SLC Hubs/ race worthy

Ken Roberts

The modifications to the uprights will probably be around the $500 mark (slotting the three mounting holes and installing a bushing to make it hub centric).
All of the stock C4 wheel hubs and rear stub shafts will be for sale shortly if anyone is interested. (never used)
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Howard Jones

Ken, can I ask why not simply re clock and re drill three new holes like I did? Is it because you have the later sculped uprights? I am not saying you are wrong but I just don't like slots. Please post pictures when you get things back this may be a good solution for the sculped uprights if that is what you have.

It's interesting we are seeing some slightly different dimensions. It's most likely me and my old eyes.

Ken Roberts

Ken, can I ask why not simply re clock and re drill three new holes like I did? Is it because you have the later sculped uprights? I am not saying you are wrong but I just don't like slots. Please post pictures when you get things back this may be a good solution for the sculped uprights if that is what you have.

It's interesting we are seeing some slightly different dimensions. It's most likely me and my old eyes.

My uprights are the sculpted shape. I'm having a bushing installed in the large center hole of the upright. That will make the C7 bearing "hub centric" to the upright. The three bolts are just for clamping force. Slotting of the holes will be inconsequential. Plus the fact the slots are oriented in a radial pattern (pointing back towards the center point of the hole).

The C7 bearing pilot hub is 3.593" verses the C4 bearing pilot hub of 3.620". A .027" difference. I felt that installing a bushing was a good idea since my bolt holes will be slotted. Did you notice the C7 hub pilot was loose in the upright Howard?

My measurements, for the thickness differences, were the same as Paul's. He mentioned 5mm (.197") My measurement was the same. I think you mentioned yours was .24"
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Ken Roberts

I made a PDF template of the spacer if anyone is interested. Make the spacer out of .190" plate. Center punch the 4 holes as shown. Use a 3 5/8" hole saw for the center and three 15/32" holes for the bolt holes.

McMaster Carr has the plate in 6" by 6" size. You'll need two of them

You can send a request (with your email address) to me in a private message. Remember to set your printer to 100%.

Let me get the uprights back from the machine shop and test fit first. I'll post pictures once I get it back to show the process.
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Ken Roberts

Does the DriveShaft Shop give an exchange price on the longer axle shafts? Do you send in the complete axles with CV joints?

Has anyone ever broken an axle shaft or CV joint? I have only heard of them breaking and/or twisting at the 27 spline outer stubshaft on cars with slicks at the track.

Please keep in mind that these upgrades are only needed for cars seeing severe duty.
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Howard Jones

Ken the C7 bearing does have some clearance in the upright hole but not really anymore than the original C4 did. I centered (C7 bearing) it in the upright hole using small equal thickness pieces of shim stock and then used it as a template for drilling the 3 new 13mm holes and then counterbored them and all seams well . It all came out damn near dead on centered.

I think you will be fine with slightly elongated holes as long as their locations are machined properly. The centering ring was a good idea but when you bolt it all together I think you will see just how well the 3 bolts clamp the bearing in place. I don't think the original C4 setup was moving around in any case.

Once I get mine all back together I am going to measure the driveshaft requirement length and then compare that to the ones I have. THEN a call to the driveshaft shop to ask about CV plunge max/mins and go from there. It should be possible to pull the shafts out of the CV's install a longer shaft and reinstall the boots but I haven't really looked into that either. If you go that route mark DS's by side and direction of rotation so that the CV"s will go back on the way they came off. I know my CV's are near new condition I would like to reuse them.

The shafts themselves once used are really not re sellable in my opinion. They take a direction of rotation set and if used again, especially if in the other orientation are prone to fatigue failure. At least that's my understanding.

I am pretty sure the DSS can make you DS's at custom lengths for 930 CV's.

The .24 number was what it took to put the rotor right back in alinement with the caliper. Remember my brake setup is all a one off.

I can't wait to see pictures.
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Ken Roberts

As a quality data point, the stock stub axles are made by The Driveshaft Shop and are of 300M.

I have a feeling that RCR switched over to these DSS stubshafts in 2015. That's when I noticed builders questioning what to do with the stubshaft threaded ends sticking out too far. Apparently they were optional before that year. I'm guessing earlier stubshafts were not 300m steel.

Ken Roberts

I just got my rear uprights back from the machine shop. The fit is very precise. Here are some pictures of the C7 rear Corvette hub installed to the original upright.

The first picture shows how little the bolt holes had to be slotted. You can see the steel bushing that was installed in the center hole for a precise fit.

The second picture shows the hub installed with the custom shim I made. The three mounting bolts have been shortened.

The third picture shows the bolt heads countersunk and the step that was machined at the face for the shorter stubshaft CV flange on the 33 spline C6 Corvette stubshaft.

I ordered the stubshafts but they appear to be back ordered. I will update this post with a picture of it all assembled once it arrives. The bill from the machine shop was just over $1000 (here in Canada) for both uprights. Earlier last week I sold the original C4 hubs and stubshafts for $370. That helped to take the sting out of the machinist bill. I personally think it's worth it for peace of mind. These hubs are far superior to the C4 hub and much cheaper. The 33 spline stubshafts are a lot stronger.
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Joel K

Very nice Ken. I might have missed the main reason for the upgrade, was it more to make your SL-C more durable for track duty or piece of mind on the street? I don’t plan to track my car so not thinking I would attempt this upgrade but just curious.

Ken Roberts

It's a dual purpose car. If I was just building a street cruiser I wouldn't have gone this route. I also get off on the fabricating challenge....;)

Howard Jones

Ken, that came out looking good. Do you have the 33 spline stub shafts yet? I ask because my older uprights don't allow for much re location outboard due to their profile on the inboard side.

But it looks like this thread is getting towards a completion. Several different solutions covering the different upright generations. We just might have a C7 upgrade path for everyone that might be interested. That's what I was going for in the first place. Thanks for your help.

I have my uprights assembled and will put them back onto the car within the next week or so. Then I can get some driveshaft measurements and talk to The Driveshaft Shop. I'll post pictures with them on the car then.

Joel, I had a rear bearing failure at speed running the car at COTA. I run my car on big Hoosier R6-7s and only on track. This prompted me to investigate what had happened and then a possible upgrade path. I (and others) landed on changing the bearing to a much stronger C6 C7 bearing as well as improved stub shafts as a solution.

The front bearings were upgraded for the same reasons although I did not have a failure on the front of the car. However research on racing C4 corvettes and other GM cars produced a similar issue with the stock C4 front bearing. Again this was in a race application.

If you read the thread from the beginning it should become more clear. At this point I don't recommend doing this upgrade on a street only car on street tires that is used within the legal speed limits 99% of the time. I do however have the opinion that either the race suspension should be ordered from RCR from the outset, or a similar upgrade that this thread speaks to be done to a car that is run on slicks and on track.

A street car with huge power (+600 wheel hp) and driven VERY hard A LOT should be considered a candidate as the situation applies.
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Ken Roberts

I can report back that the new 33 spline stubshafts for the C7 wheel hub upgrade fit without any issues. Here are a couple of pictures.


Ken Roberts

Final measurements comparing the C4 to C7 rear hubs (I used a .190" thick shim to space the C7 hub out to the same approx distance as the C4 hub).

Left picture shows the measurement of the C7 wheel flange to face of upright.

difference of .007"

Right shows the measurement from the backside of the upright flange face to CV joint mounting flange.

difference of 1.020"

I now need to have both axles made up approx 1" longer (or use a 1" spacer).


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Howard Jones

So I have concluded my 4 corner upgrade to C6-7 bearings. This is what I posted on my build log but I thought I would repost it here for the sake of completion. This is not cheap to do but in the full context of what is certainly a near 100K track car I think it was relative inexpensive. The good news is this thread has served to explore several options and three different very doable ways to make these changes to the car. Mine for first generation "slab side" uprights, Paul's wonderfully re designed and remade rear uprights, and Ken's really effective re use of the current (sculped) rear uprights. All of these will make the rear of the car as strong as it can be without a complete replaceable bearing type designed upright suitable for WEC full on racecars and the increased cost that goes with that option.

The fronts are a simple replacement of parts with a bit of clearance by hand here and there.

Here's my most recent post on my build log:

So I finished up the front of the car by installing the spherical bearing kit from RCR. Pretty much went together as designed. I like this much better than the ball joint arraignment. The whole thing was pretty stiff because of the stricture in the ball joints. Now the entire front is nice and smooth. The bottom arm moves around just like the top does. Much better in my opinion. I really don't think there is much less effective XYZ travel either.
Here's some pictures of the front complete setup with spherical bearings or rod ends at all positions and C6-7 hub assembles. This is as near I can make it to the race suspension starting with the original street suspension parts.

The rear corners are C7 hubs with top of the line much beefier stub shafts to suit. This is a strong as I can make it with again keeping the original uprights and a arms.

So how much for the whole deal, all four corners?

Spherical Bearing kit (all 4 corners) 1000.00
Front hub adapter kit (pair) 482.99
Front C6 bearings (pair) 559.00
Rear Stub Shafts (pair) 633.98
Rear C7 bearings (pair) 297.00
Drilled Head hard wear 32.76
Machine work 50.00
Machine tools 34.00

Total 3089.73


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Brian Kissel

Staff member
Lifetime Supporter
Howard, Thanks for all the details of this upgrade. Although I’m not building a SLC, this will help on my project as well.
Regards Brian

Howard Jones

The coming year will give me plenty of track time to really give this setup a proper test. I think Paul has also run his car a bit already . So by the fall of 2019 we will have a pretty good evaluation of the merits of the whole thing.

I want to thank a few people: First Fran, We talked a few times about this whole thing and he was the one who first led me on the path of reclocking the rear upright to accommodate the C7 bearing. I have forgotten the name of the other RCR staff member that I asked about the spherical bearing upgrade and I should thank him also. At that point I didn't even know what it looked like and he described how it worked in detail and assured me that it was just really a direct bolt on arraignment. RCR and Fran have been a lot of help to me over the years. He has never given me grief over my sometimes painfully shadetree designs and offered good practical advice when I asked. I could not have done this car without him, thanks Fran.

Paul, Paul and I have spent hours on the phone talking about this whole thing. He offered to try and include me in his one off rear hub project at no financial gain to himself before I realized I could reuse my uprights and I feel like I have made a new friend as result. Good guy!

Driveshaft Shop, It is clear that without the stub shafts they supply this whole thing becomes a whole lot more difficult, custom, and expensive. But beyond that, they never were in a hurry to get off the phone when I was asking question after question about all this stuff. A lot of them about things they don't even sell. The tech department is full of real race car/hotrod guys who know their stuff.

John, He was willing to investigate having a full prototype suspension designed and made for my car. We spent a lot of time talking about this project early on discussing just what I needed and how far my budget would allow me to go. In the end the full racecar stuff just costs too much, at least for me, but the information he provided greatly informed my decision and was very useful.

Ken, kens solution may well be the most useful for the guys who find that they what to consider making these changes. His is a new design and illustrates better than my car what is needed to upgrade a current SLC.

New Braunfels Machine Shop, thanks for the great work for such a good price. I couldn't have done it better, cheaper, or faster anywhere else.

Do you need to do this? If you are running slicks and pushing the car to it's grip limit on race tracks then I would say yes. If you intend to run your car like this and haven't bought it yet then ask Fran about the race suspension option, especially if you want a track only car.

If you intend to build a road car with all the interior and custom streetcar stuff and drive it like you would a Corvette on the street (more or less legally) then I would say no you don't. I also think that the stub shafts currently in use are better (material and strength) than the ones originally supplied with my car. That was about 10 years ago after all.

Somewhere in between? That's what this thread was all about I guess. Only the guy with his hands on the wheel, foot on the peddle, and checkbook in his pocket can answer that one for himself.

What I have LEARNED from all this is what I knew before I started. Race cars are designed STARTING with the tire selected and then everything else is built, selected, and designed to suit them. It's funny how that works, you really don't KNOW something until you DO something. Or something like that...……………………….

Stay tuned for future testing updates from time to time.

Ron McCall

Detroit Speed is now making/selling a hub kit as well for the front.

What (dimensionally) is the difference between the front and rear wheel bearing assemblies? I know that the stock fronts are not drilled and splined but are solid but I noticed that the Detroit Speed front bearing assy has splined holes through the center like the stock rear hub. I wonder if these could be used on either end of the car?
I had my GT-R at the track yesterday for the first time and destroyed BOTH rear wheel bearings in one easy track day! I knew that this was going to be an issue , I just thought I could get away with it for at lease long enough to work the bugs out of the car.


Ken Roberts

The X Tracker hubs are available in two styles. 30 spline with a passive sensor or 33 spline with a active sensor. Ron your stock C4 rear bearings use a 27 spine stub shaft. None of the X Tracker hubs will fit your rear uprights without machining. If you are set on upgrading then the cheapest method is to upgrade to the C7 OEM rear hubs (they are also X Tracker) which have a 33 spline and no sensor. They can be purchased for $95 each instead of the X Tracker which is $250 to $350 each. The stub shafts (33 spline) can be purchased from the Driveshaft Shop. Unfortunately you will also need to increase the length of your rear axle shafts as well by about one inch or use a spacer.

My write up in this thread is for the rear C7 bearing upgrade on the stock uprights. The GT-R and SLC uprights are similar.

Unfortunately the C7 bearings can't be used with any of the adapters (for use in the front).

The adapters can only be used in the front.

There is no bolt on solution for the rear. The 27 spline stub shaft would be the next weakest link anyways. It was only designed to take the twisting forces of production C4 Corvettes. Upgrading to 33 spline is mandatory.

C4 Corvette-27 spline
C5 to mid C6 Corvette-30 spline
Late C6 to C7 Corvette-33 spline

UPDATE-Dulaney has since changed his design so that the C7 front hubs can be used with the adapter at a reduced cost. The C7 front hub does not have a built in wheel speed sensor provision unfortunately if that is needed. The 30 spline x tracker has a passive sensor and the 33 spline x tracker has a active sensor.
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Ron McCall


Thanks for the reply. I am not looking for the cheapest upgrade. I am looking for the simplest upgrade that will provide the desired results.
I am scheduled to participate in the UTCC next month at VIR and after spending two years building this car, I don't want to tear it down and let it sit for months while I work out a solution.