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Rear Stud Repair and Upgrade (without removing hub)
Just before Halloween, my left rear wheel fell off. I had a few seconds warning, and managed to slow down a bit. The wheel stayed in the wheel well, and the parking brake shield seems to have carried most of the weight of the car. One stud was sheared off, the others bent. All lugs were missing. I could have borrowed a few lug nuts from the other wheels to get home, but the remaining studs were really bent, so I got towed home on a flatbed.
I'm not really sure what happened. But it seemed a good opportunity to update my studs.
I'm splitting this into several posts, to try to avoid the Forum's recent login timeout bug.
There was no shoulder on this 55 mph highway, so a bit of a harrowing place to stop. Any further, and I would have high-centered at the edge of the ditch.
Last edited by Bikespace; Nov 18, 2023 at 11:05 PM.
The tow truck left my car in the driveway on a free block of wood. Step one was to get the car into the garage. I ended up cutting off the most bent stud, then hammered two more straight enough to use, and rolled the car into the garage on wheels.
A few years ago, I sent my trailing arms off to Bair's to rebuild. They did a great job, and I cannot fault them in any way. But I can fault my own prep work, and hope that my example might help someone else.
What I should have done before I sent my trailing arms to Bair's was to follow @GTR1999's best practices for attaching the rotor to the hub, and then insisted that Bair's bolt on the rotor, and let me do the final shim. Instead, they riveted the rotor onto the hubs, and turned the rotors down a bit to zero out runout. That's fine, and for most folks, all you ever need. Again, they did a GREAT job, and I would highly recommend them if you need C3 parts rebuilt.
I contacted @GTR1999, who confirmed that this was a repair I could do without taking apart the hub. I knew I wanted to use ARP 1/2" studs. Here's what he suggested I do.
Originally Posted by GTR1999
If you are going to ARP then you need to measure the axle flanges, rotor hats, ARP knurl length and overall stud length you want and machine the studs. That's how I do them but they're also apart so I can work with the axle and rotor separately and match them.
Before you do anything check the runout and endplay in each one. If you have under 003" runout thru 360* that is good and you want to keep that. I would be very surprised if you have over 002' runout, you actually shouldn't have any with a rotor that was machined after riveting. You should not have any lateral play. If you press on the rotor are 3 & 9 you shouldn't feel any movement or rocking in it. If you grab a wheel stud and feel movement in/out that means there's at least 003" endplay in the bearings. It is still in spec but I wouldn't ship one with over 0025" runout or 0015" endplay.
Once you have your base info, you can remove the rivets and the rotor. Mark the relationship and side they came off. In order to replace the studs you have to see if there is any place with a gap large enough between the back of the axle and backing plate, I doubt there will be. Some guys drill a hole in the backing plate to allow the old stud out and to install the new ones. Again if going to ARP you better have all the measurement and machining done.
Driving out an old stud can be done with a hammer but I never liked that since it is hammering on the bearings through the axle. One of those tie rod tools may work to press out the old studs. A Lisle stud tool will pull in the new studs, that's what I use now and what you will need if the axles are still in the bearing. You can use a couple of nuts with grease too but the tool works better.
Deburr around all the rivet holes once you get them out,same for the studs holes. Countersink the back of the rotor hat holes too. If you are using new rotors, make sure you check the parking brake shoes fully collapsed. I buy my ss parking brake hardware from Bairs but never use it as it come out of the bag. I always machine the starwheels shorter and fit the other parts. I have had new rotors, both NAPA and "HP" slotted and drilled rotors come in with the hat ID too small. The rotors are too large for my lathe so I have to set them up in my Bridgeport and bore them larger.
To install new ARP and rotors and do it right, takes time.
Anyway, before I can do anything else, I have to drill out 5 rivets, and remove the rotor. I used a center punch on the rivets, and drilled them out. I think I only missed the center on one. You can see the gold paint pen I used to mark the hub (and rotor).
Last edited by Bikespace; Nov 18, 2023 at 09:50 PM.
As it turns out, my parking brake was non-functional. The retainer pins were bent, the springs and washers were twisted and floating around. I cut the remaining springs blindly and removed the shoes. The actuation lever could not be removed, so that gave me the access hole I needed. I removed the 4 bolts that hold the splash shield, and cut around the actuation lever. That gave me the slot I needed to remove the bent studs, and punch out the remaining rivet backs. I followed @GTR1999's advice, and pressed the studs out with a ball-joint tool (pictured in Post #6 below).
Last edited by Bikespace; Nov 18, 2023 at 11:09 PM.
So, speaking of oversized studs, @GTR1999 also gave me instructions on how to turn down ARP studs in a lathe, to shorten the knurl area, and to cut them to length. That's great! But I don't have access to a lathe. So I found something that would work with no modifications to the stud.
I bought a set of ARP 100-7705 studs. I read all of the descriptions, and chose these because they are 1/2" diameter (obviously), have a short knurl area the same length as the thickness of the C3 hub flange, and are just the right length to fit behind my 18" wheels with a 2" adapter (not a problem I have yet, but I problem I hope to have by the spring, and I already have the wheels). So no lathe work needed! I can make mods to the rotors and hub flanges instead.
Unlike what @GTR1999 uses, these have a WIDE knurl area. ARP says they need a 43/64" hole to catch the knurls correctly. That's a bit of an odd size, but I bought a drill bit. But what took a LOT of time was drilling out the hub flanges by hand. I used my whole collection of step bits to get close (5/8", after starting at 7/16"), then finished with the 43/64" drill. I also had to use my deburring tool from the outside of the flange, since I couldn't chamfer the exit hole on the inboard side. It turns out the wider hole was helpful, though, as I didn't have a straight shot at the back of the flange, so the studs had go in at an angle through the notch in the backing plate.
I used the Lisle stud installation tool, and the new racing lug nuts to install the studs. I oiled the stud for installation, making sure to clean the oil off with brake cleaner at the end of the project.
Last edited by Bikespace; Nov 18, 2023 at 10:33 PM.
Installing that one stud to make sure this was going to work was not the best idea, as it got in the way of drilling the remaining holes. It also got in the way of tapping the rivet holes for bolts. It turns out the holes were just about the right size for 3/8-24 bolts (as specified in @GTR1999's instructions, at the link above). I chamfered the holes, and tapped them with the kludgey drill arrangement below. A 1/4" 12 point socket fit the tap. When I test fit the rotors with 1/2" holes, I saw that I needed to drill them out a bit more to avoid scraping the threads. And for once I could reach both sides of the hole, so I opened them up to 9/16", and chamfered them. I then installed the 3/8-24 bolts, and checked the rotor for runout. Near enough to zero, so I put the caliper back on, and connected the swaybar.
Last edited by Bikespace; Nov 18, 2023 at 10:42 PM.
I put the wheel back on, removed the screw-in dust protector from the new lug nuts, and installed the wheel. Then I torqued them to 100 ft/lbs, since they are bigger than stock. If anyone has any thoughts on this number, please let me know.
On the table, are just some of the tools I used, plus the studs and nuts for the other rear wheel. Of special note are the step bits, which worked great (drill bits, not so much). If I do the other side, I'll try to find a step bit that ends in 5/8". The 5/8"-9/16" wrench once belonged to my grandfather, along with the oil can. He was a machinist, so it was pretty cool to be able to use his tools to work on my car. That wrench is the ONLY tool I have that can remove the caliper bolts, even with the sway bar removed.
Here are links to the parts used, if anyone wants to try this at home. Please ask any questions, or kibbitz my torque setting!
WOW- I know that feeling - as I lost a knock off wheel on my C2. I was stopping for a light and it just kissed the inner fender lip and took out the shield.
Just some thoughts,
1- I think I would have spotted a hole in the plate rather than cut away the PB lever.
2- Looking at those sheared studs is concerning. Bair's uses "TR" stock studs and I have used 100's of the same without any issues- for stock drivers. It's good you stepped up to the ARP and those you selected will certainly work. But my concern is that is a stock GM axle. If the applied load is enough to shear the studs, you may be on borrowed time with the GM axle as well. They usually hold up well compared to the new stock axles sold today. Some of the new axles, imported, break in street use. The last imported axle I tried to use I got directly from Pat Ikerd, so you know that was a long time ago. I stripped the threads off it torquing the nut to 100 ft/lb. It was 1 of 2 I bought and never attempted to use imported axles again. If you are going to push the car, I recommend you go to the best - not the knockoffs sold today, but Tom's 31's. They are still being made and sold, they setup differently than stock and that info I no longer share, since some out there took advantage of info I offered over the years. I will say, they have to be machine fit. I have never seen a set of real 31's break. I have seen and have in house some of the knock offs and they're junk.
Obviously, a lot depends on how you use the car and your power, trans, & traction.
Just some thoughts,
1- I think I would have spotted a hole in the plate rather than cut away the PB lever.
Thanks Gary!
I thought about that. And if I had a lift, I probably would have done it that way. I chose the expedient route that let me work from jackstands, and kept metal shavings out of my hair. And the parking brake was already broke, so I didn't change that.
Originally Posted by GTR1999
2- Looking at those sheared studs is concerning. Bair's uses "TR" stock studs and I have used 100's of the same without any issues- for stock drivers. It's good you stepped up to the ARP and those you selected will certainly work. But my concern is that is a stock GM axle. If the applied load is enough to shear the studs, you may be on borrowed time with the GM axle as well. They usually hold up well compared to the new stock axles sold today. Some of the new axles, imported, break in street use. The last imported axle I tried to use I got directly from Pat Ikerd, so you know that was a long time ago. I stripped the threads off it torquing the nut to 100 ft/lb. It was 1 of 2 I bought and never attempted to use imported axles again. If you are going to push the car, I recommend you go to the best - not the knockoffs sold today, but Tom's 31's. They are still being made and sold, they setup differently than stock and that info I no longer share, since some out there took advantage of info I offered over the years. I will say, they have to be machine fit. I have never seen a set of real 31's break. I have seen and have in house some of the knock offs and they're junk.
Obviously, a lot depends on how you use the car and your power, trans, & traction.
So I don't recall touching that wheel in 6 months. The one stud sheared off, but it may have been the only one holding the wheel on at all. No other lug nuts were found, so it is possible they loosened and backed off, or pulled off the studs.
Rear Stud Repair and Upgrade (without removing hub)
