Member Since: 26 Feb 2009
Location: lancashire
Posts: 108
Cracked Wishbone!
After fitting a full Polybush wishbone kit last year the creaking from the bushes has got steadily worse so i thought i would try and put something on them.
When i got the car over a pit i noticed a big crack on the nearside rear upper wishbone front bush!.
I'm now going to replace both rear upper wishbones but leave the the standard bushes in.
Will this be ok because then i will have standard bushes on the top and Polybush on the bottom?
Has anyone seen this happen before? Could it be the Polybushes that has caused this?
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5th Aug 2011 8:15 am
amazing
Member Since: 05 Mar 2011
Location: chengdu
Posts: 1542
stressed out
the photo isn't too clear but it looks like the middle of the fracture has suffered elongation and failure earlier due to the rust traces then the outer edges which have a clean sudden recent tensile break.
the force passed from strut to mount is the same regardless of bush material but the shock stress will increase with stiffer bushes.
I had a similar failure on an old fiesta shock mount which split in the same manner this was due to corrosion swelling the pressed in bush housing.
but the polybushes are not pressed in are they??
past upgrading of bushes to polytype have omitted the outer pressed ring and have just popped in with a bit of soap..
do the originals have this outer pressed ring as if you use a hacksaw to cut it to aid removal you may damage the wishbone integity?
as for mixing bushes This is common practice for racing cars to alter handling (calling all 911 owners) so it will have an effect (negative or positive I don't know)It is better to have and not need it then need and not have it.
5th Aug 2011 9:34 am
cj730
Member Since: 26 Feb 2009
Location: lancashire
Posts: 108
No the Polybushes didn't need pressing in just a gentle tap!
Removing the old bushes wasn't easy had to apply lots of heat and force so it could have weakened the metal doing this.Disco 3 TDV6 HSE Auto Bonatti Grey
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5th Aug 2011 10:11 am
cj730
Member Since: 26 Feb 2009
Location: lancashire
Posts: 108
One thing i should have asked first!
Is it safe to drive? I'm not the getting the new parts till tuesdayDisco 3 TDV6 HSE Auto Bonatti Grey
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5th Aug 2011 10:38 am
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Member Since: 06 Nov 2006
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it may well just wallow a little more than it should. If it snaps altogether, then it would be more unstable, but it would be 'OK' to drive sedently....Bodsys Brake Bible
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5th Aug 2011 10:44 am
cj730
Member Since: 26 Feb 2009
Location: lancashire
Posts: 108
Thanks
What about mixing the bushes any thoughts?Disco 3 TDV6 HSE Auto Bonatti Grey
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5th Aug 2011 11:02 am
camelrock
Member Since: 11 Oct 2008
Location: north yorkshire
Posts: 446
I used to read about people fitting polybush kits in the 1990's on Range Rover, Disco's etc a year or so later finding cracks on there chassis, due to the stresses being transmitted through the harder bushes.
That's why pollybush released future kits with different grades of bush.
5th Aug 2011 12:17 pm
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
based on the photo, i wouldnt drive it
if you have an accident as a result of a failure, and worse - you injure or kill someone, and you knew about the fault (cos youve posted it here), good bye to any insurance claim/settlement and hello to a potential prosecution.Duncan
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5th Aug 2011 12:31 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26770
I wouldn't drive it either.
5th Aug 2011 3:24 pm
amazing
Member Since: 05 Mar 2011
Location: chengdu
Posts: 1542
Austinetic powers
"heat and force to remove old"
me thinkith you have found the answer to the fracture
You have "normalised" the low carbon steel
Normalizing is the process of raising the temperature to over 60 º C (108 ºF), above line A3 or line ACM fully into the Austenite range. It is held at this temperature to fully convert the structure into Austenite, and then removed form the heat and cooled at room temperature under natural convection. This results in a grain structure of fine Pearlite with excess of Ferrite or Cementite. The resulting material is soft; the degree of softness depends on the actual ambient conditions of cooling.
do not drive!! the wishbone may suffer catastrophic failure as the working load is about 100% more due to one side being cracked and not transfering load, The resulting failure..well that would be very messy .I had a front trailing arm break on an old car (VW beetle "hangs head in shame") very sudden instant right turn.It is better to have and not need it then need and not have it.
This is why you should never use heat to take bits apart, you can do all sorts of damage to the strength of fastener (bolts) and by the look of it wishbones too.
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7th Aug 2011 6:22 pm
catweasel
Member Since: 05 May 2006
Location: Bundaleer
Posts: 4805
hard to tell from the pic but looks like it has fractured along the weld and initial fracture is much older than the cracks on the tube section holding the bush.bottom crack appears to go under the weld. could it have been cracked prior and the install of the new bush has sped up the ultimate failure of the joint ?
7th Aug 2011 11:32 pm
cj730
Member Since: 26 Feb 2009
Location: lancashire
Posts: 108
Just removed the wishbone and there was a crack on the upperside which is a lot older which i didn't see till removed the whole wishbone.
I think i've been quite lucky the bush fell off as soon as i removed the wishbone with no force at all!
Click image to enlarge
ttp://www.disco3.co.uk/gallery/albums/userpics/15820/SAM_0067.JPG[/img]Disco 3 TDV6 HSE Auto Bonatti Grey
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9th Aug 2011 9:42 am
amazing
Member Since: 05 Mar 2011
Location: chengdu
Posts: 1542
lucky duck
oooh that could have been expensive or fatalIt is better to have and not need it then need and not have it.
9th Aug 2011 9:55 am
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20836
cj730 wrote:
I think i've been quite lucky the bush fell off as soon as i removed the wishbone with no force at all!
No
Never seen that happen before
At least you noticed it when you did. That could have ended badly...My D3 Build Thread
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