Rear Upper Wishbone Cracks

[Sbfdave]

Car went in for its 7 year service at 35000 miles last week and was found to have cracks in both rear upper wishbones along the bore in which the spherical joint should be a press fit. Consequently both wishbones were free to move along the spherical joints until they made contact with the retaining lugs on the hub carriers. 

The first picture is the left hand wishbone and the second is the right hand and clearly shows the the contact area with the hub carrier after the spherical joint has slipped due to the relaxation of the interference fit in the wishbone bore. It is also apparent in the first picture how far the joint has moved since this is the as removed from the car state, i.e. the joint has not been pressed out following wishbone removal.

I suspect these both failed on the same day (last LEGS breakfast run) and within a couple of hundred miles of each other but there was no noticeable effect on the handling. 

We have had the car since new and it has never been tracked, never been off-road and never even been kerbed, so the failure is not due to excessive or abnormal loading.

Has anybody else experienced this.

 

 

[agentdr8]

There's been a few posts on LT about cracks in wishbones, which then allows the joint to move around. I think the failures always seem to be right at/near that cast line. 

[snowrx]

Scary😬

[Whitey]

Not heard of this before, but certainly of concern. If you've had your car from new, then presumably it's never had replacement ball joints fitted - so this must have been a fault in the forged wishbone casting, or possibly poor assembly at the factory.  I did have to replace a lower front wishbone earlier this year but that was because the lower ball joint was worn and this is not a serviceable item on the front lower wishbone. I bought an as new wishbone with the ball joint and the 2 pivot bushes already fitted from the factory. I bought this from ES Motorsports and was considerably cheaper than the new Lotus price on DeRoure. For ref, my car is a 2010 NA with 35k miles also and I've had it for 9.5 years since 3k miles so I know no suspension parts had previously been replaced. Please keep us updated on this - I will certainly be looking at my upper rear wishbones very closely!

[Spanky3]

I had the OS back wheel off a few weeks back and didn't spot any cracks but then again I wasn't looking for any either.   One cracked side is unlucky, to crack both looks a worry.  I'll check mine.

[Sbfdave]

16 hours ago, Spanky3 said:

I had the OS back wheel off a few weeks back and didn't spot any cracks but then again I wasn't looking for any either.   One cracked side is unlucky, to crack both looks a worry.  I'll check mine.

It is very easy to check. You can do it by looking through the wheel since the outer end of the wishbone is visible above the brake disc, and the failure site is right on the nose of the spherical joint housing where the casting/moulding line is. It should also be obvious if the spherical joint has moved within the wishbone and I reckon this would occur within a few miles of the crack appearing.

 

[Spanky3]

1 hour ago, Sbfdave said:

It is very easy to check. You can do it by looking through the wheel since the outer end of the wishbone is visible above the brake disc, and the failure site is right on the nose of the spherical joint housing where the casting/moulding line is.

Thanks, good point. Just checked my 2013 S and thankfully all fine.

[JimH]

Just checked mine too - 2014 S with 38k miles - all fine....

[Jason Trevor]

This happened on my 2011 MY N/A Evora and it is known to Lotus but they won't do owt about it , my car did have 99k miles on when it went though.

[Bibs]

Looking at the part numbers this is now a D level part, originally it was a B so it appears that is may have gone through a couple of revisions. 

 

[Sbfdave]

I noticed that the part number was updated, and the changes did not seem to relate to the bushes or spherical joint.

For the record (or anybody peering at their wishbones) both my failed ones have casting dates of March '13, although the car was manufactured in May '14.

[Gnasher68]

My 2013 SR went to Oakmere for servicing last Friday and I was told about this on the OSR wishbone. I was advised it's not safe to drive the car until replaced so had to leave it with them whilst a new wishbone is sent over.

My car has never been tracked or mistreated in any way during my 5 year ownership. It's covered 23K miles and was last serviced around 21K when all was well.

I've asked what Lotus are doing about it as from this forum and Lotus Talk I know of at least five cars that have been affected but Oakmere tell me Lotus are not interested due to the age of the car.

[DBG]

Checked my 2010 and both look ok.  Might be something I’ll have to keep an eye on!

[Julian73]

I would suggest using a dye penetrant, not just an unaided visual inspection, about $75 for a diy kit.

https://www.pegasusautoracing.com/productdetails.asp?RecID=1207

[racefan]

Soon available just waiting for pre production batch . made of billet and adjustbale camber with shims at the top.

i think 2 months they will be ready for our customers.

[Reindeer]

Just to help build a picture.....

Checked my 2013 SR this morning...

No cracks thankfully!

[TdM]

Unfortunately, by now, you would need to definitively prove that it's a manufacturing fault to force them to do anything about it, which is going to be super hard on an older car and a stressed component. We'll all just have to keep an eye on them

[Gnasher68]

I've paid for the repair and moved on but I'm interested in knowing the cause so I can try to prevent a recurrence if possible. That's why I asked for Lotus involvement. I asked for the old component and once home a few light taps were all that was needed to remove the spherical joint. Photos below of the joint and inner surface of wishbone.

Any opinions on this? I believe galvanic corrosion is possible but I'm definately no expert.

[Whitey]

Not sure if that is a corrosion issue or stress fracture, but I'm sure someone will know - Gaz at Spitfire Engineering would be a good bet. Was the repair basically a replacement upper wishbone, and has it been updated can you tell from the original?  The Billet wishbone posted by Racefan looks like it will be a good upgrade.

[a7esk]

Have lotus reviewed this issue Casting failure to me .

Year of manufacturing and batch codes they have on file .

just asking .

Eddie 

[ramjet]

I'm no metallurgist, but as a mechanical fitter, since all the cracks are appearing on the casting line, there is some sort of inherent weakness in that area. This is odd as there is essentially no difference between that area and 90deg away when the casting is poured. Removed from casting too soon after pouring? Different heat dispersion due to larger area at mould joint?

The other thing that would have to be checked is the interference between the inner bore of the wishbone and the outer diameter of the bush. Are some made with more interference than others when they are machined? Unfortunately, very difficult to ascertain once it has already happened.

It doesn't appear to happen to all cars from a certain model year and kms travelled does not seem to play a part as well.

I wonder what has to occur with a vehicle to warrant a recall? There is obviously some % in a certain period of time. This shouldn't happen, but saying 'we are not interested because of the age' is disappointing.

A billet wishbone will certainly be a good way to go.

[Gnasher68]

I agree its a stress fracture. I was just wondering if the black mark around the centre is corrosion between the steel joint and aluminium wishbone that has altered the interference fit and caused the fracture. As I say, I'm no expert.

[Vulcan Grey]

I agree that the casting roughness is definitely causing a stress riser there. I think the actual mechanism may be stress corrosion cracking, definitely made worse by the interference fit and the galvanic dissimilarity of the steel bushing in there. It would be better if that rough casting line were sanded down, and the wishbone were thicker there, but may be due to the choice of alloy. High strength aluminum alloys like 2024 and 7075 may suffer more to stress corrosion cracking than other alloys such as 6061 or 7050.

 

The wishbones should be protected from corrosion. A clear coating would be best so a crack could be easily seen if it forms. You could always oil them...

[au-yt]

I agree with Travis’s assessment, nice thing about 2024 it’s weldable, 7075, is what Boeing 747 wing planks are made from, as strong as it is it suffers from intergranular corrosion.

5058 would be more suitable allow.

As this raked a concern with the 400 it “ appears to be the same, but it’s easily inspected

[shakham]

On 11/07/2021 at 03:44, racefan said:

Soon available just waiting for pre production batch . made of billet and adjustbale camber with shims at the top.

i think 2 months they will be ready for our customers.

Any update on this? 

My dealer during service today told me that I have a hairline on upper right side control arm, so just a matter of time.  I have a 13 with 25K miles on it.  So something I'll likely have to deal with soon-ish.