John Brett

John is a professional engineer with 50 years experience.

John has designed and built many cars, trucks, and vehicle assembly facilities.

John has worked on design of roads, bridges, cranes, transmission towers, and buildings, and operation, maintenance and upgrade of hydro and gas turbine power stations.

John was a LVV Certifier for 13 years. John has long been a whistle-blower, expressing the view that the LVV system is dangerously deficient. John’s authority was revoked in December 2012.

John rides a 1992 Yamaha FJ1200ABS, and is also a keen road and off road cyclist.

APOLOGY

“The LVVTA has brought it to my attention that statements I have made in relation to it and its employees may have been perceived as defamatory.

I sincerely regret that and apologise for any harm caused. I have taken down the statements identified by the LVVTA of concern to it.

I have strong views about the low volume vehicle certification process and intend in the future to direct my energies into the public inquiry now being held in relation to it.”

John Brett 7th October 2015

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Aftermarket seats – the seatbelt buckle problem

Mnay enthusiasts want to fit aftermarket seats to their cars.
A problem arises when the original seat has the seatbelt buckle mounted on the seat, so that the seatbelt load goes through the slide rails to the car.
The easiest option is to keep the original slides, and mount the new seat to them. This way the seatbelt anchorage is unchanged.

If this is not possible, and the aftermarket seat has its own base and slide rails, this is where the problem arises.
There needs to be TEST DATA to show that the aftermarket rails are strong enough for the seatbelt load- and THERE NEVER IS ANY TEST DATA

There are two ways around this:
1 Fit a new Seatbelt Anchorage to the vehicle tunnel. This is done using standard Seatbelt Anchorage doubler plates of at least 3000 sq mm area (such as 80 x 50, or 100 x 40).
2 Bracketing the seatbelt buckle to the seat anchorage, using a piece of 40mm x 3 mm flat bar, usually about 100 to 150mm long, drilled for the 7/16 seatbelt bolt at one end, and drilled to fit the seat mounting bolt (usually M10) at the other.

It is a requirement that the Seatbelt is mounted with a 7/16 or M12 bolt. There are good reasons for this, and the seatbelt hardware is all made for this size of bolt.

The seat mounting bolt is whatever the vehicle manufacturer deemed appropriate- a M10 grade 8.8 bolt can take a shear load of 48 Kn, which is more than meets the load requirement for a seat and the seatbelt buckle loading.

The Manufacturers underfloor mounting plate for the seat is designed to take this load- the picture below shows that the seatbelt load in a standard seat is transmitted just to this one bolt- proving that this is true.
So we can rely on the Original, Factory seat mounting point, and the Original seat mounting bolt to take the seatbelt loads, the load just gets there by the new bar we have added.
NOTE- Remember to put the seatbelt load bar between the seat and the tunnel or floor.

S14 Seat showing Force Diagram

The LVV Standard for seats is 185-00. The LVV Standard for Seatbelts and anchorages is 175-00

6 comments to Aftermarket seats – the seatbelt buckle problem

  • johnbrett

    THIS COMMENT CENSORED

  • Very much appreciate it, thanks

  • Connor

    Can you please make a more detailed article on mounting the seatbelt anchorage to the tunnel, the do’s and don’ts?
    Thanks, Connor.

    • johnbrett

      Hi- There is a standard method for seat-belt anchorages using 3mm doubler plates usually 50 x 80 mm front and back, with monel pop-rivets through. We recommend you have this done by a seat belt specialist because they will have the parts and gear. If you need to do it yourself, we would prefer to talk you through it. Hope this helps

  • Frosty

    Hello, I’ve got a 56 chevy big back window truck. The pillar is very thin 20 m&m at the smallest and widens out slightly toward the glass. I am told that LVVTAwont issue an exemption for lap belts by my engineer who also said he felt the pillar was too flimsy to adequately support a seat belt anchorage. What’s the point in an engineer looking at it and saying it’s no good but telling me I won’t get an exemption.

    • johnbrett

      Hi Belair. Your engineer would be right that the pillar is not strong enough- who is it? The LVVTA are making all the decisions these days, not the Certifier. I would ring them on 04 2384343 and ask them to solve your problem.
      BTW I am sure that in the past I have engineered seat-belt anchorages for one of these. I think I used a dropper from the Cant rail, or a window bar.
      Regards

      John

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