Drilling Rotor Hat for Larger Studs

[sjaroslo]

As some of you may know, I am replacing/re-doing the rear brakes on my project to correct some questionable stuff done by the build shop. I won't belabor that point too much here. Anyway, after spending a lot of time trying to get back to the place I was before, I have come to realize that the wheel studs on my axles are slightly larger than the holes provided in the Wilwood hat. Wilwood actually addresses the situation in the instructions, stating:



"NOTE: Some OEM and aftermarket axles come with stud sizes larger than 0.50” diameter. Verify stud size and have a qualified machine shop drill the hats to the correct size, if necessary."

My question is, is there any harm in me drilling these out myself? I do not have a drill press, so it would be free drilling with a cordless drill. But, the current holes are around .5", the studs measured out at .53", and the previous shop looks like they drilled the old hat out to about .55"--so we're only talking about going from 1/2" to maybe 9/16" at most--actually, a 14mm bit looks like it would be the closest match to what the old shop had done, which fit fine....

As always, thanks for the advice.

[Rod]

the stud holes aren't that precise, the rotor hat is centered from the hub center (both front and rear) drill away

[jpgolf14]

the stud holes aren't that precise, the rotor hat is centered from the hub center (both front and rear) drill away

I agree with Rod. The centerbore should be centering the rotor, not the stud holes. In fact I'm shocked the existing holes are to small. Personally I like things that fit tight and would probably drill it pretty tight. Problem is most drill don't won't very well when enlarging a hole slightly. There are special bits specifically for this job like core drills and reamers. It depends how fancy you want to get.

John

[sjaroslo]

I agree with Rod. The centerbore should be centering the rotor, not the stud holes. In fact I'm shocked the existing holes are to small. Personally I like things that fit tight and would probably drill it pretty tight. Problem is most drill don't won't very well when enlarging a hole slightly. There are special bits specifically for this job like core drills and reamers. It depends how fancy you want to get.

John

Thanks for the quick replies. I don't really want to get too fancy but your comment about drills not being very good at enlarging a hole slightly caught my attention--any suggestions on how to deal with that? Is a shot of WD-40 on the hole a good idea?

[jpgolf14]

Thanks for the quick replies. I don't really want to get too fancy but your comment about drills not being very good at enlarging a hole slightly caught my attention--any suggestions on how to deal with that? Is a shot of WD-40 on the hole a good idea?

Yeah when you use a normal drill to just barely enlarge a hole, they tend to catch, drill off center, and produce a poor quality hole. For what you are doing I'm sure it will be functionally just fine, just probably not all that pretty and not a lot of fun to drill, especially without a drill press.

Lubricant is not a bad idea, but will probably not do much to help the catching issue. If your rotor hats are aluminum, WD-40 actually works quite well. If they are iron, no lube is necessary.

My suggestion is to use very low pressure until the drill starts to cut. Once the hole is started, it should cut ok.

An even better idea is to chamfer the hole before you drill. That will help the bit start and stay centered.

[NOT A TA]

I'll add to check the wheel studs for a taper that may require a chamfer on the inside of the hat anyway.

[gort69]

Just to confirm the hole size isn't that important because the rotor registers on the axle. This is an early 4th gen Camaro rear disc setup on a 5 on 4 3/4 first gen axle - note how big the holes are. I believe this rotor fit more than on application so they just made the holes big enough to fit either. I have since swapped out the rear discs for the later 4th gen setup (LS1) and it is much the same. Have run both for many miles w/o issue.

[sjaroslo]

You can see here that the base of the wheel studs are just ever-so-slightly larger than the threaded portion...
Attachment 69329

They are so close that indeed the threaded portion fits through the hat no problem, but the base of the stud does not; it is difficult to see here but the hat is standing proud of the axle flange...
Attachment 69330

Now I know what the small ring that was in the packaging is for--the hats that the shop used were an exact fit around the axle stub, but these are larger; the ring included in the kit fits perfectly to a counterbore cut on the inside of the hat and the ID perfectly matches the OD of the stub. I wonder if I can stick that ring to the hat with a dab or two of silicone seal to keep it from falling out during a brake service somewhere down the road...?

I'm really shocked about gort69's photo--while I understand that the rotor can't jiggle up and down because it registers off of the stub, it still seems to me that the rotor could rotate back and forth with the application of the brakes--enough cycles of that and I would think that potentially dire circumstances could ensue! But that's just me being a worry-wart, I'm sure....

[Rod]

I'm really shocked about gort69's photo--while I understand that the rotor can't jiggle up and down because it registers off of the stub, it still seems to me that the rotor could rotate back and forth with the application of the brakes--enough cycles of that and I would think that potentially dire circumstances could ensue! But that's just me being a worry-wart, I'm sure....

the rotors will not move with the clamping force of the 5 lugs at 110 lbs each, (just being safe on the torque) some axle or cars require more

[Apogee]

...I'm really shocked about gort69's photo--while I understand that the rotor can't jiggle up and down because it registers off of the stub, it still seems to me that the rotor could rotate back and forth with the application of the brakes--enough cycles of that and I would think that potentially dire circumstances could ensue! But that's just me being a worry-wart, I'm sure....

Like Rod pointed out, so long as your wheels are properly torqued, your rotor should never be free to move...if it is, it means your wheel is moving as well and you're probably going to be breaking wheel studs shortly. Your wheel studs should be in pure tension, so don't let the idea that your rotors apply any side loading or shear to them get any traction in your head, because they don't. You're much better to err on the side of extra large clearance holes through the rotor than too tight and have them not seat entirely when you torque your wheels.

Tobin
KORE3

[MrQuick]

As some of you may know, I am replacing/re-doing the rear brakes on my project to correct some questionable stuff done by the build shop. I won't belabor that point too much here. Anyway, after spending a lot of time trying to get back to the place I was before, I have come to realize that the wheel studs on my axles are slightly larger than the holes provided in the Wilwood hat. Wilwood actually addresses the situation in the instructions, stating:

"NOTE: Some OEM and aftermarket axles come with stud sizes larger than 0.50” diameter. Verify stud size and have a qualified machine shop drill the hats to the correct size, if necessary."

My question is, is there any harm in me drilling these out myself? I do not have a drill press, so it would be free drilling with a cordless drill. But, the current holes are around .5", the studs measured out at .53", and the previous shop looks like they drilled the old hat out to about .55"--so we're only talking about going from 1/2" to maybe 9/16" at most--actually, a 14mm bit looks like it would be the closest match to what the old shop had done, which fit fine....

As always, thanks for the advice.

I like to use a step drill...Although its not necessary, if you don't mind the drive you are welcome to use my drill press.

[MonzaRacer]

WD40 SUCKS to drill with, you want to burn up bits, use that.
My preference is synthetic motor oil in squirt can. Since I am a tech I can drain Mobil 1 cans at work BUT also I used Mobil 1 in my 350 roller after swapping in the roller cam. BUT for tapping and drilling I do prefer synthetic oil. Thicker the better, but thats me. I had a set of Snap On Thunder bits that I used to drill wheel studs out with when lugnuts came in stripped and not coming off.
As for hand drill, no big just be careful and make sure you have it clamped down good.

[jpgolf14]

WD40 SUCKS to drill with, you want to burn up bits, use that.
My preference is synthetic motor oil in squirt can. Since I am a tech I can drain Mobil 1 cans at work BUT also I used Mobil 1 in my 350 roller after swapping in the roller cam. BUT for tapping and drilling I do prefer synthetic oil. Thicker the better, but thats me. I had a set of Snap On Thunder bits that I used to drill wheel studs out with when lugnuts came in stripped and not coming off.
As for hand drill, no big just be careful and make sure you have it clamped down good.

Actually, WD40 is quite good for aluminum. It is worthless on anything else. The op's hats are aluminum.

In aluminum you are not using oil to absorb heat, rather you are using it to reduce the aluminum's stickiness. It is basically impossible to burn up a HSS bit in aluminum since the coefficient of thermal conductivity of aluminum is so high.

[sjaroslo]

Thanks for the continued feedback on this. I do not think that the hats are aluminum because they weigh a ton and they have the integrated parking brake drum but now my curiosity is piqued so I'll have to see if Wilwood lists the material.... I picked up a 9/16" bit from Home Depot so I'm hoping to make some time to give it a shot this weekend and I'll report back.

[Skip Fix]

Might double check the hats that they are the exact diameter as the axle pilot AND the pilot is ong enough to register and locate the wheel.

For me clamping the rotor in a drill press with C clamps and using a bit to locate the existing hole exactly, then drilling with larger bits. You can get a decent small drill press that can do the job for not alot of money.

[sjaroslo]

The material is cast iron:

http://www.wilwood.com/Hats/HatProd....temno=170-9492

I've decided to have a shop take care of this.... The temptation is great to pick up my own small drill press but it will totally become a dust/spider collector for the rest of eternity. Hope to drop them off on Friday. Of course, I wish that I had figured this out before I bolted/safety-wired the rotor on to the hat, but I'm hoping that isn't really going to cause an issue for a shop to deal with. If so, *sigh*, I'll cut the wires and unbolt the rotors from the hats and go that route. I'm fairly damned proficient at safety wiring at this point!

[astroracer]

Just drilled these 'vette rotors out for the van this past weekend. Took all of two minutes with the 1/2" Milwaukee and a .563 dia. bit.


These register on the hub so there are no worries about the lug hole size. They slip on nicely over the 1/2 studs we put in the hubs.
Mark

[sjaroslo]

Nicely done, sir!

[Munster]

If I didn't know I hadn't taken the pics I would have thaught sjaroslo had come in and taken pics of my problem. Same exact problem, collar on bottom of stud larger than stud hole in rotor. Read the thread, remembered I had a step bit, when it was mentioned, and within 5 minutes I was back to assembly and a lot happier. Spent two hours before that trying to figure out what in the hell was wrong. My rotor has a good tight fit on the hub centric so I feel confident drilling out the stud holes. Its nice to have a place to come and trouble shoot and get good info. Now back to the garage.

[sjaroslo]

That is indeed one of the many awesome things about this forum. the amount of intelligent and thoughtful help available is really amazing.