DIY Si
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| posted on 19/9/09 at 12:31 PM |
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Wishbone failure
Afternoon all.
Just got back in from an hour long hoon round the local highways. These are the bumpy-ish back roads that my Indy has lived on for 3 and a half years
now. Just exiting a favourite sets of bends not far from home, I decided to back off to go past an old farmhouse as there is often traffic coming and
the road narrows. Cue two cars coming the other way. So I go to slow down a bit, only to have the car turn quite sharply to the right!  That
weren't meant to happen me thinks, but it's not wise to stop and have a look on that short bit of road, and only being about a mile from
home I decided to very slowly drive home. The steering wheel had to be held left hand down a bit to maintain a straight line, but I thought it was
something like the front right locking on. Get home, jump out and have a nose round the front right. All looks fine to start with, until I notice this
on the left hand side:
Now this looks a little bit wrong!!
Anyone know what may have caused this? I've ot got time to pull the wishbone(s) off yet, but should do during the week. I thought the ends were
meant to be bits of tube, and as such fairly immune to this sort of split? Or is it likely to be the HAZ that may have caused this over time?
Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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speedyxjs
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| posted on 19/9/09 at 12:36 PM |
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Staple balls
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| posted on 19/9/09 at 12:37 PM |
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I'd say that's broke about there-ish.
Seems to be a fairly common spot for the lowers to go.
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DIY Si
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| posted on 19/9/09 at 12:46 PM |
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quote:
Originally posted by Staple balls
Seems to be a fairly common spot for the lowers to go.
Really? Whilst I've not done a search for threads, I've not heard for any regular failures since the thin locost bones.
Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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graememk
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| posted on 19/9/09 at 01:18 PM |
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a tie wrap should fix that.....
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iank
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| posted on 19/9/09 at 01:23 PM |
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The tube must have been ERW and it's split down the weld.
Someone was talking about this whilst making there bones a few weeks back. IIRC Best practice is to have the ERW weld in the middle so it gets welded
in either side.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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nitram38
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| posted on 19/9/09 at 01:28 PM |
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It doesn't have to be ERW, it may just be the welding causing a small burn back in the tube. This in time has caused a fracture along the weld
edge.
This is why I favour Tig over Mig for wishbones as you can watch the weld. Mig is too fast to see good penetration and can only be tested by cutting
through a weld or xraying it.
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sebastiaan
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| posted on 19/9/09 at 02:50 PM |
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The commonly accepted reason for these failures (i guess there were two similar ones a while back; one on a MAC1 I think) is that the crush tubes are
too short, causing the polybushes to bind, which in turn stresses the outer tube on the wichbone. This then causes a stress fracture in the HAZ.
I think......
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britishtrident
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| posted on 19/9/09 at 03:00 PM |
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If you actually look at the image properly the failure has occurred in the heat affected zone (HAZ) on the pviot tube adjacent to welded to the main
wishbone.
Without looking at more closely I would give a combination s of 3 factors as a first theory
(1) The weld caused a notch undercut at the end of the ptivot tube.
(2) The steel in the HAZ was brittle
(3) The pivot bush was tight or completely seized.
Result classic fatigue failure.
[Edited on 19/9/09 by britishtrident]
 
Rescued attachment n.jpg
[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]
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Minicooper
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| posted on 19/9/09 at 03:01 PM |
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On the 4 link 5 link setups used on escorts and the like they double up in the bush area by adding an additional 3mm thick strip
I'm well impressed with the 3GE wishbones I recieved but there has been 3 failures in as many months with these type of bush ends, so I will
strengthen the lower wishbones at least
David
 
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britishtrident
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| posted on 19/9/09 at 03:11 PM |
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If you look at tintop wishbones and radius arms you will see that the bush tube is always much wider than the radius rod welded to it this avoids
the weld intersecting the end of the bush tube and avoids causing a potential notch and stress raisng failure point.
[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]
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garyo
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| posted on 19/9/09 at 05:53 PM |
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I'd like to see a closer photo, but the break already looks brown, as though the crack has been there for a while, and rusted, before finally
letting go.
Gary
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mookaloid
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| posted on 19/9/09 at 05:54 PM |
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Not sure about the failure from a welding point of view, but It does seem that the bush was probably seized.
I have often wondered about fitting grease nipples to the wish bones and giving them a shot of grease every so often.
Has anyone done this?
Cheers
Mark
"That thing you're thinking - it wont be that."
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designer
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| posted on 19/9/09 at 06:13 PM |
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Although the picture is not that clear, the bolt seems to be badly corroded.
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MikeRJ
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| posted on 20/9/09 at 12:18 PM |
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I think stainless crush tubes should always be used; it doesn't take much corrosion to really tighten up a polyurethane bush.
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PAUL FISHER
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| posted on 20/9/09 at 01:44 PM |
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^^^^MikeRJ has made a good point,this would be a good modification.
Looks to me from the picture,that the crush tube has so severely corroded,this has caused the polybush to expand and seize round the crush tube,this
has put stress on the wishbone and weld and this has lead to its subsequent failure.
But,on the subject of general maintainance,without wanting to sound patronising.
I think the key point to be made is,as with any vehicle,but particularly with a self home built vehicle,and a very high performance one at that,you
can't just leave it until something fails,which results in a breakdown,damage to your vehicle,or a accident,you must ensure you have a
preventative maintainance system in place.We are all aware of various problems and failures and common faults we have on our cars,not only crush tubes
and poly bushes,but other item's by no means exhaustive list,but includes,rear camber wishbone nuts coming loose,rubbing brake pipes and fuel
pipes,bike engine drive coupling nuts and drive shaft torx bolts coming loose,etc etc,so these must be built into our service schedule,I would say 99%
of us service our own kit cars,so we are responsible to ensure its done correctly.
I would suggest these wishbones and all other suspension components should be stripped down once a year,any corrosion that has built up removed,and
re-lubricated,then built back up and ensure it is still functioning as it designed,should be part of your preventative maintenance.
[Edited on 19/05/04 by PAUL FISHER]
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flak monkey
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| posted on 20/9/09 at 02:35 PM |
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As has already been said by a couple of people, it does look like a classic failure of a weld in the HAZ.
There was another not very long ago, same thing.
Whether this is due to the poly bush siezing, or some other factor is difficult to tell from the photos.
Incidently I have my front wishbones off at the moment for a repaint. Even though the crsh tubes are the correct length (~0.5-0.75mm longer than the
bush) there is still some evidence that the bushes have been contacting the brackets. All of the joints were free to move however.
It may be wise to apply a small amount of lubrication to the end faces of the bush (not the crush tube!) when the suspension is assembled. Then there
is less likely to be any binding issues should the bush contact the brackets.
Secondly, as mentioned, crush tubes should always be made of stainless steel to prevent corrosion building up inside the bush which could also cause
it to lock up.
David
Sera
http://www.motosera.com
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DIY Si
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| posted on 20/9/09 at 03:39 PM |
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Right, I've managed to get the front bones off today. All of them moved freely once the coil overs were removed. Although the crush tubes were a
bit corroded, the broken bone in particular, I didn't realise it could make such a huge difference. Where the tube has split, it looks like it
had been undercut slightly when welded, although the crack itself is quite fresh for nearly all of the tube's width. Looks like it's a new
set of bones and some stainless crush tubes just to be on the safe side.
[Edited on 20/9/09 by DIY Si]
Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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