Some of the SL-C builders who are tracking their cars were blowing out their rear bearings. The stock C4 bearings and 27-spline stub axles are OK for street use, but they are not suitable for a SL-C on racing slicks (forum discussion here). While Superlite offers a racing upgrade for the suspension it’s not suitable for the street. In mid 2019 Superlite began shipping cars with new uprights, C5/C6 bearings and 30-spline stub axles. In addition to being more robust, the new hubs have integral reluctors which are an improvement over the reluctor rings that I had previously installed on the CV joints. Specifically, everything is enclosed and there is no need to fabricate custom sensor brackets which might get knocked out of alignment.
Fortunately, Superlite offers an upgrade path for existing cars like mine. The upgrade comes with the following; two uprights, two spacers, six stainless steel dowel pins and two stub axles. Unlike the previous generation uprights which were handed, the new uprights and spacers are symmetrical and can be used on either side. I wasn’t sure what the two 7/16”-14 holes where at the top of the uprights so I called Superlite. Apparently the new upright is the same as the one used on the GT-R which uses cross bolts for the top billet piece. So what might have been four different upright parts, is one. In addition, the use of a spacer allows a thinner piece of aluminum to be used for the upright which reduces material costs and machining time. This was a smart change.
The pictures below compare the older right rear upright (on left, part# SLC-RR-UR-01R) to the new upright (on right, part# SL-RR-UR-02RL).
Right rear uprights as viewed from inside the chassis; old on left, new on right. The front of the car is to the left.
Right rear uprights as viewed from the wheel; old on left, new on right. The front of the car is to the right. Note that the new upright has the spacer mounted using dowels in the three smaller holes.
Right rear uprights as viewed from the front edge; old on left, new on right. The 1/2” thick spacer is mounted to the new upright which makes the new assemble ~0.2 thicker than the old version. I had drilled and tapped holes for the parking brake bracket when this picture was taken.
Superlite forgot to send me the dowels, so I ordered some from McMaster (part# 90145A541). The first step is to insert the dowels into the uprights (light taps are all that’s needed). As mentioned above, the uprights are symmetrical so you need to insert the dowels into the side that faces the hub/tire. Once that’s done, the uprights are handed. The spacer can then be placed over the dowels and lightly tapped until it’s flush with the upright.
Another benefit to the new version is that it’s easier to drill and tap holes for the parking brake brackets. As can be seen in the pictures above, there is significantly less pocketing in that area than the old version and the middle web is ~0.91” (~23 mm) thick which easily accommodates M10 screws. I used the DRO on the mill to drill the holes, but I used layout dye and a micrometer to prevent another D’oh. Measure five times, drill and tap once. Following the 2x thread diameter rule of thumb for aluminum I drilled the holes 25 mm deep and used a M10-1.5 bottoming tap.
I bought SKF Corvette Racing Hubs from TPS Motorsports with pre-installed ARP studs. According to their website:
The SKF Corvette Racing Hub unit is designed to provide high stiffness during cornering, thereby reducing piston knock-back and the need to tap the brakes (confidence tap). It has <10 micron run-out and is designed for durability and to maintain preload at sustained loads of 1.2g!
Six M12 - 1.75 mm thread x 75 mm Socket Head Cap Screws and six M12 washers are needed to mount the hubs to the uprights. I’m not sure what comes in the new kits, but McMaster only had that length in iron oxide so I spent a bunch of time looking for zinc-plated ones. The smallest quantity I found was a box of 80, so if anyone wants some PM me and I’ll ship six to you at cost.
I drilled the socket head cap screws so that I can add safety wires when the car is finished. The hub can be clocked in any of three orientations and I positioned it so that the wires would be as close as possible to the parking brake. This keeps them away from the primary brake caliper and enables me to run those wires with the electric parking brake wires. The reluctor wires are very close to the stub axle and there is no provision to keep them in place. I’ll figure out how to affix them once the parking brake brackets are machined.
I wasn’t able to mount the upgraded Brembo GT two-piece rotors to the hubs because the holes machined in the rotor hat by Superlite have a very tight tolerance (a good thing). I assumed that the longer studs were slightly askew so I opened the holes a little. I found that that a 31/64” bit fit the holes perfectly, so I used one to locate each hole on a drill press. After clamping the rotor to the table, I used a 1/2” bit to open the hole and then a counter sink to chamfer the edge. While not a complicated process, I also chamfered the other side so in total that’s 20 hole locating and clamping operations, and 50 bit changes! I was able to get the rotor to fit by tapping it with my hand which caused the threads to create a few shavings. My bit set only goes to 1/2” so I’m going leave things tight for now.
I’m waiting for some parts to be plated (e.g., the ball joint plate, lower shock pins, etc.), so I haven’t mounted the hubs to the car yet, but I’m not expecting any issues.
Note that I didn’t upgrade the front uprights and hubs because, as discussed in a previous post, I had already upgraded the front hubs to re-buildable race hubs which are much nicer than the SKF racing hubs. Unfortunately they are no longer available.
