Peter,
I found this in Japan.
Supposedly it is an 'adjustable' clutch pack coupler. The cams inside can be set at various positions affecting how quickly it locks up. It costs about $1300 USD and is actually currently discontinued. I managed to get a contact to talk to the company who provisionally agreed to do a special production run for me. I am trying to get a bit more information about the unit and how it can be set up before I jump on this.
But at this price, the question is whether there is actually any point for this over a clutch pack or ATB centre differential. I presume that when this was developed it was intended to be used with the stock centre open diff and to work in a similar fashion to the Ralliart Viscous Couplings by allowing the rear to kick out farther before locking up and sending power forward.
I am interested in this because I want to see see if it is feasible to use it in conjunction with the Cusco Tarmac Centre differential. The Tarmac diff is a planetary diff that offers a biased torque split 35 front 65 rear. I spoke to a guy over on the DSMLink forums who was using the Tarmac differential and he described it as amazing but frightening. Apparently if used WITHOUT a viscous coupler it offered superb handling up until the point where the rear wheels broke loose because the diff is incapable of sending more than 35% power forwards meaning the car invariably spins out like a rear wheel drive car. The problem with using the unit with a conventional viscous coupler however is that the coupler is constantly fighting against the diff because you are driving pretty much on the edge of the couplers activation threshold (with 65% power going to the rear) all the time. The result of this is that the differential is basically prevented from creating the 35/65 split as intended and causes additional wear on the coupler. Apparently this did typically lead to a 'sweet spot' being created as the coupler became worn or 'loose' and began to react slower, but still fast enough to catch a tail slide.
My intention (if possible) is to setup the clutch pack coupler to kick in at a later stage. I have no idea if this can be done or even if the tarmac diff can turn creating a 35/65 split without causing any wear on the clutches inside and yet still allow the clutches to react if a larger torque split occurs i.e. the rear wheels start to spin. In theory I would think this should work but the physics of it confuses me.
I think the Quaife unit works essentially the same as the Tarmac diff but with a straight 50/50 split. I presume that means it can be used in conjunction with the regular viscous coupler. The cusco MZ clutch pack centre diff allows for removal of the viscous coupler. I don't think it is recommended to remove the viscous coupler when using the stock open diff, the quaife atb centre diff or the Cusco Tarmac Centre Diff. I am however assured that as long as the rear axle has a clutch plate diff on it, removing the viscous coupler should not actually be a big deal as the rear wheels should then be incapable of spinning together unless both wheels were on an extremely slippery surface in which case it is probably game over anyway.
As I said the physics of this does confuse me so if anything I have said is incorrect please correct me or feel free to discuss.
Edit: I also remember someone saying Adam at Devo used to know a place where viscous couplers could be sent to be 'tweaked'. I sent Devo an email but never heard anything back.
