Ok then whats the verdict,
What do we have to do to make this safe?
I don't think it's possible to make a frame to go along the transmission tunnel as per the MX5 unless you widen the tunnel. My son is going to be the first passenger so i need to get it right.

Johno

Simple, 6 bolts 2 brackets and a ford diff :D

I spent some time looking at this and noticed that all the broken beams I have looked at on the net <dozens of them>are broken on our nearside . That I reckon it is due to the diff being mounted on the offside and when the diff is loaded its putting the beam on the nearside under a lot more pressure. A bit like a tripod with unevenly spaced legs. That brace gadget thing I saw spreads the diff loadings at the nose of the diff evenly. Just a theory I will keep eating the toblerone

Bob

I don't think you have anything to worry about Johno, if you are worried still use steel for the tub back and make sure you have and inch of play at the gearbox end of the propshaft. That's what I'm doing anyway! And test first without child. :D

Robo they are design to fail on that side.

Well all I can say is something needs doing, the yanks have dealt with the problems with the braces. In normal hairdressers mode the car probably has no issues but these things are going to get a spanking and as the mx5 fails so will the roadster version. Needs looking at.

bob

Mx5 diff
 

I have just noticed something, I dont know if it is that important but if you look at the saturns/nts mx5 build guide revision 3 page 30 you will see the diff in the car. If you look closely you will see two very small cut outs notches top and bottom on the right hand side of the ally casting, if you look at nathans post you will see that the diff broke at this point. I know it broke because of other reasons and this has probably nothing to do with it, apart from this being a bit weaker. I have not checked my diff yet for these marks, just thought I would mention it.

http://forum.miata.net/vb/showthread.php?t=349293


http://t0.gstatic.com/images?q=tbn:A...pnBhU7U06neswg

There is a mod. worth reading. A frame that bolts the diff to the gearbox. What I dont understand is that if mazda fitted this as standard on some cars called a ppf <and they break> how come they have they have been omitted in the roadster builds.

Bob

Yep, that's the Mazda designed in safety point, designed to break at this point in an accident so the PPF doesn't pierce the fuel tank. It is a built in weak point.

TK

Bob

The PPF frame is standard to all mark 1/2/2.5 MX-5s (not 100% sure about the mark 3, but I would be surprised if it's different).

It's essentially an ali C section beam (about 5mm material thickness) that is hard mounted to the diff nose via 2 x 8" bolts. The beam runs alongside the prop (and covers the O/S side of the prop) and is hard mounted to the gearbox tail, again with 2 x 8" bolts. It's worth noting that the PPF is the only mounting on the front of the diff. The only compressible mountings (AFAIK) are the diff ear rubbers and the engine mounts on the front subframe. Therefore, any rotational movement about the driveshaft axis will be affected by the moment of the engine/gearbox.

As an aside, I read on miata.net that Mazda say that if the rear upper top hat washers are removed, they render the PPF scrap.

It might also be worth seeing what sort of upgrades Flyin Miata or Performance 5 do for the rear diff area (FM have built a 800+bhp Miata and offer lots of tuning bits).