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Old 01-18-2005, 08:28 AM
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Looking wheel bolt pattern info

I need to redrill some GM rotors to fit a Ford 5 on 4.5" I want to make my own template with 3 holes. the 2 outer to locate to the GM 4.75" and a smaller 1/8" as the pilot for the Ford. I know the radius of the Ford is 2.25" as measured from the center of the hub, not stud to stud. Does anyone know where I could find this info for the GM? Yes, I can backwards engineer but I'd rather start with "known" info to elimate as many possible points of error.

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Old 01-18-2005, 10:05 AM
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Divide 4.75 by 2. That ='s 2.375. That's the radius.
You know there are 5 bolts so divide 360 (the number of degrees in a circle) by 5. That gives gives you 72 degrees. Your GM pattern will be on the 2.375 inch radius 72 degree's apart.
Another way to do this is to make a wooden jig. Dill a hole in a 2x6 big enough to just except the rotor hub. Drill a 7/16" hole on the 2.375 Radius and use this as a pinning hole (use an old lug stud). Drill another hole at 36 degrees on the 2.375 Radius (this will set your rotor to the space in between the old lugs) and pin it so you can drill the new hole. Drill the hole offset toward the hub 1/8". Do this in a drill press and you'll have a very repeatable setup.
Mark
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Old 01-18-2005, 10:37 AM
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Thanks Mark! I wasn't sure if the fact that the Ford Radius was 1/2 of the pattern @2.25" or a coincidence. I also thought but wasn't sure that the GM studs were 7/16". I already have a paper template that I was fooling around with yesturday. I was using those exact same #'s you gave me but it wasn't coming out right. I also have to admit that it was the end of the day at work, I was extremely tired and was rushing it. I know I made an error.

Once again, thanks for your help! Much appreciate
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Old 01-18-2005, 10:01 PM
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Why don't you just use 5 by 4.5 GM rotors instead of redrilling? I just removed a set from a mustang II.
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Old 01-19-2005, 03:32 PM
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For the price and quality of brand new rotors,there really isn't much point into re-drilling rotors. Lots of places carry them. Yogi's has a nice set,Speedway has the best price. Always use a new set of bearings and retaining nuts. New dust caps are cheap and look a lot better,too. You can probably do the whole project for about $110-125.
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Old 01-19-2005, 05:17 PM
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The rotors cost about $17. They're 11" in dia. and an inch wide. The calipers loaded are about $50 a pair. The brackets cost me $63 including shipping. I have a drill press at home, so it's no problem drilling them. Over all, inexpensive disc swap. I could go the Granada route for my 66 Mustang but the geometry is different. It's not so much a problem with stock UCA's or even if I lower the UCA's 1 inch. The problem arises when using Global West UCA's. It creates a really bad bump steer to the point where it can't be corrected and makes the vehicle dangerous to drive.

While ther may be better disc kits, this is a street car and they'll be better then my drum brakes. It may sound odd to use Global west UCA's for what I'm doing but with their better suspension geometry a better motion ratio, I'll be able to keep soft springs and mild sway bar to have a great handling, well riding vintage Mustang!
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