my new KYB GR-2 strut cartridges arrived the other day, so i started mocking it up while i'm waiting for my brake parts to arrive. something i finally realized once the parts were in my hands is that the choice of this particular cartridge has nothing to do with its dimensions; in fact, dimensionally its shit: its body and inner shaft are way too short for the hugely long 412 strut body. long spacers/adapters are needed to effectively use it. the whole idea behind using it is its valving: perfectly suited to the spring rate and weight bias of the 411/412.
aside from the diameters of the outer body and the inner shaft, its altogether too short to use without a specially machined extension fitted to the threaded inner shaft and a roughly 3" long spacer inserted under the cartridge body inside the strut tube to bring its height up flush with the top it (the "strut tube", or "body").
a member of the 411/412 forum posted some images that he rendered illustrating these; the extension "stub" can be clearly seen at the end of the threaded inner shaft, and the silver bit at the other end is the lower spacer:
i dont have the upper extension made yet, but here you can see the lower spacer i made with 1 3/4" pipe:
lined up with the cartridge body:
as it sits without the lower spacer:
with lower spacer:
it was a little too short, so i added an old Litespeed titanium (!) integrated headset cup insert to bring the face of the cartridge just above flush:
with the collar screwed on, the basic assembly looks like this:
piece by piece, the upper assembly looks like this... upper spring plate:
bushing/spacer (which effects spring preload):
strut bearing (same on late 412s as certain super beetles):
the rubber bearing seat/damper (again, a super beetle part):
the strut bearing plate:
and finally, the top cap and nut. since the upper extension hasn't been added yet, the threads dont protrude above it, so ignore that detail, for now:
once i have the dimensions for the extension i can have a machine shop fab it for me, then assemble everything. on these particular strut bodies the lower spring perch has been machined off with the intention of relocating/welding it on 1-2 inches lower on the strut body:
although this mod wouldn't effect ride height, it would preserve the stock amount of spring preload once the completed, shorter strut cartridge is installed along with the appropriately modified upper mount.
the biggest hurdle in this process is modifying the actual body of the car to accept this assembly. the shock towers, or rather the body of the car itself (its unibody) is engineered to accept a very specific design of upper strut assembly; namely, not what i intend to fit. on top is my car with the early-model "symmetrical" mounting, late-model "asymmetrical" on the bottom:
the plate bolts in from underneath with the dome poking out into the trunk. on the older style this was all bonded rubber, like you can see in the top pic. these were poorly designed and all died at a young age...even NOS ones (if you could find one) are dead by now just from age, regardless of mileage or use. luckily the last year of the 412 used the same upper assembly as the super beetle, and parts are very available. the newer style uses a conical rubber donut under the dome as a bushing, a part you can still get new today (if it wears out. it wont). so the donor struts that i'm doing this work on came from the '74 412 fastback i parted out a few years ago and had the late-model super beetle-style strut plates.
the issue is that the big center hole in the body that the dome of the strut plate pokes through is too small on my '73 to fit the '74 plate by just under an inch (~20mm), not to mention the bolt pattern. in order to use the superior, late-model strut plate/bearing assembly that hole has to be enlarged and new holes drilled. the uber-genius Ray Greenwood from the 411/412 forum has posted an acceptable-sounding way around this problem by using a combination of early- and late-model parts. this is probably what i will do, the less grinding i have to do on the body the better. but i cant really do anything until i have the extension stub made, so i guess i'm back to waiting for parts for the time being.
i'm actually leaning towards slamming the bastard... i'm kind of over doing things the "proper" way...i want something that looks kick-ass...but if i dump the front end i will definitely have to arrange a rear end lowering situation...i dont want a Starsky & Hutch look...much.
