Broken inner shafts

[Jay]

This took me by surprise, especially the thickness of the shaft, although it was a nice clean conical break.
Might post the whole transaxle refurb, it’s been a hell of a journey. 

[chriswgawne]

That's slightly surprising to see the output shaft broken. On an Aurelia they are smaller and can be a weak point although Flaminia shafts/bearings can be substituted in the existing Aurelia casing without mod'n.
Chris

[dannels]

Wow - that explains your issue!

Guess you will have to stop doing those burn outs Julian!!!

[neil-yaj396]

The same thing happened years ago on a half shaft on my Frogeye Sprite. An engineer friend of mine attributed it to what he called a 'milling scratch'. A tiny fault in the casting that is exacerbated by the machining and allows fatigue to build up over the years until the part fails I think?

[Jay]

Having spoken to a few people in the know, this seems to be quite a common problem, Jaan at Eddins Moto mentioned that he has replaced 4 of them in recent years.

Maybe all the years of motoring have started to take their toll, with this being a weak link in the design. Strange as they look quite beefy.   

[Jay]

I see Classic Lancia replacement shafts look stronger
http://www.classiclancia.com/car-parts/index.php?route=product/product&keyword=flaminia&category_id=0&description=on&product_id=61

[chriswgawne]

Not sure that they do look stronger. I don't like seeing 90 degree angles on highly stressed parts. I have had several Aurelia propshafts fail whilst racing....and always where there is a 90 degree step. Lancia engineering design was always pretty good IMHO.
Chris

[Jay]

My thoughts are that the Classic’s shafts have a greater diameter as it is the same as the outer diameter of the inner spline. Whereas Lancia look like they are turned down narrower to the inner diameter, so overall diameter is less.

I guess this is also to do with ease of production with only straight turning, the stepped middle section is for the outer seal.

[JohnMillham]

Not sure that they do look stronger. I don't like seeing 90 degree angles on highly stressed parts. I have had several Aurelia propshafts fail whilst racing....and always where there is a 90 degree step. Lancia engineering design was always pretty good IMHO.
Chris

not unlike crankshafts, where Lancias always made them with a nice radius at the corners, but subsequent regrinds don't always!
Regards, John