sam@neatgearboxes

AYC and Super AYC variations - debunking myths and misinformation

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This is based on our experience, not on hearsay. We're not claiming this information is exhaustive, but we're fairly sure we've got the information right on this. If anyone can point out any other variations we're not aware of or not covered here, please feel free to let us know so we can add it in (as long as it can be backed up with evidence).

We hope this information is useful to the community.

 

Early AYC (Evo 4-7) have a finer tooth count on the crown wheel and pinion (with a very slightly different ratio); and the gear cutting process is face milling (arguably not as strong as hobbing). The gears from the later SAYC are interchangeable. The main weakness in the early AYC is the housing - it uses a smaller ID carrier bearing on the clutch side, the housing is thin in this area and prone to breaking. These diffs came with an open 2-spider diff centre which is also quite weak.

 

Late SAYC (Evo 8,8MR,9) gears have a coarser tooth count and are manufactured using the gear hobbing technique. The Aluminium housing is thicker in key areas, particularly around the carrier lug. This corresponds with a larger carrier bearing on the clutch side. The diff centres are helical LSD units and are fairly strong, as well as providing better traction characteristics than the open centre in the earlier AYC.

 

I have determined no difference between the 8, 8mr and 9 SAYC diffs internally, although sometimes it's difficult to know what model the diff is out of in the first place.

 

Cheers,

 

Sam

Edited by sam@neatgearboxes
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Hi Sam,

Is it possible to fit later SAYC diffs to the 4-6? Obviously the RS diff is preferred but not always easily available or affordable. 

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I'm sure one of the mechanical workshops on here will be able to answer this for certain (we don't work on vehicles at all!) but my understanding is yes, they are completely interchangeable.

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thank you and great example of a vendor going the extra mile to support the community

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I do my best to provide correct information based on my findings only but cant guarantee its validity at this time as I havnt personally tested an Evo X rear differential; neither RS or AYC. 

 

With that said................

 

To add to this discussion, I have read that Evo X GSR AYC rear differential is also interchangeable with the notion that the pinon to prop shaft flange is swapped to a 4-9 bolt pattern(which are inter-compatible).   You could otherwise drill them out to suit the prop-shaft.

Evo IX differential into an Evo X
http://www.evolutionm.net/forums/evo-x-engine-turbo-drivetrain/715859-help-evo-x-rear-diff-swap-evo-ix.html

Considering the RS differentials are cross compatible, it'd suggest Evo 4-9 and X AYC rears differentials are interchangeable with the appropriate mounts.

As for the Evo X AYC rear differential, castings appear identical visually but whether there are differences within in those units is beyond me but perhaps someone else can chime in on this and the compatability.  There are no mention(online) for ring and pinion swap required which implies theyre the same ratio*(edited in) within the evolution AWD family - dont quote me on this.

A link to some photos an Evo X GSR AYC rear differential and its associated internals for interest.
http://www.jackstransmissions.com/collections/rear-differentials/products/evo-x-rear-diff-rebuild

 


 

 

derku

Edited by derku
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