Redrilling front rotors for 1/2"-20 studs

[ZD72novaproject]

Hi guys,

Sorry, not a pro-touring car, but brakes are brakes right! This is a 1972 Nova street car with manuel 4 wheel disc.

We have 15" Weld Draglite Wheels and stock front disk brake set up from Chevelle wrecking yard parts. The rotors are new parts store replacments and we want to run long 1/2"-20 X 3" studs with open ended SST style lug nuts. My son wants that race car look ya know. When I order the new rear end I will get the axles with 1/2-20 studs on a Chevrolet pattern.

I have done a little research and ARP recomends that the hole should be .005 smaller than the knurl diameter in a steel hub and .007 smaller in an aluminum hub.

It is all a little confusing because The ARP specs for some of the studs I am looking at are different than the same ARP part number in the Jeg's catalog. Furthermore, the 7/16" studs listed as replacements are a little different than whats in the car. None of the studs listed show to work with any standard sized drill bit given the .005 interference fit recomended by ARP. One stud is listed with a knurl diameter of .625 which is a standerd 5/8" bit but all things being equil the stud should be loose in that hole.

I would hate to buy a bunch of studs (10) and find out I can't make them work. Does anyone have a part number for the studs they used? Any idea where I could mabey look for replacment rotors already drilled for 1/2-20 studs?

Here are a couple shots of the car the last time it was on the ground.

https://static1.pt-content.com/images/pt/2008/01/186695098-1.jpg

https://static1.pt-content.com/images/pt/2008/01/186695094-1.jpg
Thanks....Steve

[lvrpool32]

This is weird, I have exactly the same question.
I called ARP and they said .005 to .007 under the knurl size (.625 or 5/8), which as you state there is no common drill size.

I spoke to Moser who sell some nice 1/2" wheel studs with a .615 knurl and they state .010 to .015 under for the drill size (so a 39/64 woudl work)

I was curious as to who else had done a similar mod.

Nick

[LarryB]

what I did was take my hubs and axle to the machine shop and had them tap them out to to 1/2 screw in stud an not worried about the knurl
larry

[LarryB]

moroso wheel stud #46200

[lolife55]

For a good press fit like that you will want to use a reamer and not a drill bit anyways. Drill undersize and ream to the final desired diameter. Reamers will be available in the desired size but not something you will find at the local hardware store.
www.mcmaster.com and search for reamers.

[Apogee]

For a good press fit like that you will want to use a reamer and not a drill bit anyways. Drill undersize and ream to the final desired diameter. Reamers will be available in the desired size but not something you will find at the local hardware store.
www.mcmaster.com (http://www.mcmaster.com) and search for reamers.

Reaming or boring is the only way to go unless you decide to go with the 1/2-20 screw-in studs, which is what I would do in your case. Get the ARP #100-7704 wheel studs and drill & tap the rotors 1/2-20, assuming the holes aren't already larger than .453" pilot diameter you'll need.

The thing about drilled holes in general is that they are only good for about .005" to .010" accuracy on the diameter at best, so even if you're lucky enough to have the nominal diameter coincide with what you need, you still can't guarantee that's where it will end up. Several factors will effect the end size of a drilled hole, but suffice it to say, a ream should be good to about .001" or better in the range of diameters we're talking about with good machining practices.

Tobin

[MonzaRacer]

Use a screw in grade 8 allen head 1/2 20 by 4 then cutthem the same length past the nut when exposed as the stud thickness(as required by NHRA) it keeps them looking professional and you can simply put on some of the collored vinyl cap with antisieze inside over them. Oh and if you do have to drill just measure the flat area in front of the raised knurls, make your hole at least that size, if you make it smaller then you need to heat the hub and chill the stud or it will lock up and not pull/push through good.
If you use a hydralic press you will need to support around the hole with a hollow pipe and only have a hole in it large enough for the stud to go through and it better be thick or you can split the cast iron.
and as for press fitting the smooth size to the rotor/hub remember the hub will most times either be aluminum or cast iron and you can trash it if you try to get too radical and you break parts, the stud knurls are supposed to only hold the stud from turning and falling out.
and remeber all studs have a torque spec. Oh and use the silver(nickle based) antisieze on studes too, it doesnt change the torqe specs it simply keeps it from sticking,rusting and galling.

[lvrpool32]

The issue with the screw in studs is that the rear flanges are hardened, so tapping is tough.

[Apogee]

The issue with the screw in studs is that the rear flanges are hardened, so tapping is tough.

I hand-tapped mine a few weeks ago and didn't think it was too difficult. The flanges didn't seem to be induction hardened near as hard as the shafts on most 1541H shafts.

As for using industrial grade socket head cap screws like suggested above, just make sure you use a good quality bolt if you're going to go that route (Holo-Krome for example), as this isn't an item to scrimp on considering what a failure could cost you. The ARP's really aren't that much more $$$ if you're making a Summit order anyway, so there's really no excuse to cut corners on wheel studs.

[ZD72novaproject]

Thanks guys,

A lot of good advice here.

With machine shop and/or tooling (the proper reamer at McMaster is 144.00) and materials cost, I wonder if I could find aftermarket replacment 11" rotors already set up with 1/2-20 studs. Roto-Tech list drilled and slotted rotors in the jeg's catalog but there is no info on the wheet studs. I guess I could call them and ask if that would be an option. Our brakes won't see the kind of repeated hard braking stress you guys put on brakes but I am not sure I want to go with drag race style brakes on a street car. We will put it on the strip a time or two but mostly for tuning. Going to that extreem to save weight is not really what this car is all about. Money is not really an obstacle but I want a system that will be reliable and dependable for a street car without breaking the bank on a high zoot system if possible. Rotor upgrades seem to be reasonably priced but it seems when you go to a rotor and caliper set up the price jumps up to over 1k.

Any advice on replacment rotor options?

Steve

[High Plains Mopars]

Maybe one of these would work.

http://www.speedwaymotors.com/p/2659,191_Wheel-Stud-Drill-Bit.html

[derekf]

Seems like when I was getting everything set up to do a tall-spindle conversion, the instructions specified a metric drill bit to do the wheel stud holes... want to say it was 14mm, but that only comes out to .551 so may not be so helpful.

[ZD72novaproject]

Thanks for all the input. I really did'nt expect such a warm welcome being as this is a street strip car. However, when I found this site it was pretty clear that you guys many times have to re-engineer your stuff to gain the performance levels you are after and that is what I was looking for, free thinkers. As a former Chevrolet Dealership mechanic I spent a lot of time in a front end bay but in that world you just fix whatever went wrong and get paid. This performance/modification world is a lot different so I appreciate any input you have regardless weather I use it or not. So thanks again.

Anyway, here is what I have come up with.

Unfortunatly, screw in studs won't work because the stud holes in my rotors are already .536 diameter. The studs have a knurl diameter of .550 after being cycled in and out of the hub at least once. That gives an interferance fit of -.014 which at least gives me a range of knurl diameter differential that I might be able to work with. The thickness of the hub is .563 and the head of the studs are .745 with not much more room than that inside the hat.

The drill bit posted above is for a knurl diameter of .685 and Moroso offers a stud with a knurl that size. (PN 46190) ARP does not. So problem solved for that dimension. However, there are no specs on the knurl depth from Moroso like ARP has and the size of the head is not stated for either. Most are knurls are around .400 deep based on ARP's specs which I think would work fine but some are .700 which would protrude from the hole in the hub some .137 interfearing with the wheel mounting surface. If the head of the stud is much bigger than .745 or so it won't go into the hole from behind. Both of these problems could be solved on a grinder but I don't really want to do that because it may cause the fasteners to fail and that can't be good. The good news is that the drill bit and the studs combined will set me back about 40.00 so it may be worth that to give it a shot.

I have not begun to research new rotors but any tips in that arena would be appreciated. Attaching the wheels to a car should not be taken lightly so I will continue to study this until I have a comfort level.

Thanks again guys,

Steve

[derekf]

Steve, post up in the "Welcome" forum so we can properly greet you, too.

[ZD72novaproject]

Steve, post up in the "Welcome" forum so we can properly greet you, too.

Will do!