normal braking resumed.
Whats needed is a bar & beers, some one with years on Pistonheads & a Chim & a Griff owner peering through the window, that would put the world to rights.
Brexit anyone.

[bobfather]

The tower top slopes upward to the front, the seatbelt pulls in a horizontal or downward direction, lengthening the bracket multiplies the leverage force. I'm a mechanical engineer, the force acting on the tower bolt changes in nature and magnitude, that can be minimised by reducing the amount of downward force acting on the lever. I'm sure it'll be okay but don't think everything is the same, it is far from the same. You are increasing the length of the lever, that's like saying you can undo a bolt using just a socket, you add the wrench to increase the leverage force

[phillpot]

Another way to the same end.........................

[fieryfred]

I am also an Engineer & i know they work.
Lots of cars have seat belt extenders as standard, all located in different places & some with height adjustment.
Along with millions of other cars they have the industry standard 7/16" bolt.
Those millions of cars have the seat belt anchors located on various pillars & posts creating a myriad of different configurations. resulting in a wide variety of stresses being placed on the bolt from all directions.
In the TVR the directional stress varies with the seat location & height of the driver.
So a short bodied short legged driver with the seat pushed forward produced different stresses to a long legged, long bodied driver with the seat pushed back.
If the anchor point was known to fail millions of cars will have been recalled. The common failure is the condition of the webbing & reel.

So lets do some crash testing. I will allow the standard car to have the targa up to prevent the seat belt hanging loose in your lap making it totally useless.
I will run targa down with the extenders because the seat belt will never be trapped.
So what are the differences.

1. Side Impact. None. Both will hurt. No side impact bars or airbags.
2. Front end. None. No crumple zone or air bags. If the impact car is low enough it will hit the chassis first, if not its the wheels, tyres & engine.
3. Rear end. None. No crumple zone or air bags. Its the wheels, tyres & fuel tank to stop progress.

So apart from selling the TVR & getting a car with modern crumple zones & air bags the choice was simple.
I had a loose seat belt caused by the targa trapping it, & yes it was checked before setting off. So if that has happened to you fit the extenders. Straight , bent it does not matter as long as the seat belt works.
If it has never happened to you, then you dont need extenders.
The anchor bolt is more than capable & as i said in my previous post the weak link is you & the seat.

I hope i have tried to simplify the reasons & i am more than happy with the extenders.
I have show an MOT tester who does cars, bikes & vans. His comment was he thought i was trying to catch him out & if i had not told him, he thought they where standard.
So Gentlemen thank you for your time & reading the above.
I will leave it to you to decide what you want to do.
Unlike an MP i will not promise your children sweets or to eat them if you agree or dont agree with me.
Regards
Fred.

[bobfather]

http://thumbsnap.com/RjIluPTTou are being terrible defensive, you say you're an engineer and yet you also said that the addition of an extended lever didn't change anything. If you're an engineer then you must know that's wrong.

You appear to be assuming the tower mount can be compared with mounts on mass produced cars. The tower mount is a weak fixing, there isn't any metal bracketting or connection to the chassis. It's just a nut bonded into an extra thick bed of grp. If you add leverage forces that TVR Engineering never intended then you can easily break the mounting nut from the grp. Your local mot station won't have a clue that the construction method is so weak., I doubt even TVR speciallists could be qualified to assertain the effects of adding leverage to this fixing. kk

I didn't add the bend to my bracket for fun, there is a significant reduction in the forces acting on the bonded nut if you eliminate the downward force acting on the lever. As an engineer you must know this

You can see that by bending the extender plate the bolts are aligned so that pulling the belt forwards does not add any downward force on the fixing. I did this because the fixing is vulnerable

Edited by bobfather on Saturday 9th September 20:23

[fieryfred]

I am not being defensive, you are. Its not a 3' extension but 2". We all know that a captive nut is bonded into fibreglass. I am retired but i bet you are fun to work with & always like your own way. So i ran an engineering company for 27 years & always listened to peoples comments & concerns. So why dont we let grown men draw their own conclusions & make their own decisions. I will be at Lotherton hall on the 17th if you would like to meet over a coffee.

[N7GTX]

fieryfred said:

I will be at Lotherton hall on the 17th if you would like to meet over a coffee.

Hi Fred, I'll see you there.

[bobfather]

[phillpot]

bobfather said:

It's just a nut bonded into an extra thick bed of grp.

Is that really all there is to it?


Never chopped up a Griff or Chim body but on the S Series that top mount is welded to a huge, curved piece of steel strip bonded into the wheelarch.

I reckon you could pick the whole car up by them!

[bobfather]

phillpot said:

Is that really all there is to it?


Never chopped up a Griff or Chim body but on the S Series that top mount is welded to a huge, curved piece of steel strip bonded into the wheelarch.

I reckon you could pick the whole car up by them!

Yes there is a metal plate but it is secured into a brittle material. Seat belt mountings are normally secured into ductile materials much more capable of withstanding violent twisting that would occur if the mount was ever challenged to a real high speed collision. It took a lot of research to find this information before I designed the brackets on mine. It is a very strong mounting but definitely designed with specific and discrete forces in mind, that was my concern when I altered the dynamic forces on mine and the reason I felt compelled to comment here, I very much doubt owners know how this mounting is constructed.

As I said above, I'm sure these brackets will be fine, they are short. I'm not trying to undermine the OP, just sharing the design process I went through so that people can see a different approach. I only suggested bending this bracket to remove the potential of the additional force.

[fieryfred]

I met a Griff owner who asked if the seat belt extenders would fit his car. He was not in his car so i could not look & i dont know a local Griff owner to have a look. Has any Griff owner fitted the extenders. I assume they will fit, but its better to ask. He is not on PistonHeads so is missing out on a load of banter & info.
Regards
Fred.

[combine04]

Apologies if this raises old battles... but having just bought some flat versions from eBay, was there an answer to the slightly curved or not?

[bobfather]

combine04 said:

Apologies if this raises old battles... but having just bought some flat versions from eBay, was there an answer to the slightly curved or not?

I would advise that you stick them in a vice and hammer a curve into them. This will eliminate the leverage force that the straight bracket applies to the grp socket. Those top mounts are only secured into thick grp which can shatter if leverage is applied to the bolt

[phillpot]

I wouldn't lose any sleep over it, should you be unfortunate enough for your TVR to be in a crash severe enough to rip that out of the fiberglass I suspect it will be the least of your worries

[bobfather]

phillpot said:

I wouldn't lose any sleep over it, should you be unfortunate enough for your TVR to be in a crash severe enough to rip that out of the fiberglass I suspect it will be the least of your worries

The fracturing could be a gradual process, small cracks developing and creating each time leverage is applied to the mount. Better not to risk it in my opinion, why risk damage when a simple bend would eliminate the leverage action

[fieryfred]

The answer to your question is at the bottom of this post.
For me this was a safety issue. It prevents the seat belt rubbing on the carpet & being trapped when the hood is down.
If i did not think it was required i would not have made & fitted one & neither would Bob.
Read the above threads & Bob thinks the mounting points are inadequate with the wrong steel.
I am unaware of any failure of this top mounting point & i am happy to drive the car.
Ingnoring his personel comments the question he poses is to curve or not to curve.
If you think using a seat belt will result in fracturing & small cracks thats for you.
My opinion is that it wont.

So the answer to your question is you deceide.
If you think trying to curve a piece of 60mm long metal will make any difference then do it.
If not leave as is.