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Tow bar installation


Maverik
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I'm just about to fit a tow bar plate to my 86 LR90, its a 2nd hand one so missing a few bolts.

Whats the standard steel grade of bolts for tow bar applications? can I use standard 8.8 grade bolts or do I need something a little more exotic like 10.9

Its the bolts that fix the diagonal tie bars to the chassis and the bolts that hold the plate to the rear crossmember.

Cheers

Mav

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Those are the tow ball bolts, and as such 240Nm is designed for an M16, do that to an M10 and you'll likely be removing it in two pieces :)

Yours will need M10/12, unsure of which, as I don't have a Defender ;)

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A while ago I asked this question at a certain well-known trailer/towbar fitting specialist in Bristol and their reply was that they’ve always used 8.8 bolts with no reports of ill effects.

If you look in BS EN ISO 898-1 (“Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and studs”), it lists the nominal tensile strength of 8.8 as 800 N/mm2 and 10.9 as 1000 N/mm2 (The first 8 in 8.8 and 10 in 10.9, in fact). That’s 116000 PSI, for those who prefer to work in old money, or an absolute sh*tload in rough figures…

A more useful figure when doing bolt calculations, 0.2% of elongation, lists 640 and 900 N/mm2 respectively.

Bolts will have been sized to a huge factor of safety anyway, so I wouldn’t worry about fitting 8.8s. Just make sure you do the bolts up to the correct torque. Most DIY-priced torque wrenches only go up 200 Nm.

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