Working on a side project. I have an old street rod type truck with a C4 suspension. The current rear suspension is a '94 model year unit, but for better fender clearance I'm considering putting the slighly narrower early knuckle assembly on it. Under a layer of dust on the shelves I have a couple '84/'85 knuckles and a couple (short looking) stub axles that have the ABS rings on them. Just guessing, but perhaps these are '86 type axles when ABS was introduced IIRC. Anyone know off the top of their head if the ABS type early axles wil fit in the non-ABS knuckles?

Just looking for information before I go through all the motions of finding and cleaning stuff up to try to assemble everything to see if there's interference due to the ABS rings (and possibly have to trade/buy the non-ABS axles for this project).

Thanks for any help.

Knuckles are '84 & '85 then '86 & '87, spindle is also '84 & '85, then '86 & '87

Yes, the numbers are different but I think dimensions are the same on 84-87. If you remove the tone ring from the 86-87 stub axle then I would say that you get a 84-85 stub axle. I also think that the tone ring would clear the 84-85 spindle.

(Bolded above) That is my hope. I've got a semi-useful wheel bearing gathering dust too. I think I'll try to assemble all the pieces this weekend and see if there's any clearance issues. AFAIK, there's no great demand for the ABS type stub axles compared to the earlier/original design axles, so I don't think I'll be "ruining" an expensive piece in the event I end up pressing the ring off.

Thanks for the info and part numbers.

You'll certainly be able to confirm!!

*** So in your particular anticipated use you'll sacrifice the disc only rear and revert to 'shoe in rotor' eBrake?

I'm not terribly concerned about any ebrake issues. I can't remember the last time I used/needed an eBrake. If I change my mind down the road, I'll just transfer the later caliper onto the revised setup.

I don't believe it's easily accomplished and even to use the early knuckle/spindle arrangement I believe you'll need to use early hardware, backing plates, rotors and caliper etc! There was a modification that wasn't inexpensive to narrow the later. I believe that modification maybe was just over 1" total, a bit under .6 inch per side. It was used to put 11" @36 offset under '88+ C4.

Information was never out there in very practical 'format.

https://www.corvetteforum.com/forums...ng-rearend.pdf

I only have the parts for drum style parking brake so I can't compare.

What we know:
* Half shafts are the same.
* Wheel bearing hubs are the same.
* Early stub axles are shorter from u-joint to bearing hub. ( reducing track width )
* Mounting position of the bearing hub must be closer to the axle by the same amount.

What we don't know is exaclty what changed regarding to the last point.
Are early and late caliper mounts the same thickness? From pictures I don't think the early are that much thinner, if thinner at all.
Are the mounting face for the caliper mount in a different position on early and late splindles?
Is it possible to mount the late caliper bracket on an early spindle, and what would that do regarding to track width? At least we know that the bolt pattern is the same.
Toe links are the same. Upper and lower dog bones are the same. Camber rod has a different part number, so you should probably use the early one with early spindles.

Actually I think the early drum brake is better because it just works. I have head lots of problems with the automatic adjustment for the caliper maunted parking-brake. ( no personal experience )

According to this from "big dog" modification the stub axles for 84-87 are identical except for the tone ring.

Well, making some progress and learning a few things. I have most or all the parts to mock up the setup I'm interested in. I didn't have a spare late C4 rotor, so I had to take that off the suspension under the truck to use during this exercise. I bolted the early setup together (knuckle, caliper mount and wheel bearing) and then installed the reluctor ring equipped spindle. Works okay, no ring interference. I then put the rotor and unbolted caliper on to see if there was any wheel interference (I'm using the 15" Corvette wheels on my truck). While doing this I noticed that these rotors are 12". I had totally forgot about that, as I've got the earlier 11.5" rotors on my '69. Everything seems to fit.



Next item was to actually bolt up the caliper. Chevrolet had the good manners to keep the mount spacing the same as the earlier calipers. It seems wise to keep as many things consistent as possible, in case there's a quality/availablity/durability problem, and the option to use older parts as service parts. (I'm reminded that there's probably more than coincidence involved that the C3 batwing has the same bolt pattern as the earlier iron differential cover.)

I scrounged up some old pads and put them in the caliper, and then slipped it over the rotor. Due to the difference in rotor depth/offset compared to the early rotor, there would need to be a half inch spacer between the caliper bracket and the knuckle tabs. No big deal, darn near a bolt on setup.



Well, while running some longer bolts through the setup to test for rotor/caliper clearance I noticed the first actual issue to be solved. When the caliper is correctly/adequately spaced above the rotor, the centerlines of the caliper bolt hole and the knuckle mount hole are vertically off by roughly .050-.100 (just eyeballing it). At present the caliper cannot be dropped down far enough to get the bolts threaded in. This issue requires one of several remedies:

1) Grind some rotor clearance in the caliper bracket to allow the caliper to drop down. (Hate to do that.)
2) Machine about 50-100 thousandths off the rotor OD. (Cost money, as I don't have a lathe.)
3) Reclock the caliper, and make an adapter bracket between the caliper bracket and the knuckle mount. (BTDT. Works, but is a bit time consuming.)
4) Weld-up the knuckle anchor holes and redrill them .050" higher. (Reasonably easy and painless.The leading candidate at the moment.)

So, that's where I'm at presently. I have one additional item I'm curious about. Are all late C4 rear rotors 12", or are there 11.5" rotors out there?

Well, I missed on the chart Joby supplied that the '84 caliper mount is different from the '85-'87 mount. I found out when I noticed that the '84 caliper mount ears are drilled for smaller bolts than the '85-'87 ears. Looks like I have an '84 left side caliper mount and an '85-87 mount on the right (the setup I grabbed and used for the pictures). In the end it shouldn't be a big deal, as I need to weld up and redrill the caliper mount bolt holes anyway.

What's the thickness difference between the 88-up caliper mounts and the earlier style? Visually looks like the earlier one is a bit thicker.

Both the knuckle and the caliper mount are thicker on the later pieces.

Can you get a measurement of the thickness of each? Then we would know how much of the width-differance that comes from caliper mount and from spindle. A simpler "Big-Dog" might be early spindle with late caliper mount.

The early caliper mount is about 1 13/32 inch thick, while the later mount is 1 9/16 inch thick, for a delta of abour 5/32 inch. The later knuckle looks to be about 1/2" longer from the trailing arm mounts out to the caliper bracket mount surface, compared to the earlier knuckle. So, it appears that both the knuckle and the mount are longer on the later suspension.

The early pictures you provided shows that putting the late mount on the early knuckle would present several issues/problems. The centering counterbore on the late mount is noticeably larger than the early part, requiring either the caliper mount inner centering bore to be welded up and machined to match the earlier knuckle centering flange OD, or the early knuckle centering flange would have to be welded up on its periphery and machined to match the larger ID of the later mount. There would also need to be additional machining on the caliper mount to arrive at the correct width/depth so that the stub axle would correctly fit inside those pieces.

That's the picture I'm seeing here. I welcome your comments and input.

Since this is under a 'chassis' that isn't a C4 wouldn't be practical to just move the brackets for the knuckle supports, shorten the 1/2 shafts, fabricate lower control arms and modify the the toe assembly that will likely be an issue anyway. That would let you 'customize/modify' width as much *** you like. In many 'rest-rods' that use C4 that's the accepted modification in nearly all cases. Put your wheels where you like for panel clearance and create the rest using what you already have assembled. Upper shock mounts usually don't present an issue when used in 'other than' C4 chassis.

I did the bolded mods above when I put a narrowed C4 suspension under my '69 a bunch of years ago, but all that effort and expense(!) isn't necessary for my street rod as the target suspension width is the same as a production early C4.

Well, played around some more with this setup, and it looks like things ought to go together pretty well. I got overly curious the other day if everything would actually bolt together if I just reduced the late rotor diameter about an eighth of an inch on the radius. I don't have a lathe, so I just sanded about .100" off an arc portion to allow the caliper and steel bracket to drop down further on the rotor. Did that, and with a 9/16"-5/8" spacer between the caliper bracket and knuckle mount ears, it all bolts together. And fortunately, looking at the pads it looks like they're positioned within the friction surface ring of the rotor.

My earlier reluctance to do some lathe work on the rotors was based on a couple things: I don't have a lathe (or the skillset to use one), and I hate having to contract out things that end up costing me money. While doing some early fab work on an adapter bracket a fellow C3 owner contacted me offering to do this lathe work for a price I couldn't turn down (free). As I'm going to be busy a chunk of this winter's free time pulling the engine out of my '69 to replace the cam (posted in another thread), the street rod truck will be on the back burner. But in the off moments I'll be searching to see if there are any off the shelf rotors that would meet these dimensions. (Kinda close dimensions below.)

I presently have an early C4 suspension under my '69. If Chevrolet was gracious enough to keep the steel rear caliper bracket consistent over the C4 model run I suspect I could use the rear rotors off the '69 and be able to bolt the late caliper up without any spacers. (However, I could also be wrong.) If the early rotors work (my concern is where the late caliper pads sit on the rotor friction surface due to the smaller radius) I could pilfer those rotors off the '69, and use this as an excuse to put lighter two-piece rotors on the rear of the '69 (I have two piece rotors on the front presently). The only issue here is that I haven't seen two piece 11.5" rotors (matching the early C4 size), so I may have to do some changes to the caliper bracket, as I'm presently running Wilwood calipers on those rotors, and the nearest two-piece rotor is 11.75"