F40 LM Restoration

The photo on post 907 and my post 909 on page 46.

That unusual angle on the wishbone joint to the hub is working against the natural arc of the suspension. It just does not look correct. I made a further comment on post 917.

Worth investigating even if to just discount it.

 

I guess the other questions are:-

a) are the mounting points to the engine cradle for LM suspension as per the road car cradle or were they modified from standard by Mich, especially the angle where the top of the shock mounts to the frame.

b) If they were the same as the road car, do you know yours is still to road car spec or could it have been modified to accept the previous group C style set up prior to your refurb.

If it were mine I would be showing that photo on post 907 to an independant suspension specialist/designer for their input, that pic makes my teeth itch, it just does not look right.

Something has introduced a side loading to the shock that should simply not be there. Wider wheels or incorrect offset also has an effect on the compression angle of the suspension, this is showing up with the way in which your tyres scrubbed out unevenly as well, unless that was just down the the angle the shock was sitting post breakage. Suspension is called the black art for good reason, it only takes a slight change in degrees to make a massive effect, all goes over the top of my head when the boffins start explaining it.

 

The angle of the bracket fixed on the hub looks to be slightly different on the other LM car which also appears to use a different design of hub for the brake caliper mounting points, hard to tell as the camera angles are not the same. Also the collar on the wishbone in which the spherical bearing sits is not welded quite to 90 degrees, if you were to take that wishbone, and swap it over to the other other side then that slight difference in angle would allow more upwards movement under compression of the suspension at that mounting point.

I am just a lightly experienced layman musing at something that does not appear correct to me, I could be miles out in my assumption.

The way I see it as the suspension arcs upwards and the shock is compressed then at a certain point any further movement at that particular suspension point is lost and the hub is then pushing directly against the wishbone, something then has to give, either the wishbone begins to bend which would show up as indents in the wishbone from the hub trying to bury itself, or the mounting point on the hub deflects, as its a cast item that will cause a crack or breakage, or at the other end the shock is taking a sideways load and breaks at its weakest point.

It will be interesting to see what the actual cause turns out to be, the race LMs were running very hard for many many hours and I guess never experienced this issue?

 

Sounds like you have found your problem then lateral movement as a result which broke away the top of the plunger of the shock, nice easy fix. Guess it was an assembly error at Koni?

 

Not a chance, they will just replace the component at best, its the way of the world these days, deny all responsibility.

 

I asked the same question on a motorsport forum frequented by F1 based guys and generally they seem to think the suspension in the photo is on full droop (even though it looks level) hence the unusual mounting angle of the wishbone, and once loaded up it would be far more level, and not the probable cause of the shock failure.

They also said any lateral loads would be taken up by the top mounted spherical bearing on the shock, so your findings about the collets being the wrong way around seem to be pointing in the correct direction as the cause of the failure.

Apologies for the red herring, I assumed it was not at full droop as the wishbones look parallel to the ground, I need to remember what they say about assumption!

 

Heck in that photo the drive shaft angle has me wondering, especially as it is going to be worse when on the ground and under (torque, suspension squatting) load.

Surely the driveshaft should be close to straight?
Pete

 

I think that pic shows my error far better, if you look at the angle of the stub axle, once the shock is loaded up on the ground the stub axle will run in the same line as the driveshafts and the wishbone mount would also level up.

 

I have the same Penske suspension - you're going to love it.

 

Ohhh my mouth waters...

 

On second thought, that driveshaft must surely not be connected to the gearbox.

I wish we could see a photo with the car on the ground and suspension in its correct position ...
Pete

 

Beautiful.