another cheaper option for the people wanting to go LSD

[Gly]

So, I need to find an STR / Type-V rear diff casing and shafts.

BTW - Gly, are you also Glycerine?

yes you do, complete unit as you use the STR/Type-V crown and pinion.

and yes i am. i take it you found my post on the evolutionm forums??

[MunkyWrench]

this seems the right place for the info to end up:

The Open diff from the Non AYC VR4, or STR is what we are after, but what about the other lesser 4wd models.
Do the 25ST or GDI 4wd models have this same differential?

According to this they are the same for ST, ST-R 1.8ST and Viento 4wd:

Legnum Viento 2.4 4wd


Legnum ST (1.8GDI)

Legnum ST-R

---

We need the casing (including the input flange), ring and pinion, and shims/ bearings that get retained when fitting the LSD to be same as the STR listings.

The diff casing is the same part number,
so is the carrier assembly, (and the shims, bearings blah blah bunch of other stuff...)
so is the final drive gear set (see "34084 GEAR KIT,RR DIFF FINAL DRIVE"),
and the flange is the same too (I could imagine this being different for a lighter drive shaft in the more gutless models).

At this point I have over thought it I am sure.
Other than the flange, there is no reason for any of this to be different once we confirm the case, carrier assembly, and gear set are the same.



Please stop/correct me if I am wrong, or reinventing the wheel.

There is a Viento 4wd wreck nearby so I might pick the diff up out of that. Save on some shipping.

[scott.mohekey]

They are one and the same. Adam is using a casing out of a 25ST of mine.

[MunkyWrench]

ta. the only differnece i found is that listing shows the ST, Viento as having a dynamic damper and a bolt presumably for it. STR doesn't have it atleast not on that listing. Done deal.

[Gly]

yep me and kenneth pulled one from a GDI Viento as spares, its exactly the same.

make sure you get the shafts to as they are needed for the conversion

[Adam.Findlay]

I broke the ST-R diff during my RWD escapade. removed the lsd cartrage from the blown ST-R casing and dropped it into a Viento diff and works fine.

[Davezj]

when the standard AYC diff breaks what part of the case breaks and what is the rotation action that actually does the breaking.
i was thinking rather than replacing the ayc diff could it be strenthend to stip it breaking in the first place, via so additional bracing or bracketing.

[Adam.Findlay]

when the standard AYC diff breaks what part of the case breaks and what is the rotation action that actually does the breaking.
i was thinking rather than replacing the ayc diff could it be strenthend to stip it breaking in the first place, via so additional bracing or bracketing.

has beed done on one of the evo forums. however to brace the stock AYC casing he had to remove the inner workings of the AYC and ended up replacing the guts of the diff with a cusco plate lsd anyway, so no point, why not just get the strong diff casing to start with and put the good lsd into that.

anothe guy also CNC'd a billett alloy AYC casing for strength. but im unsure if that ended up staying AYC or just ended up taking a plate diff cartrage also

[Davezj]

Up to this point I have never considered the diff needs to upgraded to run high power.
I am just interested in how the diff case fails.
Is it the twisting motion along the axis of the drive shaft that just cracks the case leaving the internals in tack, or is it some of he internals going bang and exploding through the case.
If it a twisting/stresses on the case that cracks it then ensuring the case can not twist via some extra bracing and bracketing, could possibly stop this failure occurring.
Does anyone have any pictures of failed/cracked diff cases with a reason for failure, just so w can see if it is preventable.

[Davezj]

Here is another little thought,
The str has a super strong and heavy rear diff case, but it has a light weight alloy front sub frame which is not super strong.
The vr4 has a alloy light weight rear diff case, but has a heavy pig iron front sub frame which is supper strong.

This seems wrong, but I am sure mitsi had there reasons.

[Adam.Findlay]

Up to this point I have never considered the diff needs to upgraded to run high power.
I am just interested in how the diff case fails.
Is it the twisting motion along the axis of the drive shaft that just cracks the case leaving the internals in tack, or is it some of he internals going bang and exploding through the case.
If it a twisting/stresses on the case that cracks it then ensuring the case can not twist via some extra bracing and bracketing, could possibly stop this failure occurring.
Does anyone have any pictures of failed/cracked diff cases with a reason for failure, just so w can see if it is preventable.

As with any gear system with a ratio, the input torque does not equal the output torque. and the casing must make up for this
in this case our diffs have ~3.33 ratio i think. so for the propshaft putting in 100 Nm torque there will be a output or 333 Nm across both output axles (half shafts).
so 100 in 333 out gives a difference of 233 Nm difference (ie holding torque)this must be taken up by the gearbox/diff casing.. the more torque you put into this system the bigger the holding torque becomes!
thats why often you see drag cars ripping the diffs clean out of the subframes, as the torque difference applied to the diff casing becomes too great and it just twists the mounting bolts off the diff/ subframe.
Also i think with diffs. because its a 90 degree drive. the input is trying to twist the diff along the axis of the length of the car, and the output is trying to twist the diff along the cars width. so input =/= output so the diff has to hold not only the input torque but the output too, not just the difference between the two.

this is why the cast iron diff casing is better/ stronger. even though the gears inside may not be any different to AYC gears. these casings do not deflect/warp/bend as much as a soft alloy casing would.
Ayc fails due to the casing flexing which cases the gear teeth to not mesh properly, casing much higher loading on the teeth (bending moment at the base of the teeth which results in greater stress in the material) ultimatly leading to failure (teeth smashing off) and in some cases the casing can split clean in half
although hard to determine the exact failure. my ayc diff split into 3 different pieces and stripped 2/3 the teeth off the pinion gear. Im not sure if the casing split from the broken teeth jamming between the gears and forcing the casing apart or it split of its own will.

I think the front subframe difference is because the vr4 requires much more rigididy as the twin turbo will put alot more force on the chassis compared to the N/A but thats whole other kettle of fish, suspention nonsense

[Adam.Findlay]

hope that makes sense and answers your question

[Davezj]

that is a brilliant answer.

i just have to digest it and mull it over to see if i can work out what direction the forces are going in and see if there anything that can be done.
i will probably not do anything with it, but i like to sit down an work things out and find a potential solution, it is only then i realise i don't have knowledge/skills or money to implement that solution.