Broken Bullbar Bolts

Submitted: Wednesday, Oct 13, 2021 at 18:53
ThreadID: 142711 Views:1484 Replies:9 FollowUps:20
Anyone had the bolts break on their bullbar and if so what do you think caused it?

I have a 2019 Troopy fitted with a popular Australian commercial steel bullbar (I don't like naming brands but it is not ARB).
It developed a squeak so I thought I'd check the bolts and found that the heads of 6 of the M10 8.8 tensile bolts had broken off.
I took the bullbar off and found the 6 broken bolts were not actually clamping metal to metal - there was a 2mm gap between bullbar and chassis when the bolts were done up tight so the bolts were straddling a gap rather than clamping the bullbar to the chassis rail.
The bolts were always torqued to spec - when I fitted it myself and probably sometime since.

My only interest is to fix it and prevent it happening again. I do my fair share of corrugations - the vehicle has done the Canning, the ABH and lots of dirt road trips in outback SA, Qld and NSW.

Anyway I bought new bolts from Hobson to replace all the Chinese bolts and made up steel shims to space out the gaps between the bullbar mounts and chassis rails, so the bolts are doing their job.

Anything else I should do?
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Reply By: Peter_n_Margaret - Wednesday, Oct 13, 2021 at 19:21

Wednesday, Oct 13, 2021 at 19:21
Some OKA owners have similar problems with their bumper bars.
I would use socket head set screws, grade 12, high tensile flat washers and Nyloc nuts.
Cheers,
Peter
OKA196 motorhome
AnswerID: 638277

Follow Up By: Phil G - Wednesday, Oct 13, 2021 at 20:27

Wednesday, Oct 13, 2021 at 20:27
Gday Peter,
Interesting the OKA owners have a similar problem.
The bullbar uses the existing captured nuts in the chassis, so chance of nylocs.
I used high tensile washers and lock washers.
Hadn't considered socket head bolts, not sure why that would help?
I did consider going to 10.9 or 12 but I didn't want the bolts to be more brittle
Need some more time out in the GVD to give it a workout! Our trip out there last month was cancelled so we did the Gawler Ranges instead, and the corrugations were not as bad - I suspect the bolts may have been broken for a while and the remaining 6 bolts had done a good job to keep the bar on.
1
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Follow Up By: Peter_n_Margaret - Wednesday, Oct 13, 2021 at 22:11

Wednesday, Oct 13, 2021 at 22:11
Hex heads are typically only available to grade 10, not 12. Grade 12 socket head set screws will have higher tensile (and shear) strength for the same diameter and can be tightened to a higher torque. They are simply stronger.
Cheers,
Peter
OKA196 motorhome
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Reply By: Allan B (Sunshine Coast) - Wednesday, Oct 13, 2021 at 19:58

Wednesday, Oct 13, 2021 at 19:58
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Hi Phil,
I would suspect that the gap between bullbar and chassis permitted dynamic forces to cause stress on the bolts. I do know that such gaps are not permitted in structural steelwork. Your shims and new bolts should fix the issue.
Cheers
Allan

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AnswerID: 638278

Follow Up By: Phil G - Wednesday, Oct 13, 2021 at 20:33

Wednesday, Oct 13, 2021 at 20:33
Thanks Allan,
Yeah, I think you are right - the heads got stressed by the movement and snapped off - some were broken at the head and some were broken where the thread entered the captured nuts - they all came out easy enough - but I was surprised how easy it was to drill the bolts - might have been grade 8.8 Chinesium.

When I was considering the towbar I noticed the Toyota bar was supplied with shims to make it a tight fit and the Hayman Reese that I fitted did not - might check the bolts on it tomorrow!!!!
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Reply By: RMD - Wednesday, Oct 13, 2021 at 20:01

Wednesday, Oct 13, 2021 at 20:01
G'day Phil.
Just curious as to how there is a gap there now, which you have shimmed, but wasn't it there at time of fitting? If the bolts are from that "special supplier", maybe the quality although 8.8 , may well be less tensile than expected. Given the twist of chassis and localized stress at bolt heads maybe they, one at a time decided to let go as each took the stress in turn. Pull on 1 spot weld and it lets go and then the next etc,
If the bolts had little or no radius at the shank to head, ie, very abrupt and square, then they will likely fail as they are flexed, even tensile ones.
AnswerID: 638279

Follow Up By: Phil G - Wednesday, Oct 13, 2021 at 20:39

Wednesday, Oct 13, 2021 at 20:39
I fitted the bullbar when the Troopy was new - just followed the instructions to the letter. No shims.
The gap made the fitting really easy!! Slid straight on.
Yeah my first though was the bolts were no good - the head said JL brand 8.8 tensile - so I looked them up and they are a chinese bolt supplier so thats when I though I'd use an Australian brand I trusted and bought Hobson. The bolts I had to drill out were very easy to drill!!!
On my last trip we did a bit of 4wding over soem rocky tracks and I rember hearing a bang but not knowing what it was - I guess might have been a bolt letting go.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Oct 13, 2021 at 22:23

Wednesday, Oct 13, 2021 at 22:23
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There was a gap at the time of fitting. Phil said... "there was a 2mm gap between bullbar and chassis when the bolts were done up tight"
Cheers
Allan

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Reply By: tonysmc - Wednesday, Oct 13, 2021 at 22:17

Wednesday, Oct 13, 2021 at 22:17
Phil, Not your issue but I'm sure will start a conversation and food for thought. Many years ago while preparing for a trip to Cape York, I put high tensile bolts on my roof rack thinking they would of course stronger and better. After a zillion corrugations I found that most of the bolts had broken on the way up. I replaced them with standard bolts as it was all I could get up there and would be checking them every time we stopped all the way back. I made it the rest of the way up to the cape and all the way back to Victoria without any more issues and the standards bolts stayed in place for many more years without any problems.
I am not an engineer however I have always wondered if the high tensile bolts were actually too hard, being almost brittle whereas the standard bolts had a little bit of give or flexibility? I am certainly not suggesting just use standard bolts however it would be worth investigating what Toyota use (as yours is a troopy) for their bull bars and possible get the bolts from them as they should be the correct tensile strength?
Tony
AnswerID: 638280

Follow Up By: Member - McLaren3030 - Thursday, Oct 14, 2021 at 08:37

Thursday, Oct 14, 2021 at 08:37
I’m with you Tony,

The Off Road suspension (well respected and recognised brand) on my Off Road caravan uses high tensile bolts to hold the shocks in place. These broke on its first trip after travelling on corrugations, even though they were torqued to the recommended tension. Shocks and bolts were replaced under warranty by manufacturer, but suffered the same fate on the next trip on corrugations. I have since replaced all these bolts with galvanised bolts. Have not had a problem since. I now carry spare bolts as well as a spare shock absorber.

Macca.
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Follow Up By: Phil G - Thursday, Oct 14, 2021 at 09:03

Thursday, Oct 14, 2021 at 09:03
Macca, my offroad caravan has I think the same suspension as yours and I solved the issue by changing out the M12 8.8 twin shock bolts to 1/2" Grade 10 bolts that are slightly bigger, higher tensile and a tighter fit through the shock eyes to reduce movement. They also have a longer thread on the Nyloc nuts. I guess there's more than one way to skin a cat!!
The suspension manufacturer says that the bolts need to be checked and retorqued to 90Nm every service which I doubt the caravan service depts ever did.
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Reply By: axle - Thursday, Oct 14, 2021 at 08:53

Thursday, Oct 14, 2021 at 08:53
G/Day Phil,

I cant see how M10 bolts are heavy enough whether there hi tensile or not'

The other thing how far did the thread proceed along the bolt. if all the way to under side of head ,then they wont last., they most likely will shear off. you need some straight shank.

M12 black UNF with lock nuts and shimmed up would be my choice. But this is only my take on it.

Cheers Axle.

AnswerID: 638281

Follow Up By: Phil G - Thursday, Oct 14, 2021 at 09:17

Thursday, Oct 14, 2021 at 09:17
Thanks for you input Axle. Yeah I also think M10 is a bit undersized for a steel bullbar but that was the thread size available on the captured nuts on the chassis from where the bumper was mounted. I thought about upsizing to M12 but only one bolt was accessible enough to get a chisel in to knock off the captured nut. The bar is held on by 10xM10 and there is also two long M12s dropping down vertically. So there's a lot of bolts.

The bolts were 25 and 30mm long, so threads all the way to the head. Two had broken off at the head and had to be extracted before I could remove the bar and the others were broken where they entered the captured nut, so might not have made a difference.

The bullbar was a very rigid design - it didn't have any of the wobbly mounts found with say some of ARBs bars.

Anyway, its shimmed now and has better quality bolts, will go find some more corrugations and test it out!!
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Oct 14, 2021 at 11:04

Thursday, Oct 14, 2021 at 11:04
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Do you need help finding some corrugations Phil? lol
Cheers
Allan

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Follow Up By: Phil G - Thursday, Oct 14, 2021 at 11:08

Thursday, Oct 14, 2021 at 11:08
South Australia has more corrugations per head of population than the rest of Australia combined :-)
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Oct 14, 2021 at 11:11

Thursday, Oct 14, 2021 at 11:11
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Yeah, SA had its 'ups & downs' from way back in colonial days! :-(
Cheers
Allan

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Follow Up By: Briste - Thursday, Oct 14, 2021 at 16:00

Thursday, Oct 14, 2021 at 16:00
I blame it on the absence of convicts.
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Follow Up By: Life Member - Duncan W (WA) - Thursday, Oct 14, 2021 at 19:52

Thursday, Oct 14, 2021 at 19:52
WA makes and exports corrugations to SA just so as to share the love. LOL
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Follow Up By: Phil G - Thursday, Oct 14, 2021 at 20:13

Thursday, Oct 14, 2021 at 20:13
Yeah, had to think about WA and your dirt roads - when they are good, they are very, very good but when they are bad they are horrid!!!
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Reply By: Frank P (NSW) - Thursday, Oct 14, 2021 at 09:13

Thursday, Oct 14, 2021 at 09:13
Coming in late here, but I think the issue was the spaces, as Allan identified. That issue jumped out at me when I first read your post. I think that given how long your old M10 bolts lasted with the gaps, then with shims installed, quality M10 bolts should suffice. Whether they should grade 8.8 or higher is beyond my pay grade, but I suspect quality 8.8 with no gaps in the fitment will be fine.
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Follow Up By: Phil G - Thursday, Oct 14, 2021 at 09:22

Thursday, Oct 14, 2021 at 09:22
Thanks Frank,
I was surprised at the gaps in total, each mount had 4mm of gap and bolts coming in from both sides. The gaps were never going to close when tightening the bolts because the bullbar was too rigid and the steel too thick.
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Reply By: Keir & Marg - Thursday, Oct 14, 2021 at 10:05

Thursday, Oct 14, 2021 at 10:05
Plenty of info on the interwebby about mild steel versus high tensile steel. Here's an extract. Note the last sentence.
"What is High Tensile Steel?

High tensile steel is a type of mild carbon steel which has a high yield strength and tensile strength. It contains different alloying elements in order to increase the tensile strength of the steel. These elements include chromium, nickel, molybdenum, silicon, manganese and vanadium.

Moreover, it has considerably high fatigue strength and toughness as well. However, it shows a reduced plastic ductility and brittle fracture compared to many forms of mild steel."
AnswerID: 638283

Follow Up By: Zippo - Thursday, Oct 14, 2021 at 12:27

Thursday, Oct 14, 2021 at 12:27
" it shows a reduced plastic ductility and brittle fracture compared to many forms of mild steel."

That's where I was going to suggest earlier that the problem may lie. If Phil still has the failed bolts ("machine screws"?) or at least the heads, brittle fracture has a tell-tale appearance.

[Bolts vs machine screws: when I went through engineering, machine screws were all thread, and bolts were not. Maybe the terminology has gone fuzzy or merged since then. I know calling them all bolts is easier though.]
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Follow Up By: Peter_n_Margaret - Thursday, Oct 14, 2021 at 13:45

Thursday, Oct 14, 2021 at 13:45
" it shows a reduced plastic ductility and brittle fracture compared to many forms of mild steel."
I am no specialist in this subject, but if a piece of metal is being flexed to the extent that its fatigue life becomes an issue, it is too weak for the job it is doing.
A bigger bolt or a higher tensile bolt (or both) will improve its life, in my view.
Cheers,
Peter
OKA196 motorhome
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Follow Up By: RMD - Thursday, Oct 14, 2021 at 14:57

Thursday, Oct 14, 2021 at 14:57
I agree with Zippo, the suitability of Set screws/machine screws against actual bolts is probably the issue. If, through chassis twisting repeatedly, the bolts, not really bolts, will break seeing Phil has said the thread went to near the heads, Certain to fail. As Zippo mentioned, the fine grained fatigue break face tells a story of the type of failure. Someone mentioned about shear forces, Unlikely to be ANY shear forces unless hitting things, ie, Roos. unless it was the last few bolts flogging in the holes. The bolts certainly didn't shear. I am surprised the captive nuts held on to allow the fixing bolts to break just outside the chassis. Indicates bend forces repeatedly causing cracks and failure. He is lucky it is a heavy chassis, as many earlier BT50's and Rangers developed loose bolts for some reason and the bolts which held on simply fatigued the chassis and broke bits out of the chassis.

A conrod bolt has shank all the way through both halves and is ONLY threaded in the last mm or so where NO flex, only tension happens. It not like that they do not survive. Some I fitted to large machinery engines were not tightened to a torque, but "Free and Tightened length difference was the way they achieved uniform tension/tightness, ie, degree of Yield.
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Follow Up By: Phil G - Thursday, Oct 14, 2021 at 16:24

Thursday, Oct 14, 2021 at 16:24
Just remembered I had two photos. And yes, shearing forces were not part of it as the intact bolts would have prevented any shearing. All broken bolts were coming from the sides. Intact bolts were pointing to the rear

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Reply By: Phil B (WA) - Friday, Oct 15, 2021 at 08:16

Friday, Oct 15, 2021 at 08:16
In there somewhere we should also consider over-tightening of the bolts through the use of a rattle gun during installation.
Discovered this on a Troopie some years back.



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AnswerID: 638289

Follow Up By: Phil G - Friday, Oct 15, 2021 at 09:20

Friday, Oct 15, 2021 at 09:20
Gday Phil,
yes for sure.
The manufacturers seem a bit more conscious of correct torquing of bolts these days. The instructions for the bullbar I fitted here had all the torque settings (44Nm for the M10 and 70Nm for the M12) prominent on the front page of the fitting instructions.
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Reply By: Phil G - Friday, Oct 15, 2021 at 09:23

Friday, Oct 15, 2021 at 09:23
Thanks everyone for your help and discussion.

I was talking to a mate yesterday who has owned many Troopys and usually fits his own stuff and said the ARB bars are supplied with shims to get a tight fit. So I think we should be all good now.

Anyway, will report back in a couple of years!
AnswerID: 638291

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