NTS MX5 Build

[Big Vern]

Did you not have the diff side bolts fitted? (where the power plant frame bolts up)

[jenks]

Is it just me or does looking at the photo of the point of failure and actually reading Nathan's description of what happened / how he mounted it, make it clear this had nothing to do with a need for extra triangulation, 'girders' or any modification to the diff cage at all!!! The thing snapped a diff IN HALF before having a chassis failure!!!

What actually happened in this case, if you fit a winged diff just by running a bolt through the crush tube directly the mounting point the load is completely suspended by the rubber bush with no limit in travel... Put a large turning force through it, one wing is pressed hard up against the chassis while the other is pulled down hard pulling / flexing the bush as far as the rubber part will stretch... This can only go so far before something goes crunch!

If you mount the diff with no caps on the bushes, even on the original MX5 subframe and and drive it hard will pull itself to pieces...

The fact it wripped a diff in half and didn't budge the diff cage plates proves Andrews design is sound... Just make sure you fit the thing correctly with no missing parts

[MarkB]

Originally Posted by jenks

Is it just me or does looking at the photo of the point of failure and actually reading Nathan's description of what happened / how he mounted it, make it clear this had nothing to do with a need for extra triangulation, 'girders' or any modification to the diff cage at all!!! The thing snapped a diff IN HALF before having a chassis failure!!!

What actually happened in this case, if you fit a winged diff just by running a bolt through the crush tube directly the mounting point the load is completely suspended by the rubber bush with no limit in travel... Put a large turning force through it, one wing is pressed hard up against the chassis while the other is pulled down hard pulling / flexing the bush as far as the rubber part will stretch... This can only go so far before something goes crunch!

If you mount the diff with no caps on the bushes, even on the original MX5 subframe and and drive it hard will pull itself to pieces...

The fact it wripped a diff in half and didn't budge the diff cage plates proves Andrews design is sound... Just make sure you fit the thing correctly with no missing parts

I would imagine the rear frame work is twisted after the forces needed to snap a casting like that have been put through it.

[shh120m]

Originally Posted by MarkB

I would imagine the rear frame work is twisted after the forces needed to snap a casting like that have been put through it.

Not at all mark, everything is still square, no cracked welds, no stress fractures just a bit of scratched powdercoat.

The rear casting on the mx5 diff is actually pretty poor in terms of stregnth, it weighs less than 1 kilo and when inspected, there are large air bubbles within the alloy, you could drop one from less than a meter and shatter it to bits. The only ones that are stronger are the smooth cased castings used on some of the early viscous diffs which are crap in comparison to the torsens, they are rare as rocking horse shit though, iv heard of the drift boys paying £250 just for a case to fit to locked torsens

[Big Vern]

Originally Posted by shh120m

Not at all mark, everything is still square, no cracked welds, no stress fractures just a bit of scratched powdercoat.

The rear casting on the mx5 diff is actually pretty poor in terms of stregnth, it weighs less than 1 kilo and when inspected, there are large air bubbles within the alloy, you could drop one from less than a meter and shatter it to bits. The only ones that are stronger are the smooth cased castings used on some of the early viscous diffs which are crap in comparison to the torsens, they are rare as rocking horse shit though, iv heard of the drift boys paying £250 just for a case to fit to locked torsens

As I stated in my earlier post, have you not mounted through the fixings on the side of the Iron part of the diff assembly where the PPF mounts to? This is the strong part of the diff - the two rubber mounts on the wings are just to stabilise side to side motion of the powerplant assembly which in the donor vehicle is two rubber mounts on the engine at one end and two on the diff at the other end. If you mount the diff only through the rubber mounts then you'll just keepp tearing them out.

BV.

[shh120m]

Yes as per chassis design

[Big Vern]

Originally Posted by shh120m

Yes as per chassis design

I have looked at your design, it doesn't use the diff side mounting system the same way as the donor. You have just a bit of plate with an ex engine mount. The diff is therefore free to 'wobble' around on the rubbers under torque. To work you'll have to mimic the power plant frame to diff mount, on the chassis. All rubber mounted diff is never gonna work, the rubbers would have to be very stiff, shore 95+ or something similar. The westfield system is much more robust and they still cracked diff housings.
The diff to power plant frame is the main fixing for the diff.

BV

[Davidbolam]

If you look at the mnr chassis this is mounted in a similar way to the nts/saturn version and it seems to work for them. I am sure that once the plates are on both sides of the rubber mount this won't happen again. Here is a picture of the mnr version. The westfield version also seems very similar. Both of these only seem to use the front mounts ( in the steel section) to stop this rotating forward and backwards.

http://www.google.co.uk/imgres?q=mnr...QWG9cAK&zoom=1

[MarkB]

The MNR works because it's a mass of triangulated tubes not open rectangles/squares, that and Marc Norden knows how to grow onions

[jenks]

Sorry @MarkB , I don't see the logic in your posts at all... Are you saying this diff failure wouldn't have happened if the diff cage / chassis was further reinforced? Not trying to be offensive, I'm just not sure what you're trying to get at!

Can understand the need for more rigid mounting on the nose of diff but the overall cage / rear frame design and support of the diff wing has nothing to do with this failure. The tortional forces on the wing bushes are nothing compared to those on the nose mounts. Use the correct bush caps, mount the nose properly and diff won't dismember itself.

A more contructive input would be telling everybody where you think this additional triangulation needs to go (?)