Drilled Rotors = Warped Rotors

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redglbx
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Re: Drilled Rotors = Warped Rotors

#16

Post by redglbx »

I drilled mine & 5 other sets back around 1978 (none have warped) for the reasons Terry lists above. In the rain I had more braking power dragging my feet before drilling ! Once I drilled them I found no problems stopping in the rain, along with much improved fade resistance and also improved ride compliance due reduced unsprung weight. I’m sure I’ll hear a lot of flack over that but I could tell a difference.

I think hole size & pattern has an effect on the results and as I remember the pattern is supposed have the holes overlap, there was/is a lot more to it than just drilling holes. On my 76 the results are well worth the effort and after 40+ years of use no warping. I will add that I believe that the brake pads have an effect on all this as well, my 76 ltd has Bendix brake pads and while not as good as my drilled disc 76 it ain’t bad in the rain and fade is minimal.

On my original standard 76 I still have the oe Honda brake pads on the front (over 50k mi) and I’m on the 2nd set of EBC pads on the rear.
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
Don R
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Re: Drilled Rotors = Warped Rotors

#17

Post by Don R »

One of my patterns has holes not overlapped and it leaves lines where the holes aren't covered. I just bought a cb750 turbo bike with two drilled rotors and the patterns do not match. I'll choose the best pattern and match another one to that.
78 GL 1000, 70 CB750 sandcast, 70 CB836 hot rod, 1124cc 750 dragbike resto project.
You don't need a weatherman to know which way the wind blows.
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Fred Camper
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Re: Drilled Rotors = Warped Rotors

#18

Post by Fred Camper »

The key to drilling is to not take off too much rotor mass. Rotors have mass to limit the temperature rise, so keeping the holes modest still looks fine but leaves the rotors almost at the same weight.
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redglbx
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Re: Drilled Rotors = Warped Rotors

#19

Post by redglbx »

The thing that drilling the disc’s does is twofold, first it increases the surface area to cool the disc with the holes and then the holes allow fresh air to pass through the disc to cool it. One of the benefits is that drilling the holes also lightens the disc’s which provides less unsprung weight which allows the suspension to work more easily, not a big amount but it does affect it.

On my 76 the holes are all the same and I’ve had comments from some at shows about them being to big, they do overlap and they cover the entire “swept” area of the pads. Like I said I did 5 sets (4 wings & 1 cb750) and as far as I know none have had an issue. Should have been done oe, which most new bikes for some time now have had the disc’s drilled from new.
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
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