Tarmac Rally Stratos Build begins

[Strat Fan]

So this was the sort of failure we were attempting to avoid with the additional strap


Now 'm not saying this is absolutely correct, but here was our thinking on the situation


- the failed section is after the gearbox mount, so it won't be subject to any loads generated between the diff output to the chassis


- the only Force that part of the gearbox casting is subject to is created from the gear shaft bearings


- As the gears are loaded up the shafts will try and spread apart, this is reacted by the bearing housings in the casting


So our thoughts were, a failure occurred in the casting between the 2 bearings, as mentioned it is very very thin in there, once a crack formed the 2 gears spread apart further and caused the carnage seen in that photo


What would be super helpful would be a photo of the failed casting parts, if the 2 bearing housing are still attached together in the end plate that would falsify our theory

I haven't got any other pics of the failure so can't comment on what the other piece looked like.
You can try DM'ing the owner, Sando on here but he sold his car a couple of years back and hasn't checked into the forum since Nov 2020.
You may be right on the failure being caused by the shafts trying to separate, I was thinking it was related to the thrust on the shafts induced by the helical cut of the gears/crown wheel.

[Stableblock]

There will also be an axial thrust from the taper roller bearings tending to push the end off the casing. Your mod will help that by reducing the bending of the casing but ultimately the same forces have to be accommodated somewhere. As you say Colin more pics of the failure would help identify the cause.

[ProtoTipo]

Here's a 3.2 GT box

[Stableblock]

Thanks Chris, thats interesting. I note the extra ribs on the RHS of the end casing casting but nothing equivalent on the left. Maybe its all a bit marginal in that area. I suppose we will never really know. It will be interesting to see how Colin's box and mod stands up to some hard use.

[LPH_UK]

Why am I reading this thread.....

Just something else to worry about!

[ProtoTipo]

Why am I reading this thread.....

Just something else to worry about!

Leigh, I understand that you have to be very brutal with the transmission, for this to happen.
As Chris Savage has pointed out, a mid engined car does have more 'bite' than a FWD car, when it comes to driven axle grip.
Having said that, I did see an account (only one) on one of the Alfa forums, of a 156 2.5 owner that did exactly the same thing (see Craig's photo above) with a split right round the gearbox casing.

[ByrneEngineering]

Couldn't resist one more video, a quick clip video of the project

https://youtu.be/YSbCe7jHsv4

[NoCorseChris]

I think by far the best mod for the gearbox is the one Neil ended up doing, swap if for an MR2 turbo unit.

[westonTB]

Brilliant vid Colin, especially the onboards. Wish I could get my kids to pass me a spanner!

Looking forward to future rally clips etc.

Cheers!

[ByrneEngineering]

Update video soon, but in the meantime is some of the video of the Stratos @ Targa Tasmania

enjoy!

https://youtu.be/ZYpVOEra3q0