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Author: Subject: Fitting lap & diagonal inertia seatbelts
David Jenkins

posted on 18/5/21 at 03:04 PM Reply With Quote
Fitting lap & diagonal inertia seatbelts

I currently have 4-point harnesses on my car and, although they're superb for track use, they are a PITA if I go from winter to summer clothing, or I take passengers of differing sizes. Basically, they're a bit of an unnecessary faff for the sort of driving I do (bumbling around country roads in a lively but not stupid manner). Ordinary 3-point inertia belts would be more than sufficient.

Has anyone converted their car from a full harness to lap & diagonals, and how did you do it?

Note: I have a very solid roll-bar that would almost certainly hold the upper belt guide after modification.





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nick205

posted on 18/5/21 at 03:32 PM Reply With Quote
Not fitted or even really considered it myself. I fitted 4 point harnesses in my MK Indy. They held you tight, but I did have that worry of "submarining" out them in an accident. It made me consider 5 point harnesses, but the prospect of having to make quite a structural chassis modification to attach the 5th point put me off in the end.

I'd have thought 3 point inertia belts used in tin tops must have to undergo pretty rigorous standards testing, including the mounting points for them. I was a passenger in a van crash a couple of years ago where the van flipped. The 3 point inertia belt kept me in the seat to the point I was still there (upside down) when the van came to rest.

Have you seen the harness pads you can get to slide over the harness straps?

Might be a way of making what you've got less uncomfortable.

[Edited on 18/5/21 by nick205]

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voucht

posted on 18/5/21 at 06:06 PM Reply With Quote
Hi,

Yes I did the conversion on my Haynes, because the 4-points harnesses I fitted in the first place strangely were not OK for Swedish IVA.

First I bought non-inertia seat-belts from CBS just for taking the tests, and then I bought inertia ones, still from CBS, the ones that can work both vertically or horizontally. There is an adjustment knob to set-up the position you fit the inertia roller, you can see it on the pictures below. Regular sedan inertia seat belts are mounted vertically and won't work horizontally, so it is important to have that in mind.

I fount it easier to fit the roller on the inside mounting points rather than on the outside.

It does not look very good on the roll bar, but with a bit of trimming it is OK. It would have been nicer to hide the rollers, but fitting them on one of the lower mounting points would be in the way of the seat when you want to slide it forward/backward, there absolutely no room for it between the seat and the trans tunnel or the seat and the side panel.

With the harnesses :

2014-08 -23_15-52-17 by Voucht sans_nom, sur Flickr

2014-08 -23_15-51-28 by Voucht sans_nom, sur Flickr

With the seatbelts :

IMG_027 0 by Voucht sans_nom, sur Flickr

IMG_026 9 by Voucht sans_nom, sur Flickr

IMG_026 8 by Voucht sans_nom, sur Flickr

IMG_026 7 by Voucht sans_nom, sur Flickr

Hope that will help





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40inches

posted on 18/5/21 at 06:32 PM Reply With Quote
I did this about 5 years ago, wouldn't go back to a harness.
Photos near the bottom of this thread
https://www.locostbuilders.co.uk/forum/29/viewthread.php?tid=208273

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Mr Whippy

posted on 19/5/21 at 02:44 PM Reply With Quote
I did that too with my JBA Falcon after people kept complaining about the harness. Someone crashed into me and I smashed my face off the steering wheel and the windscreen due to the lap belts not reacting quick enough. Two black eyes, broken nose, gash across my chin and head, blood everywhere, plus 2 weeks concussion. Would have walked away without a scratch had I kept the harness. I'd also trust the harness to keep me hard back in the seat in a roll over where your head does tend to get close to the ground.
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JeffHs

posted on 20/5/21 at 03:47 PM Reply With Quote
I fitted 3 point from the outset. I used as new rear belts from a mk4/5 Escort. I fitted the inertia reels behind the seats in the space above and in front of the axle and made ali boxes to weatherproof. I cocked up the top mounts at first (too low) but once sorted no problems at all.
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David Jenkins

posted on 20/5/21 at 05:05 PM Reply With Quote
Voucht,

I like your method! Having the reels on the crossbar isn't ideal, but it looks like it would do the job. Are they OK mounted that way? Does the inertia mechanism work at that angle?

I will have to have a good think...





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