12 replies to this topic

[PAUL S]

I know there are some boffins in the black art here in this subforum, so would love to hear your expert opinion on this matter.

The owner of the car below has had a suspension failure, the top of the shock plunger broke away from its mounting, I had previously mentioned that the area in the red circle did not look right, and after the shock broke I suggested the awkward angle in which the wishbone is mounted to the hub could be causing lateral movement in the shock causing the failure. He is adamant it has been set up as per the factory cars and is correct.

I am by no means an expert and typically work on the basis is it looks right then it is, if it does not then why?

I would like to hear the opinion of those well versed in suspension as to why the area in the red circle sits at such an awkward angle.

 

[PAUL S]

Thanks, my assumption was it is not at full droop as the wishbones seem parallel to the ground and the disc looks to be at 90 degrees to the ground so the suspension is sitting as it would when a wheel is fixed and the car is on the ground holding its own weight

 

But then again what is it they say about assumption! 

[kikiturbo2]

normally the shock would be mounted with spherical bearings at each end, so some lateral movement wouldnt pose a problem.. That mounting angle of the bearing in question is not all that weird and will be a "worst case scenario" at full drop. In any case, it will be a potential failure point itself and not a casue of the damper failure..

[gruntguru]

The circled joint should only look like that at full droop. Any additional droop travel will cause the joint to bind.

 

Not related to damper mount failure though, in any way that I can see.

[Newfoundlander]

It is the R/F A-arm installed upside down on the L/F suspension would be my guess.

[Bloggsworth]

All the spherical bearings look to be mounted at 90 degrees to what you would expect...

[fredeuce]

All the spherical bearings look to be mounted at 90 degrees to what you would expect...

 

I have to agree with this . I would have thought the axis for these spherical bearings would need to be in a longitudinal manner , that is in line with front and rear of the vehicle.

 

I would like to know more about the vehicle and what it is used for and a picture of the area where the failure occurred. Given that the shock strut in fact carries the weight of the vehicle an event like bottoming out could result in a failure of the top mount. I would like to know what the driver was doing when the failure occurred.

 

More information and photos are needed.

Edited by fredeuce, 22 July 2015 - 05:37.

[Greg Locock]

I agree with Bloggsworthy. bolt axes are just wrong.

[gruntguru]

It is not unusual for rod-ends to be oriented with the bolt axis at 90 deg to the joint rotation axis. The designer just needs to be sure the joint rotation is within limits imposed by the rod-end geometry.

[Greg Locock]

Yes, but there doesn't seem any attempt to preserve what articulation there is, the sleeves look perilously close to binding on the inboard ends of the A arms, as well as the circled one.

[saudoso]

Looks like a 7 errors game

[kikiturbo2]

All the spherical bearings look to be mounted at 90 degrees to what you would expect...

for a road car yes, for a track car quite an usual design... ok, we dont know if the designer did his job and ensured there is enough travel for the joints not to bind..

[PAUL S]

Its actually an original F40 road car that was converted in period to a race car, it has recently been restored but to full LM specification using all the correct parts as supplied by Michelloto who built the original LM spec cars for Ferrari, the suspension you see is all brand new.

 

It now appears that the tapered collets to the top mounts that hold the bearing on the top of the shocks was fitted upside down, along lateral movement of the shock plunger, causing it to fail the first time the car was tested in anger recently at Anglesey. The pic I have been told does show the suspension at full droop even though the wishbones look parallel to the ground, hence the unusual angle where the top wishbone mounts to the hub, once under load it is much straighter.

 

Thanks to all that contributed.