[Fatzook]

Ok, so I just finished stripping down the SV420 rear diff in readiness for its shortening procedure and few items of note were discovered.

This comparison is between a WT rear axle and the SV420 rear axle.

The axle at the bearing landing is the same size.
The WT axle then necks down and continues at that reduced diameter until about 100mm from the spline were it ever so slightly necks down again (maybe 2mm loss of OD) and then its onto the spline.

Spline engagement appears to be half of the spline length.

The SV axle does not neck down after the bearing, and continues to 100mm before the spline and then gradually necks down to the size of the spline. Spline engagement is also roughly half of the spline length.

Now one thing I find interesting is that the WT spline size and count is exactly the same size as the SV420 axle.

Which brings me to my questions.

Why bother with the thicker axle? (SV420) Surely all they have done is move the weakest point to the end right before the spline?

Does the thicker OD of the SV axle actually help with tortional strength given that it necks down to the same size as a WT sierra axle anyway?

I can appreciate that the SV diff centre/3rd itself is larger in almost every way than a sierra centre/ 3rd, but why bother if the axles are for all intensive purposes just as weak at the spline as a sierra axle ? (assumption)

Now I can apply common sense and logic to these questions and come to the realisation that bigger is better; but why build in redundancies like small splines to ruin a potentially great combo?

Peter

[royce]

in a semi floating setup the axle also has to bear some of the weight of the vehicle and cornering forces, so those being higher in a vit as well as it being longer it would need to be thicker to do this

[Fatzook]

royce wrote:

in a semi floating setup the axle also has to bear some of the weight of the vehicle and cornering forces, so those being higher in a vit as well as it being longer it would need to be thicker to do this

Ok well that partially explains the thickness, but what about the necking down to sierra sized splines? Given that these diff asemblies share absolutely zero parts with eachother I just can't see the point in such a small spline being used.

[royce]

the XL7 is 27 spline
early borg warner from Early Valiants and Fords up to about 75 and jap 4 cylinders were 25 spline
most factory v8 diffs are 28 spline
GQ and GU are 28-32?

hardly small in a 1200kg 100hp small 4wd

[Teracis]

Fatzook wrote:

royce wrote:

in a semi floating setup the axle also has to bear some of the weight of the vehicle and cornering forces, so those being higher in a vit as well as it being longer it would need to be thicker to do this

Ok well that partially explains the thickness, but what about the necking down to sierra sized splines? Given that these diff asemblies share absolutely zero parts with eachother I just can't see the point in such a small spline being used.

Same machine used to machine the ends?

Or something similar, maybe they were thinking about sharing parts and then changed their mind?

[Fatzook]

royce wrote:

the XL7 is 27 spline
early borg warner from Early Valiants and Fords up to about 75 and jap 4 cylinders were 25 spline
most factory v8 diffs are 28 spline
GQ and GU are 28-32?

hardly small in a 1200kg 100hp small 4wd

Well its a small OD fine spline. I'm guessing those V8 axles are larger OD with a coarser spline.

Would an XL-7 hemi fit an SV 3rd? I wonder?

[royce]

borg warner at least is the same spline style
coarser spline isnt stronger either

I am told the center swaps but is there a locker yet?

going full floater? why make the never ending ute build any more complex? full float will be a heap stronger anyway

[Gwagensteve]

The guys that I know of with largish vitaras seem to break axles a fair bit.

I don't think they are particularly strong, but I don't think it matters where they neck down - only that they do - sierras and vitaras break their axles in the same spot - at the spline.

Fatzook - I don't think adding one spline is going to make much difference. Improving the material the axles are made from is the real key as far as I am concerned.

Steve.

[Fatzook]

royce wrote:

borg warner at least is the same spline style
coarser spline isnt stronger either

I am told the center swaps but is there a locker yet?

going full floater? why make the never ending ute build any more complex? full float will be a heap stronger anyway

Yeah going full floater. I'm fitting the shortened SV gear for now with full floater setup. Alsready cleaned the housing of brackets and started removing the bearinghousing from the drivers side. Taking 150mm off the tube and jigging/ re-welding in place. Then I will have the new axles made to suit full floater bits. Since the axles and machined floater bits are being machined by other people it shouldn't slow the build down at all

[Teracis]

Gwagensteve wrote:

The guys that I know of with largish vitaras seem to break axles a fair bit.

I don't think they are particularly strong, but I don't think it matters where they neck down - only that they do - sierras and vitaras break their axles in the same spot - at the spline.

Fatzook - I don't think adding one spline is going to make much difference. Improving the material the axles are made from is the real key as far as I am concerned.

Steve.

Isn't the number of splines just to distribute the load across more splines? More would be good to a point and then you would get back to the individual splines being too weak?

[royce]

FWIW of the 8? axles Jeff broke in his GV, only 2 were at the spline, perhaps its only once age and wear is a factor that they let go there?

[Fatzook]

Gwagensteve wrote:

The guys that I know of with largish vitaras seem to break axles a fair bit.

I don't think they are particularly strong, but I don't think it matters where they neck down - only that they do - sierras and vitaras break their axles in the same spot - at the spline.

Fatzook - I don't think adding one spline is going to make much difference. Improving the material the axles are made from is the real key as far as I am concerned.

Steve.

Yeah spline count was not my main concern. Its more the diameter of the shaft AT the spline. Which like you said is where they brake. Perhaps the extra girth across the bulk of the axle reduces deflection due to load as Royce suggested, given that they are semi floaters.

The new shafts will most definately be of a higher grade steel. No sure what yet....

[Fatzook]

royce wrote:

FWIW of the 8? axles Jeff broke in his GV, only 2 were at the spline, perhaps its only once age and wear is a factor that they let go there?

Yeah rightio So my fear of necking down the new axles like the OEM ones is fairly irrational then

A mate has a hardness tester. I might pay him a visit with some axles and see what results they produce. Atleast then I may have some chance of estimating the % increase in strength the new axles have.....

[royce]

I dont think hardness comes into it, a file is hard but doesn't take to well to being twisted

you need a 'strong' material but it also needs to have some movement in it to absorb a bit of shock

google up axle info for aftermarket 9" axles, usually you'll find a lot more easy to understand info relating to relative material strength

[joeblow]

[Gwagensteve]

Quote:

One vehicle has most of the gear reduction in the t/case, and the other has it in the diff. The vehicle that has the gearing in the t/case should use an axle that is thicker, both in spline and shaft. The vehicle that has it in the diff can get away with smaller diameters as the torque laoding on the axles will be less.

I'm not trying to pick a fight, but think this is wrong, and I'd like you to prove your reasoning here Joe.

Your position that load leads to be shared between axle and transfer is fair and reasonable, but AFAIK, once you get to the axleshaft it doesn't matter where the reduction has come from - the torque has already been multiplied.

100NmX3.65gearboxX5.1transferX4.1diff=7630Nm at the axle
100NmX3.65gearboxX4.1transferX5.1diff=7630Nm at the axle

Please explain how the axle sees a different torque load in the second example.

The point about autos is interesting though. When we've broken stock rear axles it's generally been the result of a bounce. Autos are much kinder to the driveline, especially when landing from a bounce, as there's give through the converter.


Steve.

[royce]

you can get away with less axle strength when the reduction is at the hub, IE portals, not the diff center

[got_bar_work]

Just another reason for Joe to make portals.

[Gwagensteve]

Quote:

you can get away with less axle strength when the reduction is at the hub, IE portals, not the diff center

Absolutely.

Steve.

PS - whilst it is theoretically quite easy to make bolt on portal boxes, some of the engineering involved gets quite complex. There's no way a sierra housing is strong enough to support the leverage, and scrub radius becomes a huge issue.

I have a couple of VW portal boxes sitting in my shed from when I was all excited about portals, but the scrub radius problems really killed it. Have a look at the work Mark's adapters have put into their portals for patrols to work out how hard it is. It's possible, and quite possible that Joe could build them, but I'm not convinced it's a great idea.

[Fatzook]

joeblow wrote:

I will now get something off my chest. Refering to upgraded axles as 'chromo' is very missleading. In fact all good axle material can be called 'chromo'.

Well Joe I find THIS^^^^ comment even more misleading, as upgraded axles can and are produced in many grades of steel and steel alloys, but only one series can be called 'cromo' (CRMO).....

Definition for chromoly:
41xx steel is a family of high-strength low-alloy steels (HSLA), as specified by the Society of Automotive Engineers (SAE). Alloying elements include chromium and molybdenum, and as a result these materials are often referred to as chromoly steel or CRMO source

1014-1018 steels seem to be popular upgrades for 9" diffs. But i've not seen them refered to as cromo yet.

[mondo]

1014-1018, i would consider that a very soft steel, what is standard? .

[Fatzook]

mondo wrote:

1014-1018, i would consider that a very soft steel, what is standard? .

As royce said, its not all about hardness. Torsional strength is a much bigger concern ( axles ability to twist)

Perhaps using 1014 accompanied by an increase in diameter IS considered stronger?

I had not started looking into grades as of yet, more the design/ machining aspects.

[Ridge]

Pete with your plans for the rear axle build, will you legally be able to run a larger tyre then +15mm over stock?

[Fatzook]

Ridge wrote:

Pete with your plans for the rear axle build, will you legally be able to run a larger tyre then +15mm over stock?

I'm still working through that. So far it looks like the only way to get past that rule will be to certify the ute as an ICV (individually Constructed Vehicle) which would require a very large amount of work, as the entire car would have to meet current ARD's.

My engineer will lodge the case appeal anyway to see if QLD transport will go for the 'everything is upgraded so why not?' approach; although I am not getting my hopes up.