Failed Bolt - Suspension Arm

pete54 said:

I noticed a nut sitting under my Grenadier this afternoon - closer inspection revealed it to be the nut and part of the bolt (sheared through) from the rear passenger side suspension arm bush. Luckily it dropped off at home rather than out on the road! Has anyone else had this happen? On a positive note, response from Ineos Recovery (AA) was very swift - didn’t have a bolt of the same size but had one big enough at least to get me to the dealership (luckily only a few miles away for me). Hopefully will be a very quick fix although a replacement may need to be flown in. Only done around 990 miles.View attachment 7840661View attachment 7840662View attachment 7840663

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DaBull said:

Wow, Perhaps someone at the factory over torqued it?
DaBull

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Trialmaster said:

Or crappy Chinese metal!

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DaBull said:

Wow, Perhaps someone at the factory over torqued it?
DaBull

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pete54 said:

I noticed a nut sitting under my Grenadier this afternoon - closer inspection revealed it to be the nut and part of the bolt (sheared through) from the rear passenger side suspension arm bush. <snip>

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Miki said:

Do you mean the radius arm ?
An (approx_ 1M long) arm from the underside of the rear axle going forward to the chassis.

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• A = tensile strength of bolt in 100 N/mm2, used values typically 4, 6, 8, 10, and 12
• B = ratio yield strength/tensile strength x 10, typically 6. 8, or 9

• 4.6 is above mentioned crappy Chinese, used in non-critical locations, not usually available in Europe
• 5.8 very rarely used
• 8.8 most common grade, pretty standard in Europe
• 10.9 high strength, most Allen head bolts, typically used in suspension components
• 12.9 extreme strength

Tinerfeño said:

Replace the bolt and perform suspension alignment ...

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Miki said:

It's interesting that it has an indent in the bolt and the offset washer with corresponging pin on the washer. I presume this is to stop it twisting/roating against the cleat, ie so that it stays solid whilst the bushing rotates around the bolt ?.
If that is the case then why is it 'dry' ?

There is some force against that bolt (shear) as it's there to stop the axle from moving out of alignment with the chassis (backwards or forwards).
The rotation (of the bolt in the bush or the bush around the bolt) will allow the axle to move vertically (all be it in a slight curve), which it needs to do as the springs compress and expand.
I would suggest there is a real issue there.
That nut twisted off.
As the rear axle tried to move, the cleat held the bolt head and nut still, and the bushing rotated the bolt until it sheared.
It's likely it's a 10.9 HT bolt and as the axle moved (up or down) it simply (and effectively) sheared/twisted the nut off.

If it's supposed to move inside the bushing, then surely it should be greased ?
After a while the plating will wear off and that part of the car will oxidise quite quickly allowing the bolt to sieze the inside of the bushing.
I don't fully understand why the bolt is captive (or perhaps I have missinterpreted the shape of the washers ?).

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stickshifter said:

It is quite likely that the problem is one of a flaw in the steel of the bolt, or an over-torqued bolt - as others have said.

@Miki - I'm not sure about this, but from what I recall - if the bushing is rubber, you install the bolts dry, but if the bushing is polyurethane, you install with grease. Someone correct this if it is not right. What material are the Grenadier bushings made from?

To the OP @pete54
(1) Are you running larger tires or stock size?
(2) Are you running a suspension lift, or stock height?
(3) Have you been cycling the suspension off-road?

If the answer to one or more of these questions is "yes" than I wonder if part of the problem is that the rear lower control arm is not adjustable. The stock bushings do not allow for much lateral articulation. If you are doing a lot of technical off-roading / rock crawling. you might want to replace those arms with aftermarket ones - should those become available. Aftermarket arms for this purpose should (1) be adjustable in length, (2) have joints that provide for lateral articulation as well as the standard vertical or up/down articulation. See for example, the adjustable control arms made by Metalcloak for the Jeep JK. The JK came with short control arms - like the Grenadier - and so Metalcloak (and other companies) developed adjustable control arms that could be lengthened to accommodate a lifted suspension and larger tires - which is why I asked about tire size, suspension height, and type of driving.

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Our top of the line mid-arm Game Changing Suspension System outperforms all others, featuring patented technology available nowhere else. Features Include: Duroflex™ Joints enhanced with Kevlar True Dual Rate™ Coils Durotrak™ equipped track bars Height adjustable bump stops Specifically tuned...

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If the answer to all three questions (above) is "no", then it is most likely a defective bolt, or one that was over-torqued.

@anand - you mention that this was a "known issue" - was the bolt known to be from a batch of bolts that were bad, or just not spec'd to the appropriate strength?

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stickshifter said:

@anand - you mention that this was a "known issue" - was the bolt known to be from a batch of bolts that were bad, or just not spec'd to the appropriate strength?

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Tinerfeño said:

Bolts are classified according to strength in stardard ISO 898/2. Marking is: A.B, where:

• A = tensile strength of bolt in 100 N/mm2, used values typically 4, 6, 8, 10, and 12
• B = ratio yield strength/tensile strength x 10, typically 6. 8, or 9

Not all combinatons are available:

• 4.6 is above mentioned crappy Chinese, used in non-critical locations, not usually available in Europe
• 5.8 very rarely used
• 8.8 most common grade, pretty standard in Europe
• 10.9 high strength, most Allen head bolts, typically used in suspension components
• 12.9 extreme strength

Marking can be found from bolt head. If a Chinese bolt is graded to 10.9 it needs to fulfil the standard. Overtorque will break any bolt. One must remember that increasing strength class makes material more brittle and fatigue strenght may not increase respectively.

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