Corse I rear suspension failure

[hollytree]

3 hours, engine and gearbox out

steve

[john]

I think Steve's input had ceased by the time the Corse moved on to Alfa specific engine cradles, although it seems the rear suspension on the Corse I was always a work in progress.

[Strat Fan]

The first I chassis was the Honda version, this was the Gary Midwinter rally car that later moved on to Bernie Roonie. This was a Litton product, The first Ferrari based I chassis was also manufactured by Litton for Hugh Carson which is the yellow chassis seen in the Italian Super Cars guide. Darkspeed's Honda I was also a Litton era chassis.
The Alfa based rear cradle was developed by Hugh Carson & his brother David in circa 1992/3 around the same time that Neil fitted the 3.0 12v into his S chassis. Steve by this time was long gone so in reality probably never saw any of the Litton I chassis cars make it onto the road let alone have time to witness any failures.
CAE ceased trading in 1999 so again very few of the cars they produced would have done enough miles to show the limitations of the design.
The Ferrari & Honda cradles were lower which in turn made the offending hanging bracket less remote and less susceptible to leverage issues. The Alfa cradle was a lot higher which made the wishbone bracket very long & susceptible to fatigue.
Steve (Hollytree's) chassis has had an additional tube fitted but it is still too remote relative to the bracket & the second error in this case is that the bracket is not carried through to the upper tube for additional strength, the quality of the welding must be brought into question in this case aswell as the limitations in the design.
David May ran a couple of simple bolt in braces which prevented the fatigue issue from raising its head. Bob has a similar brace across the rear of the top wishbone mounts which can only help, a simple triangulated bolt in brace to the forward mount would also be a huge benefit.

[NoCorseChris]

Thanks for the extra info chaps.

It is easy to see problems with the benefit of hindsight isn't it. It's not as if chassis cracks on kit cars are unheard of either. Some big names in the business have suffered from that over the years.

Absolutely it's fixable, just somewhat of a shock to discover on ones own car I imagine!

[john]

Exactly as I understood the situation.
As I found it the production of the later I chassis left much to be desired and was a stark contrast to S chassis production.
I say this because there was a full set of drawings for the S. Properly drawn with full material specs and every engineering detail. All were notated as drawn by SG.
There was also some continuity in production.
The Alfa I chassis drawings were never complete, sparse in detail and dimensions and most fabrication was done from detail contained in a red hardback notebook at the fabrication shop. This had been passed down from the S chassis fabricator.
Sporadic production cannot have helped either as lack of continuity meant that critical dimensions and details may well have been missed. Development would also suffer, naturally.
Couple all this with a complete disinterest at the fabrication shop who really did have better and profitable things to do, and no wonder that things went wrong.

[GrahamH]

Exactly as I understood the situation. As I found it the production of the later I chassis left much to be desired and was a stark contrast to S chassis production. I say this because there was a full set of drawings for the S. Properly drawn with full material specs and every engineering detail. All were notated as drawn by SG. There was also some continuity in production. The Alfa I chassis drawings were never complete, sparse in detail and dimensions and most fabrication was done from detail contained in a red hardback notebook at the fabrication shop. This had been passed down from the S chassis fabricator. Sporadic production cannot have helped either as lack of continuity meant that critical dimensions and details may well have been missed. Development would also suffer, naturally. Couple all this with a complete disinterest at the fabrication shop who really did have better and profitable things to do, and no wonder that things went wrong.

Bad design in my view , poor understanding of loads and load paths , pretty shocking . Lucky it's easily fixable and hopefully before anyone has a major off.

[john]

Indeed. One of Carroll Smiths mantras was "Never ever put a load into the middle of a tube". And that is pretty much what was done there.

[mariner]

Hi,

Finally got around to hopefully sorting this potential problem on my car.
Made a simple bolt in bracket which runs diagonally from the front wishbone bolt back to the rear chassis.
Fairly straightforward for me having previously modified the rear chassis there was already an attachment point I could use.
When the engine was last out I had replaced the long diagonal tube with two shorter ones to give more room for the exhaust and at the same time fitted a brace across the car between the rear wishbone bolts.

rgds Bob