I too have a DO35 V1 coupling and I believe it has designs issues! While the V2 has recitified these issues, where does that leave us existing V1 customers ?
Below is a picture of a failed DO35 V1 coupling on a Quantum. I had email communication with Chris Goddard (MD of VC) on the 3/3/2011 after a previous post here on MySwag that showed the same pic below. At that time, VC were waiting for the coupling to be returned to the factory, but assured me that this was a rare failure. Well not long afterwards, another Quantum had a failed coupling when shunted from behind (pic 3). At this time, approx 200 Quantums have been made and now there have been 2 failures. Both these failures were the result of the "U" section opening up after considerabe force was applied.
1st Failed DO35 V1 (vehicle and Quantum hit rock on side of road with sufficent force to break rear 200 series rim, bend the axle and cause this coupling failure when van wheel hit rock - suspension arm of van replaced)
2nd failed DO35 V1 (coupling was similair to pic 1, but this pic shows cause of failure - no significant damage to this ~1 week old Quantum except a chassis twist of 6mm on the high tensile chassis so written off by Insurance company)
On the V1, the only thing retaining the block in the U is the inherent strength of the U. On the V2 version, not only does the U strength retain the block, but a threaded section in the pins within the U join to the block, thus overcoming the original issue.
A secondary issue is that the coupling can rotate 180 and thus be connected upside down. This results in a severe reduction in articulation and the typical result is a bent yoke bolt when the U contacts the tow hitch while cornering. While the coupling does have a sticker labled "TOP" on it, once rotated the sticker cannot be seen and there is no way other measure to prevent its incorrect hitching. Again, this has been overcome in V2.
There are several other improvements in V2, but there is a fine line between what are design improvements and what are design faults present in V1. The problems mentioned by the OP are not necessarily design issues that affect the strength/safety IMHO that could result in a hitch failure, but are areas of potential improvement, which have actually been addressed in V2.
I had several email discussions with Paul White (Sales Manager VC) and Chris Goddard around the 4/11/2012 regarding the upside down issue and ultimately their final response was a ~30% discount on a V2 plus the comment "...
In the meantime we are quite happy that the coupling exceeds all legal strength standards..." (I had sent the above photos in 2011 emails along with several more in 2012 emails).
Now I was in a quandary whether to post my comments, but ultimately they are 100% factual and simply present the facts from my perspective and in no way are meant to denigrate VC, simply a portrayal of events and it is up to the reader to make their own mind up, if indeed that is even required! Apart from my previous MySwag post back in March 2011, the communications between VC and myself have not been "in the public eye". However, their comment that they "...try and exceed the expectations of customers...", well this is another customer side of a story to balance the manufacturer response.
Yes, I believe the V1 coupling does meet all legal strength requirements as VC state, but given two DO35 V1's failed on two Quantums (out of ~200 made), is there sufficent reserve strength for unusual events
I am unaware of any other failures on other brands of vans as I do not have access to this information. I have a Quantum and have access to the Owners Forum where these issues were discussed and is why I am aware of these two hitch failures, plus the "upside down" issue I had with my DO35. Given 2 from 200 failed (1%) this is an extrodinary co-incidence for a hitch on a top end van rated at 2.2T with a 3.5T rated hitch!
I understand that the cost to recall/replace V1 hitches would be astronomical, especially since they meet legal requirements and there is no "need" to. However, the fact that the V2 hitch seems to address the issues previously communicated to VC in March 2011, it seems they have acknowledged and rectified the issues present. Now given there is a significantly improved version available based on issues with V1, is this simply progress or does it warrant a replacement? Is a ~30% discount fair (likely close to wholesale price) or should a bigger discount be given? (I had a 10 year old Dyson vacuum cleaner replaced at 75% discount due to design faults of original - perhaps a benchmark of good customer service?)
My concern, as stated back in March 2011 to VC, is "...I have a ~$80K investment hanging off the back of it and I need the confidence it can handle my setup travelling at ~80km/hr on corrugated gravel roads and easily survive a hidden pothole or washout..." I still have this question today.
But... I also really like the other design features of this hitch, have used other brands before and do not want to go to another brand of hitch as, apart from the stated issues, the hitch is well made and fantastic to use. The V2 model simply fixes the V1 issues and makes it arguably the best hitch on the market. Anyway, at least MySwag members have another customer point of view.
Cheers
Captain
(Mark Peacock)
Note - MODS, if this is felt to be unfair against VC, then delete this post.