RR w/11" drums and 7/16" studs

VitaminCRR · Aug 9, 2020

Hey all. New member and first post. Just bought a 69 Roadrunner, a driving project. I put DrDiff discs on the front and found out that my original wheel studs were 7/16x20 in 11" drums. The DrDiff studs are 1/2" so no big deal for the front but how will I get 1/2" studs into the rear axles? From what I'm seeing the stud knurl diameter is .475 (or so) so a 1/2 stud wouldn't fit in that hole. Do I need to drill out the axles to put 1/2" studs back there? I'd rather not have to use two different size lug nuts on the front and rear. Any ideas?

VitaminCRR · Aug 9, 2020

I'm looking/searching other sites and I'm finding out that the axles shouldn't be drilled. Mostly cuz you can't drill them straight enough. I think I'll just get some 7/16" chrome lug nuts for the rear. Another question that's been nagging me is why there are 7/16 lugs on this car. It is a Roadrunner (it's an RM23 car), it has 11" brakes and it does have 5 x 4.5 wheel. Curious.

Kern Dog · Aug 9, 2020

I think that you are confused or you stumbled across something completely unusual. All B body cars were supposed to have 1/2" x 20 wheel studs, the left side having LEFT hand thread until 1970 as far as I recall. I have never seen 7/16" studs on anything but an A body car.

VitaminCRR · Aug 10, 2020

I went back out to the garage just to make sure I hadn't screwed up and measured wrong and ..... nope, the old 7/16" lug nut won't fit on the 1/2" stud on the Dr. Diff rotor. I don't know what the deal is.

hunt2elk · Aug 10, 2020

I agree with KD, something doesn't add up. Are you certain a previous owner didn't swap the rear end and rotors?

VitaminCRR · Aug 10, 2020

Truthfully, I haven't looked at the rear end yet. I took the front drums off and replaced them with the disc conversion. That's when I saw the stud difference. I am only assuming the rear drums are loaded with 7/16 studs. I'll check it out today.
There are actually a lot of questions I have about this car. It has hubcaps and skinny wheels. They don't even fit over the Dr. Diff 10.95" disc calipers. The wheels rub on the caliper so I assume they are 5.5" wheels and not stock. I have ordered some Torq Thrusts for it so we'll see what happens when I can put those on. Also, it doesn't have a Sure-Grip rear end. I figured all Roadrunners came with Sure Grip. It is a numbers matching car but I think some things have been changed on it.

hunt2elk · Aug 10, 2020

That dr diff kit probably won't fit on 14 inch wheels, which is what the car would have come with new. Road Runners and Super Bees had to be ordered with a sure grip, otherwise an open rear end was standard.

Cranky · Aug 10, 2020

The road runner was the working man's car and many didn't realize what benefit the Sure Grip offered and most sales people didn't really know either. Most of the cars on the dealer's lot were ordered as cheap as possible so they weren't ordered for the 'sales bank' packed full of options. Also, young people back then were ready to jump in and go once they had the opportunity to get that car they've been waiting on for who knows how long. I didn't even know what a Sure Grip was back then lol. When you look at who were driving those cars back then, it was mostly teens and how many teens really knew cars during that time period? It did surprise me though how many Sure Grips I found in the pick and pulls in the late 70's and through the 80's and every now and then I'd find one in a land yacht....

VitaminCRR · Aug 10, 2020

Well. Turns out it was a non-issue. The rear studs are 1/2". The fronts are definitely 7/16" so maybe somebody changed the front drums during a brake job at some point. Don't know but thanks for the replies.

Kern Dog · Aug 11, 2020

Weird stuff.

RR w/11" drums and 7/16" studs

VitaminCRR

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VitaminCRR

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Kern Dog

Life is full of turns. Build your car to handle.

VitaminCRR

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hunt2elk

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VitaminCRR

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hunt2elk

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Cranky

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VitaminCRR

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Kern Dog

Life is full of turns. Build your car to handle.

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