I was able to do some work with these rear brakes today. I have now confirmed that the 2 things I was concerned about in the rear are indeed both an issue. these 2 things seem to be the only problems left with this whole install.
the first obstacle is very easy to overcome & not much of an issue, other than raising costs a bit. the rear parking shoes are about an inch smaller in diameter than the current fx parking brake. all this would require is for Joe to substitute loaded backing plates for the naked ones, raising the costs here by a few hundred or so... the only good thing about this is that now it's sure that performance rotors will become available soon as the rotors are exactly the same as the g37s. had the parking brake been larger & these were proprietary to the fx alone, it may have limited performance rotor availability for at least some time
the second obstacle is the only real problem with this whole retrofit at this point. so far the fronts are fine & the rears are almost there after throwing enough parts at it. the only real problem remaining is the upper ball joint... the hole for the upper ball joint in the new knuckle is much larger than the existing ball joint . from an engineering point of view it's obvious as to why they changed this. the original knuckle was cast steel. cast steel has a very hard surface strength, so even with a 20mm tapered down hole, it is hard enough to resist deforming of the ball joint hole under in service stresses, but the new knuckle is cast aluminum. had it been cnc'd billet aluminum it may have been hard enough to go with the existing ball joint design, but cast aluminum is relatively soft. that same narrow tapered shaft would have a much higher chance of deforming the hole under in service stresses. by enlarging the hole to a 35mm severely tapered hole they have more than doubled the contact area of this hole, & more than doubled it's available surface hardness at this joint, making it as strong as the previous design & as strong as it needs to be.
not to worry yet, there are several possible solutions to this last problem & I'm sure we can get this to work. 1 is the possibility of also swapping the upper arms. it is sure to fit the knuckle & solve this hole problem, but it is not certain that the arm itself will fit. without crawling under a new fx I'd have to give this a 50/50 shot at best. the rear suspension on the new fx is very similar to the old, but there have been some tweaks to the suspension geometry too... the sway bar also happens to attach to this upper arm too, if the new upper arms do bolt in & complete this whole retrofit then I would say it is still very worth it & would probably be the best way to go, but I'm guessing that will add over $400 too, & that's over & above the add'l costs of the parking brake now
option 2 would be an adequate solution I think & should be much more cost effective, & that would be to have a bushing/adapter machined that would allow the early 20mm tapered ball joint to fit the late 35mm tapered hole of the new knuckle. this bushing would have to be precise & it would have to be very hard... think billet steel or maybe even cast & machined stainless... I'm sure a high end cnc machinist could build these at a respectable cost but they've got to be 100% correct too. as long as it's precise then it is the equivalent of the correct ball joint & the cheaper solution. this may also require a new custom ball joint nut to be able to maintain the use of the safety cotter pin. I think that a custom machined adapter setup like this is very possible & may be the best practical solution if the upper arms weren't an option, & should be much cheaper than the upper arms. I can work with Joe & help develop this adapter
at this point these are the 2 best options to pursue. a third option of just having the too large hole welded closed & then re machining it to fit the smaller ball joint shaft exists, this would be the average hot rodder way of doing it, & truth is it may very well work out just fine, but once you understand why they enlarged this hole to begin with you realize the drawback to that approach & why it is less than ideal.
