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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin 5exi builds

Marlin 5exi builds Calling all you sexi builders....sorry 5exi builders, show us your progress.

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  #1  
Old 12th September 2009, 17:57
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Default Broken rear wishbone!

Hi,

I was driving tonight about 65mph on a staright road approaching a slight left hander so backed off the throttle as I started to enter the corner and the rear of the car very nearly went!!

Very very scary stuff at that speed! I pulled over and inspected the rear to find a broken rear wishbone in exactly the same place as Rich h's car.....





This is far too much of a coincidence and really makes me think about what could have happened if it had totally gone?? As you can see the crack is about 2/3 of the way through.

As it's a weekend I have not contacted marlin yet so will wait and see what they say as two going in the same place is very serious and I certainly would not entertain driving my car again on the same replacement wishbones

My car has only covered 1300 (road) miles and never seen a track!! wishbones should last the life of a car.

Thanking my lucky stars tonight!!!!

Craig
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  #2  
Old 12th September 2009, 18:59
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Exclamation

Looks like Marlin need to be having a recall.

Out of interest, do you know when your wishbones and Rich's that have failed were manufactured.

...I've done 6500 miles on mine now....and OK still....but only 1600 power!

Bad batch maybe? ...or I'm running the gauntlet!!

Rich
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  #3  
Old 12th September 2009, 19:07
MikeR MikeR is offline
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Hi craig,

Looks like you were very lucky it could have been very nasty indeed.

Keep us informed as to Marlins response - i'm glad now that my car is
on its way to Track Developments for their new rear suspension upgrade.

Mike
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  #4  
Old 12th September 2009, 20:35
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Lightbulb Important - Broken Wishbone - design changed??

Hi Craig,

Just looking again at your picture of the broken wishbone and comparing it to mine.

To me, it looks like the design has subtely changed.

If you look on the gallery pictures at my rear end mod pic #2, you see that the wishbone tube and weld is right at the end of the wishbone...i.e. the weld that holds the wishbone tubes together is right at the tip of the threaded insert in the wishbone.....therefore, very little leverage / flex point during power / brake application. This is an early wishbone....circa 2005.

If you look at your pics the wishbone leg tube is welded to the other wishbone leg at what looks like approx 10mm inboard of the end of the threaded insert...maybe this is the problem??, gives a lever point for the threaded insert / ball joint arm to flex about....

Any thoughts.

Bigrich
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  #5  
Old 13th September 2009, 19:46
DavidH DavidH is offline
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Umm looking at my MK2 rear suspension it also has about 8-10mm guess its how far the insert is welded though that will be a factor in how much of a lever there is.
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  #6  
Old 13th September 2009, 20:42
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Craig, I'm pleased to hear you weren't hurt.

I hope that this failure further alerts people to the potential danger of cracks in their wishbones. The cut through image I posted in Ric H's thread I hoped would be enough for people to seriously consider strengthening their cars, but I'm not aware of anyone doing anything to avoid further instances.

Hopefully your failure will prompt people to act with preventative measures, rather than wait for theirs to fail and cause an unpleasant crash, by which time it could be game over......
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Old 14th September 2009, 00:52
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Glad that your caught it in time and that you are ok.

Marlin havn't got a great track record with wishbones recently have they?

Time to beef them up me'thinks as its not doing their reputation any good.

John
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Old 14th September 2009, 08:44
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It looks more like a shear failure at the weld rather than in bending
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  #9  
Old 14th September 2009, 10:52
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Craig

Like the others glad you are OK, this becomes a worry I feel for all of us.

I picked up on a comment from Bigrich that the point of welding where the tubes triangulate is further back on his, this was the issue I had on my front wishbones, the ones that were replaced by Marlin. Like others I too feel Marlin need to take ownership of this issue, it will be intersting to see their responce.

I understand from a suspension specialist with things like the wishbones when they are made they should be heat treated after welding, I wonder if Marlin do this.
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Old 14th September 2009, 18:18
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Yes as bigrich has said I defo think that having the welded tude nearer the end would help but also as John d has pointed out maybe thicker walled material.

It's also interesting that both cars have been honda cars?? maybe the lesser power cars will go but will take longer.

The crack is not the actual weld but just behind the weld!

It's very hard to see the other side with my car in the garage but in the same place the powder coat has cracked but not the actual metal yet!

It looks like a matter of time
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  #11  
Old 14th September 2009, 18:19
Ric H Ric H is offline
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Have you stolen my picture Craig?! That could be a carbon copy failure couldn't it! Glad you got away with it same as I did; mine had managed about 2500 miles.

I realise I never fed back to the forum the conclusion of my wishbone tale. I got a new pair from Marlin, and I spotted that, as Rich points out they seem to have returned to an earlier design where the diagonal is welded right to the tip - here's a pic:



I was reassured by this as it clearly removes the high bending load area that is where our wishbones have failed - where the weld of the diagonal is coincident with the end of the threaded insert. The tube gauge hasn't increased though - I checked by weighing and old and new bone. You'll see that Marlin were nice enough not to weld toe control arm tabs onto the arms (for me to cut off again) since they know I'm controlling the toe separately.

With that I swapped them both and haven't had a problem since, touch wood. The car has never been better since after fitting the new 'bones I've finally been able to drive it with the suspension tweaks. Did 600 miles last weekend without incident - great fun.

I know John thinks I should reinforce them and that may be a wise idea but the design tweak alone I think should have made a big difference. I'm going to be keeping a good eye on them for any cracks too...
Richard
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  #12  
Old 14th September 2009, 18:31
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Rich,

That looks much better! I still think the walls should be thicker though which would eliminate all my fears!

I was always brought up to over engineer if in any doubt!

It's obviously flexing that has caused both failures.

Will wait and see what marlin say

Craig

ps Can you feel the differance in driving from the old wishbones? Does it feel tighter?
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  #13  
Old 14th September 2009, 18:38
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Craig, as a slight aside, I'd be willing to bet the fitment of the 888s sped things up nicely. I have to be an absolute savage to make mine slip, so the loads through the suspension must be very high!
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Old 14th September 2009, 18:53
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Quote:
Originally Posted by craig View Post
ps Can you feel the differance in driving from the old wishbones? Does it feel tighter?
Well, it feels a lot tighter than a cracked wishbone....

I came to the conclusion that mine had had a small crack for a little while adding flexibility an causing the rear to pull to one side on overrun. With all the mods and adjustments I wouldn't like to comment on what has made most difference - but it certainly feels a damn sight better than it did.
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Old 29th September 2009, 22:38
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Got a new top wishbone yet?
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  #16  
Old 30th September 2009, 16:56
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Quote:
Originally Posted by alackofspeed View Post
Got a new top wishbone yet?

Hi John,

I have only just taken them off as been on holiday so will send them off to marlin soon!
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