AT 35 Coupling

Submitted: Wednesday, Nov 10, 2004 at 18:58
ThreadID: 121577 Views:4271 Replies:9 FollowUps:2
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2 weeks ago, after towing our Bushtracker to a bush camp site for a weeks break, I found that the horizontal high tensile pivot bolt in the AT35 coupling had broken. There were no outside signs of it being broken and it was only discovered by accident when I was able to rotate the nut that is welded on and the broken piece came out in my hand. The break did not look recent and I wonder how long I have been towing with it like this.

Needless to say, it could have fallen out whilst towing and caused the van to drop onto its safety chains, I’m not looking forward to having over 3 tonne of van being towed by its safety chains at 100KPH.

After a trip to a couple of local town’s I was able to purchase a replacement bolt at a farm machinery merchants, not being able to weld the nut in place I bruised the thread enough to stop the nut from vibrating off on the trip home. The bolt broke where the thread meets the shank, I have posted a picture in Paul & Barbs album. While the bolt itself is ½” diameter, the weakest point is at the minor diameter of the thread which is only just over 3/8”. I intend to fit a bolt that has the shank long enough to cover the total width of the coupling and the threaded part outside of the pivoting area.

There is no way of checking the pivot bolt on these couplings as the nut is welded on, but I will look at other methods of retaining the bolt when I repair mine. I am only advising owners with this type of coupling of the problem that I had with mine so that they are made aware of what happened.

I sent an email and pictures to the suppliers of this coupling several days ago but as yet have had no reply.

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Reply By: Deleted User - Wednesday, Nov 10, 2004 at 20:37

Wednesday, Nov 10, 2004 at 20:37
wow thats not at all funny,certainly the shank should extend to the extremity and the end play taken with a split washer and a lock nut would be the go.I would also use a bolt by a reputable manufacturer ,there is inferior steel on the market particularily out of India,i also think 12.5mm (1/2) is too small, have a look at the size of the bolts used to secure the rest of the towing system check the internal diameter of the pivot point. for wear.and complain bitterley to the manufacturer,that should NOT happen I just had a look at the bolts used on my h/reese system and they are 16mm at the thread so probably 19mm (3/4) shank which woud be ok,cant find my micrometer to tell exactly
AnswerID: 565309

Reply By: Taj Mah Tracker - Wednesday, Nov 10, 2004 at 20:54

Wednesday, Nov 10, 2004 at 20:54
How long has the coupling been in use?, have you been in heavy off road conditions? approx how many Km would you have towed the tracker since new?
It is concerning
AnswerID: 565310

Follow Up By: Noosa Fox - Wednesday, Nov 10, 2004 at 22:28

Wednesday, Nov 10, 2004 at 22:28
Paul and Barb travelled to the Kimberleys with us earlier this year and we towed the Bushtrackers on some very rough corrugated roads.

I would suggest that you let Steve Gibbs at BTi know also, as an earlier coupling that they were using 3 years ago, broke on our van, and as a result all of that type of coupling were recalled and they went to the new supplier and the AT35 couplings.
I have found Steve to be very interested in safety faults that are located in any of the components that they use to build the caravans.

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FollowupID: 844096

Reply By: Andy1 - Wednesday, Nov 10, 2004 at 23:18

Wednesday, Nov 10, 2004 at 23:18

I noticed at Copeton that the AT35s on the most recent vans had what looked like a 3/4 bolt rather than the 1/2 on your and our van. We intend to replace the HR WD on our unit with a Reese & a couple of weeks ago I spoke to Bob Buchanan at Vehicle Components, the AT35 Manufacturer, to ask if they supplied an AT35 for the Reese unit. As the answer was yes I did not persue the bolt size as we will be purchasing the "new" model AT35 before our next trip.

Given your experience there should be a recall notice on the "old" model AT35 although replacement of the whole unit may not be necessary if a HT bolt is fitted as per your concept. The phone number for Vehicle Components is (07) 3262 2622, as your post will not be read by all Owners of BTs, or indeed all van owners with AT35s fitted I believe it is critical you phone Bob Buchanan.


AnswerID: 565311

Reply By: Freewheelers - Thursday, Nov 11, 2004 at 00:47

Thursday, Nov 11, 2004 at 00:47
paul & barb & possible others
peter is right threads on bolts should never be in the shear plane ie the body of the bolt should go through the cheek plates on either side from your photograph the thread is chewed up quite a bit so this has been happening for a while think yourself lucky
the bolt should also be high tensile steel if your replacement is not then change it soon also welding of high strength bolts is a no no so nylock nuts or lock nut or locktite should be used
Stephen & Deborah

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AnswerID: 565312

Reply By: Noosa Fox - Thursday, Nov 11, 2004 at 03:19

Thursday, Nov 11, 2004 at 03:19
I have been in contact with Steve Gibbs at BTi and he is very keen to hear from you and do everything that he can to rectify the problem. He will deal with Vehicle Components for you and make sure everything is done right.

I urge you to contact Steve Gibbs ASAP and if anyone else has problems with their vans, he asks that you contact them first to see if they are able to assist.

From experience, I know that I have had a few minor problems and they have always bent over backwards to help us.

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AnswerID: 565313

Reply By: Whatsnew01 - Saturday, Nov 13, 2004 at 03:51

Saturday, Nov 13, 2004 at 03:51
Paul & Barb

Did you receive my reply I posted to you re the AT35 coupling? I didn't see it appear as did the other replies on that subject. Perhaps I am doing something wrong or not posting it where it should go. Anyway let me know if you received it please.


AnswerID: 565314

Reply By: Paul and Barb - Saturday, Nov 13, 2004 at 21:41

Saturday, Nov 13, 2004 at 21:41
Peter, Ian, Brian, Andy, Stephen & Deborah, Roy,

Sorry about the delay in following up on your posts, after posting the original comment I headed off to hospital for a double hernia operation and this is the first opportunity that I have had to reply.

We have had the van for 15 months, since new, and travelled approximately 35000 klm with it. As Brian said, on our trip to the west we travelled on some very badly corrugated roads.

I have been a toolmaker for over 33 years and am familiar with shear strengths of materials and also welding of different materials. When welding high tensile materials, if they are not cooled down slowly they can develop cracks in the weld zone. This has not been the problem with the coupling as the nut was only welded on to stop it from vibrating off and cracks, if any, would not have penetrated very far.

I have still had no response from Vehicle Components so will phone them on Monday, also will contact Steve Gibbs with all details.

When I have more information I will post details.

Paul & Barb.
AnswerID: 565315

Follow Up By: Paul and Barb - Tuesday, Nov 23, 2004 at 03:48

Tuesday, Nov 23, 2004 at 03:48
I had a phone call from Vehicle Components early on the Monday morning and have now received a new coupling with a 3/4" pivot bolt, it sure looks like it will do the job.


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FollowupID: 844097

Reply By: Whatsnew01 - Saturday, Nov 27, 2004 at 02:04

Saturday, Nov 27, 2004 at 02:04
Gday Paul,

Interesting that the replacement coupling has a 3/4 inch bolt. The bolt on my coupling would only be 1/2inch. I have always thought to myself that that bolt looked a little light on given that the horizontal connecting pin is about 3/4inch diameter. Almost an admission that the smaller diameter bolt is suspect. I must say that I now feel quite uneasy about towing the BT with the smaller diameter bolt coupling in light of the experience you had. Did vehicle components or BT provide any clue or explanation as to why the smaller diameter bolt may have failed?? I would suggest that if there is any doubt at all about the safety of that coupling with the smaller diameter bolt then a recall is in order. Does anyone else agree with me?

AnswerID: 565316

Reply By: Flipp'n Lorry - Thursday, Dec 02, 2004 at 06:14

Thursday, Dec 02, 2004 at 06:14
I likewise agree that on closer inspection, the 1/2" bolt looks like a potential weak link in the whole coupling set up. And because the nut is welded on, it is not possible to do a visual inspection for wear or general condition.

I would like to be kept informed if there are any further developmetns on this topic.

AnswerID: 565317

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