Oooh-Er Look At This!

[Longboarder]

A modified pic of Shafts bracing bars.

Twice today I have sat down to post on this thread and been distracted. IMO the issue is one of unopposed torsional stress being fed into a chassis member. The lower rear wishbone mount has the bush some 4-5cm below the centre of the chassis member. Acceleration/deceleration/impact stresses are fed horizontally into the mount by the wishbone rear member. The mount acts as a lever imparting torsional stress into the chassis member twisting it to and fro and has led to a stress fracture at the weak point in that member, the weld affected zone. The bracing bar dissipates that torsional stress into a compressive stress in the bracing bar and possibly a minimal bending stress in the rear cross member.

 

This has the potential to be a failure point for all zeros that do not have the bracing bars added to later chassis. GBS will no doubt be contacting all zero owners about this safety issue! I don't know if they can identify from records all chassis that don't have the brace. It may be that each zero owner will have to be alerted and have a look under their car to see if they need it. I'm sure GBS will do the job for any owner who can get their car to GBS. For more distant owners perhaps they will issue a kit of bits, instructions and pics/diagrams/dimensions/specifications so they can get it done by a local competent welder. Costs would be an issue for later. Safety first.

 

Nigel

[richardm6994]

Ollie, you've had a lucky escape! Things could have been a whole lot worse!

 

I've not built a zero so I'm not familiar with it's chassis, however from the photos uploaded on this thread I think that the lads are spot on with their diagnostic as to why the failure has happened (i.e. not having the additional brackets).

 

GBSC have also identified this potential failure point within their design as later chassis have been provided with the addition brackets, albeit I'm sure GBSC thought the risk of failure was very low and that the additional brackets was just a precaution?

 

Now that this potential failure has been proven in the "real world" (thankfully without any serious consequences), I hope that GBSC are able to trace all of these original chassis's and correct the problem (or at very least tell the owner of the problem). In reality though, many zeros have been sold part built / fully build so tracing the new owners would be very difficult (especially the part build zeros).

 

I remember reading on the "name change" thread that the majority of RHOCAR members do not use this forum therefore I'm sure that a number of them will be Zero owners & unaware of this problem! Would it be worth mentioning something in the club magazine? I'm not into scare mongering but as a club surely we should do what we can to make member aware of this potentially disastrous problem? (I remeber a big deal being made out of the failure point on the exmo front suspention buttress)

[knights_templar]

Hi Longboarder

 

very plausible, but IMO that would have shown twisting between the front and rear brackets, as any force on one mount would be equal and opposite to that on the other. Shafts theory of tight bushes would transmit a twisting force onto the chassis, with a higher frequency and bending moment, and not effect the connection between the mounts.

 

speculation at this point, to which you could add other factors such as faulty material, poor build, by both manufacturer and or builder, or external forces such as a previous accident, as well as design, are just that, speculation

 

dramatic and disconcerting as the pictures are, Ollie does say he had returned home after a run out, so the chassis must have been in one piece, probably weakened, producing unusual handling or noises that prompted investigation, but not as we see it now.

 

how much of the resultant evidence is therefore failure and how much is investigation can not be assessed without inspection by experts.

 

you only have to go here

 

http://www.vosa.gov.uk/vosa/apps/recalls/default.asp

 

to see that manufactures can get it wrong, and that’s only those that are current.

 

GBS appear to have agreed to look at the problem. at this stage all we can do is wait for the facts, and any appropriate action deemed necessary after assessment.

[Guest zoomzoom]

My Zero was bought in 2007 so is one of the first. Just been looking through my build pictures and my cars rear end is different to that of Ollie's and Shaft's it has a tube running from the inside of the lower rear wishbone mount to the bottom of the fuel tank tube and the same on the other side which meet in a 'v'. hope you can see from this picture.

 

 

not the best view but i will be checking my car to night and see if i have a better pic to put up

 

Marcus

[Guest mower man]

My Zero was bought in 2007 so is one of the first. Just been looking through my build pictures and my cars rear end is different to that of Ollie's and Shaft's it has a tube running from the inside of the lower rear wishbone mount to the bottom of the fuel tank tube and the same on the other side which meet in a 'v'. hope you can see from this picture.

 

 

not the best view but i will be checking my car to night and see if i have a better pic to put up

 

Marcus

That photo shows a bracing member which would have stopped the detachment as shown in earlier images. Do I not remember an ask about knocking sounds from rear suspion in some earlier threads ,I may be off track I'm not sure mower man

[agent_zed]

Might be putting the cat amongst the pigeons but i can't believe that the bush sleeving being too long would cause such a catastrophic failure. Whilst i agree if the holes weren't aligned you would get, as you say, additional force on the brackets as the suspension moved and bound at certain points. but the sleeves simply being too long by a couple of mm too long would surely only pinch the bracket up tight or stretch it out a bit. If the tolerances are that fine that by being 1 or 2mm out the chassis will snap then we should not be making these in our garages.

 

I would have expected the suspension mount to rip off first before the crossmember, as the mount would be under stress?! but i guess by what has happened it couldn't have been the weakest link.

 

be interesting to know the cause, when you get it back from gbs.

 

just my thoughts on it (definitely far from an expert)

[Grim]

Agent Zed: it does happen, see the wishbone failure here: http://www.locostbuilders.co.uk/viewthread.php?tid=139225

In this case the chassis has failed, the bracing on other cars would help, but i think the crush tube is the fundamental issue here.

[agent_zed]

Hi Grim,

 

but isn't that failure more to do with either - a weak wishbone tube (seam welded), incorrectly aligned holes (leading to extra stress) or seized bush (leading to extra stress). Too short and i agree it would put extra pressure on the bushes, which seems to be what they are saying in that thread as it pinches up on the bush. I can't see why a slightly longer crush tube would cause that failure.

 

i am probably missing something but providing the holes are inline between the wishbone bushes and it moves up and down freely, why would the crush tube being slightly too long put any more pressure on the pivot? The only thing i can see it doing is pushing out the mountings slightly and allowing a bit of slop back and forth (obv not brilliant to have)

 

I really don't mean this to come across as an argument as i don't know, just interested in the theory behind it.

 

If the crush tubes/alignment are that critical i am surprised we don't see more problems in the 2b as we had to drill the 2nd holes in the top suspension mount, trying to get the holes all lined up correctly! eeek maybe i'll give it a check later.

 

cheers

[Guest ollie chapman]

Hi, just thought I'd come in here again on the bushes point - there was plenty of smooth play in the bushes - not too tight nor any great side to side movement - when the bottom of the wishbone was still attached to the piece that came off. GBS have said they will do a complete upgrade of the rear end to bring it in line with current Zero chassis and a thorough inspection of the rest with remedial work if necessary. They say it is a pre-production chassis but are still running a car on the same design with no issues despite having had a fair degree of use. I have confidence in GBS and I am sure everything will turn out right.

[Shaft]

Hi Grim,

 

but isn't that failure more to do with either - a weak wishbone tube (seam welded), incorrectly aligned holes (leading to extra stress) or seized bush (leading to extra stress). Too short and i agree it would put extra pressure on the bushes, which seems to be what they are saying in that thread as it pinches up on the bush. I can't see why a slightly longer crush tube would cause that failure.

 

i am probably missing something but providing the holes are inline between the wishbone bushes and it moves up and down freely, why would the crush tube being slightly too long put any more pressure on the pivot? The only thing i can see it doing is pushing out the mountings slightly and allowing a bit of slop back and forth (obv not brilliant to have)

 

I really don't mean this to come across as an argument as i don't know, just interested in the theory behind it.

 

If the crush tubes/alignment are that critical i am surprised we don't see more problems in the 2b as we had to drill the 2nd holes in the top suspension mount, trying to get the holes all lined up correctly! eeek maybe i'll give it a check later.

 

cheers

 

 

It's if the crush tubes are too short that makes it a problem, not if they're too long.

Short tubes (i.e. no protrusion past the bushes) would make them useless and allow the

chassis to clamp up solid against the wishbones.

[Grim]

Thanks Nick for fielding that.

 

I must say well done to GBS for their response.

[Shaft]

I agree Andy, sorting the problem without quibble on a vehicle thats been on the road a while

is a fantastic response in my book.

 

Hopefully it'll be an isolated problem for both the Zero owners and GBS.

Checked mine this afternoon and it's solid, no signs of stress or crazing/cracking

in the powder coat.

[knights_templar]

My Zero was bought in 2007 so is one of the first. Just been looking through my build pictures and my cars rear end is different to that of Ollie's and Shaft's it has a tube running from the inside of the lower rear wishbone mount to the bottom of the fuel tank tube and the same on the other side which meet in a 'v'. hope you can see from this picture.

 

 

not the best view but i will be checking my car to night and see if i have a better pic to put up

 

Marcus

 

so a 2007 chassis has the bracing, as does shafts 2009, but one circa 2008 does not?

 

Hi, just thought I'd come in here again on the bushes point - there was plenty of smooth play in the bushes - not too tight nor any great side to side movement - when the bottom of the wishbone was still attached to the piece that came off. GBS have said they will do a complete upgrade of the rear end to bring it in line with current Zero chassis and a thorough inspection of the rest with remedial work if necessary. They say it is a pre-production chassis but are still running a car on the same design with no issues despite having had a fair degree of use. I have confidence in GBS and I am sure everything will turn out right.

 

this may be the answer, a pre-production R&D chassis. so that would put it prior to Marcus's version.

 

Ollie did you purchase it from GBS directly?

 

I know they have sold off R&D vehicles in the past, I can think of two three wheelers and a four wheel drive thing, but as that, for further R&D, no guarantees.

 

so pleasantly surprised they have agreed to the above.

[Longboarder]

Every zero owner should check their chassis to make sure they have the two bracing members in place. If they are there then you have no problem. Zoomzoom's chassis bought 2007 has them. Do all production chassis have this bracing? Ollie appears to have a development/pre-production chassis which although he bought it in 2008, it's not had the production mods applied to it. How was that released for sale? Are there any others that have been sold which have this potential problem?

GBS need to get proactive in recalling or correcting any other chassis that have this fault. It would be most interesting to know how the modification came about. Did computer modelling of stress effects highlight the potential failure and lead to the modification or did GBS have a failure in a development chassis? The fact that an early similar chassis without the bracing is still in use without failure is not reassuring. It's continued use when a safety mod had been recognised as necessary (and now proven by this failure) suggests GBS had not given appropriate importance to the safety aspect this mod addresses. I hope they will not use it further before applying the bracing.

GBS are sorting Ollies individual problem without delay but that's only one of the issues needing urgent attention here.

 

Nigel

 

I think zoomzoom and shafts chassis have identical bracing.

[Guest scrabster]

evening all,just checked my chassis pics which was bought in april 2008, happy to say it has the diagonal braceing fitted.

regards,jess.