So folks, I'm a (gasp!) Legnum VR4 owner who has an S-AYC rear diff fitted to my car for about 5 years. It's basically a drop in replacement for AYC.

Last week, it obliterated itself. Rear wheels locking when turning, groaning, pinging, all sorts of horrid sounds. I got the diff out today and wow, the planetary differential just consumed itself. Pic attached, plus a link to a short YouTube video here:
I guess I'm curious how common this is, and if it happened to you whether you just replaced the diff assembly and kept everything else. My ring and pinion look mint still, which is amazing considering that a couple of teeth ejected themselves from the differential housing into the main diff casing.

 

I'm curious and concerned now, too. How much power does your car make? Are you using an Evo 8 or 9 ACD ECU for control?

 

The car is 500hp at the crank, about 400 at all four wheels on an Australian "Mainline" brand chassis dyno at Transformance Mechanical Engineering in Sydney, Australia.

The car still uses the stock VR4 AYC controller. Comparisons of the programming tables betweern the AYC and S-AYC controller have been made and they are identical. It would be impossible for the controller to destroy the mechanical differential, as the mechanical side is, well, mechanical, and the AYC side is just speed gears which alter the rotational output speed of each side of the differential, hence creating a torque bias.

Also I just want to reinforce this is the AYC rear diff we're discussing here not the ACD center diff.

 

Ooooh, any chance you have a rom or disassembly of the AYC code available to be shared? I think ROB808E has now fully figured out the AYC routines in the 8/9 roms but I think he still might be interested in seeing the control development over the years (even if the maps are the same). FWIW 8 & 9 are the same but don't recall about 7. I think that the solenoid current max limit on a late model 9 is raised but otherwise there are no map changes (at least from what I recall).

I didn't really think that some imperfect control of the clutch packs would be able to cause the obliteration, but copious engine torque, a strong differential torque and plenty of grip might be beyond the diff's limits? I think I've read about at least one high HP drag Evo blowing an S-AYC diff here on EvoM - hopefully someone else will chime in on that.

 

I suspect it was caused by a launch or two. I have Michelin Pilot Sport 4 tyres fitted *and* a helical front LSD. What used to happen was that most of the torque got sent to one of the front wheels which would lower the shock a bit, but with the front LSD there is less ability for the load to be sent anywhere but all four wheels.

I'll ask my friend Bill who owns the ozvr4.com forum and is also the guy who disassembled the ECU ROMs for the VR4, allowing stuff like E85 flex fuel tables. He may have been the fellow who analysed the AYC config tables and ROM.

 

Well I've done some digging on this part and apparently it's in huge demand. At least in Australia, I am not the only person to blow an S-AYC diff.

 

from what i understand, this is the reason everyone who races eventually switches to a pure mechanical

 

Amazingly I found an entire diff local to me. Price was...acceptable.

 

Because I love tuning my ACD ECU, the hill I'll die on is that the S-AYC is too cool to swap to an LSD. Kaldek, you've just made me decide to buy a spare when I find one (if the price is ok). Glad you found one.