mcm95403

Sadly, the only instructions for this are in a poorly scanned PDF from 1992. There are a few things in that article that aren't clear.

• The biggest of these is the "relieving" that must be done to the knuckles. Yes, you can do it free-hand as the article states but you'd better be strong to hold a high speed grinder in place and not end up making a really ugly cut. I'm not, so both of mine are ugly. Since it will only be seen when torn down it doesn't really matter, but still - if you can pull the knuckles and machine them it would be much cleaner. Doing that would require some sort of jig for a lathe though, so free-hand might be the cheaper way. The easiest way to make that cut is to use a magic marker in the face that the back side of the wheel bearing contacts. Then snap the caliper adapter in place and use it as a guide to center the wheel bearing. You'll see there is a gap of at least .135" between the bearing and the caliper adapter. Press the bearing inwards while rotating it to make a scribe mark in the marker - you now know how much material to remove. In my case it was close to 1/4" and I went .150" deep to allow for uneven cutting and/or expansion.
• Cutting the caliper adapter - what the article doesn't tell you. There is a chamfer on the back side of the adapter that is REQUIRED. Without that chamfer the adapter won't fit flush with the knuckle. There is a very small radius at the base of the raised "tower" that the adapter fits over, so you'll need to make sure your machinist cuts that chamfer when they make the other 2 cuts on the adapter.
• The bolt for the upper trailing arm (on the knuckle) will now be too long to be able to be removed once everything is assembled, so you'll need to insert it through from the inside of the car pointing outside instead. You'll also need and extra washer for the nut - I found that a spare washer from a front brake caliper adapter bolt fit perfectly. The small OD is just right.
• Interestingly, the cotter pin holes in the early axle stub are smaller (1/8") than the later stubs (3/16") so you'll need different cotter pins for those.

On the subject of relieving the knuckles - I had to use a Roto-Zip tool with a special high-speed carbide cutter ($30) with a 1/4" shank that in the SF Bay Area was very difficult to find. A Dremel tool will NOT work to do this. The knuckles may be cast, but they are some very strong, very high quality aluminum and the Dremel bits with their 1/8" shanks will snap off in under 10 seconds. The Roto-Zip does the job well, but WEAR EYE PROTECTION and expect to clean up a LOT of sharp metal shavings that fly everywhere.


Aside from that I have to say this is a really cool mod. I really like the sawblades and really wanted to keep a stealthy, stock look at first glance but have always wanted the big 315's on the rear. This mod was the key to getting that done. It wasn't cheap, but it's the clean way to get it done.


Also, a green pad and some Fast Orange go a long way towards cleaning up the aluminum suspension parts.

ANTI VENOM

Nicely done... Got any pics for us?

mcm95403

Not yet. I should have taken pics while doing the work, but didn't. I do have before pics of the wheels and how much they hung out, so I'll get after pics today or tomorrow.


Today is injector swap and right side header install day.

TA

Looking forward to the pics. It sounds like a cool project.

mcm95403

Pics in Photobucket.


Before the mod:










After the mod:

qwiketz

hi there. I'm not familiar with this mod. So does it just enable you to tuck the tire more under the car? I also have a 92 but I already run a 335 rear tire. I'm the 3rd owner, so I'm not sure if this type of thing has already been done.

mcm95403

This allows for fitting stock ZR-1 offset wheels under 88-96 cars without using flares. If you're going to fit 335's I would expect you'd be using custom wheels so you wouldn't need this.


Effectively, this narrows the rear end .543" on each side so slightly over 1" overall.

ANTI VENOM

I hope you are happy with the results. I think it is perfect now.

mcm95403

It will be once it's aligned and has some negative camber

DanZ51

For those of you too young to remember the Big Doggie mod:

http://aurora40.dyndns.org/misc/C4%2...%20rearend.pdf

aussievetteracer

Probably a little off topic, but just came across this when browsing. DanZ51- your avatar looks like a photo of my C4, taken when I competed in the 1999 Targa Tasmania Tarmac Rally, here in Aus. Where did you get it from? (Obviously somewhere on the net)
Denis

CaptainMerricka

This link is not working for me. Would it work on a 96 vert?

mcm95403

Yes, it would. I still have that PDF. PM me your e-mail address and I'll send it.

DanZ51

Hey Assie,

Yes you're probably right. I found it on the Net some years ago. Another of your Australian vette buddies ID'd as someone he knew (you). I thought it was pretty cool shot.

Aardwolf

95wht6spd

Isn't that called "The Flying C4"?

95wht6spd

This mod would be good to run 12" wheels out back, and not stick out on the later models.

mcm95403

Apparently a lot of guys want this PDF. I'm happy to send it out, but I want to make sure everyone understands that is ONLY done to fit OEM C4 ZR-1 offset wheels under the back of 88 and later C4's - the 84 to 87's can fit them without mods as I understand.

I paid $500 (cheap these days) for the rear wheels, plus another $700+ in parts and machining, plus did all the work myself. It would be smarter to just order a set of Centerline Billet wheels with the correct offset and be done with it. Unless you're trying to keep it all stock-appearing that is.

Anyways, I'm happy to e-mail the PDF to anyone who needs it.

Also, rather than having those spacers machined for the 6 bolts, I’d just thread a die down each one, cut off .300” and clean up the threads. Much simpler. And, if you can machine the knuckle for your bearing on a mill you’re WAY better off. Doing it freehand works, but it’s messy and you’ll never get a nice clean cut.

SECOND THOUGHT on the bolt cutting - I think there is a shank on the bolts that prevents this from being done, so double check that.

CaptainMerricka

thanks for the info. I think I will send my wheels out to be widened instead of trying to find 93 zr1 rear wheels.

mcm95403

PDF attached in post # 18