Cracked brake discs.... is that bad...
02-07-2004, 08:25 AM
#1
Cracked brake discs.... is that bad...
currently ive got 285mm hi-spec front discs with the caliper on a spacer.
all around the front discs are small cracks, and ive noticed a a couple of bigger ones that have gone through the edge of the disc to the vent bits.
cant see in pic
only 2/3 of the disc is used, is that what causes this??
was thinking of getting some RS2000 calipers and 300mm discs and bells.
all around the front discs are small cracks, and ive noticed a a couple of bigger ones that have gone through the edge of the disc to the vent bits.
cant see in pic
only 2/3 of the disc is used, is that what causes this??
was thinking of getting some RS2000 calipers and 300mm discs and bells.
02-07-2004, 08:35 AM
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i have 2 cracks on my cross-drilled disc's, this is coz the bloody MOT place didn't pick up on a seized calliper coursing the piston to stick & get that hot that it burnt the paint off the pad 
02-07-2004, 09:04 AM
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Drilled Discs often do crack as 9 times out of 10, they are just plain discs with holes drilled in them rather than being designed from the start as drilled discs.
Just buy plain ones, or grooved if you must
Neil.
Just buy plain ones, or grooved if you must
Neil.
02-07-2004, 09:53 AM
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Originally Posted by fudgeass
drilled = cooling????
grooved = stops pad glaze/brake fade??
for anyone that can confirm...
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02-07-2004, 10:22 AM
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Cracked braked discs are pretty nasty if you have a Porsche equipped with PCCB brakes.... lots of these brakes have been cracking when the owners are ragging them on trackdays. The cost for 4 replacement discs and pads ONLY is Ł23,000 
Ouch... so far all the discs have been replaced under warrenty but alot of owners are removing the discs and pads (storing them until they sell the car) and replacing them with a conventional steel set ups.
Ouch... so far all the discs have been replaced under warrenty but alot of owners are removing the discs and pads (storing them until they sell the car) and replacing them with a conventional steel set ups.
02-07-2004, 10:23 AM
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Originally Posted by Porkie
Cracked braked discs are pretty nasty if you have a Porsche equipped with PCCB brakes.... lots of these brakes have been cracking when the owners are ragging them on trackdays. The cost for 4 replacement discs and pads ONLY is Ł23,000
Ouch... so far all the discs have been replaced under warrenty but alot of owners are removing the discs and pads (storing them until they sell the car) and replacing them with a conventional steel set ups.
Ouch... so far all the discs have been replaced under warrenty but alot of owners are removing the discs and pads (storing them until they sell the car) and replacing them with a conventional steel set ups.
02-07-2004, 11:39 AM
#14
Dave,
Can't believe that Chris forgot, I told him only the other day
. It is very low, as you need to allow for expansion and contraction. Do them up too tight and one they expand they will either warp the disc and / or shear the bolts. Depending on the bolts between 10-12Nm.
Fudge,
YES
. It is all down to the meturlagy (sp?) of the discs and how drilling affects this, but in layman's terms, when the discs are cast, the "molecules" are all running in the same direction, but when you drill holes in the metal, it upsets this and causes the metal to change it's direction around the holes (which stresses the metal at these points). Hence in time, they will crack under heavy use due to the stresses the holes have given the metal (due to the constant heating and cooling causing constand contraction and expansion).
The Brembo "drilled" discs on the supercars (Porsche / Ferrari etc) are in fact a misnomer, as the discs aren't drilled at all, but cast with the holes in, hence the metal's "molecules" are all going in the same direction, so no stress cracks...
Here endeth the lesson.
Can't believe that Chris forgot, I told him only the other day
. It is very low, as you need to allow for expansion and contraction. Do them up too tight and one they expand they will either warp the disc and / or shear the bolts. Depending on the bolts between 10-12Nm.Fudge,
YES
. It is all down to the meturlagy (sp?) of the discs and how drilling affects this, but in layman's terms, when the discs are cast, the "molecules" are all running in the same direction, but when you drill holes in the metal, it upsets this and causes the metal to change it's direction around the holes (which stresses the metal at these points). Hence in time, they will crack under heavy use due to the stresses the holes have given the metal (due to the constant heating and cooling causing constand contraction and expansion).The Brembo "drilled" discs on the supercars (Porsche / Ferrari etc) are in fact a misnomer, as the discs aren't drilled at all, but cast with the holes in, hence the metal's "molecules" are all going in the same direction, so no stress cracks...
Here endeth the lesson
.
02-07-2004, 11:52 AM
#17
Dave,
Would prefer a
.
Fudge,
Depends on how bad the cracks are, hairline cracks are nothing to worry about (as long as you keep an eye on them), cracks completely through both sides of the disc and you "could" end up with the disc jamming in the caliper and causing a potentially fatal accident to you or someone else that you hit as you crash off the road in a screech of one completely locked wheel.
Would prefer a
.Fudge,
Depends on how bad the cracks are, hairline cracks are nothing to worry about (as long as you keep an eye on them), cracks completely through both sides of the disc and you "could" end up with the disc jamming in the caliper and causing a potentially fatal accident to you or someone else that you hit as you crash off the road in a screech of one completely locked wheel
.
02-07-2004, 11:56 AM
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my rear discs were drilled and they cracked across the fooking holes.
hence why ive replaced them with Grooved.
i did drive with them like it for quite a while, but that was just out of lazyness... get them changed asap.
hence why ive replaced them with Grooved.
i did drive with them like it for quite a while, but that was just out of lazyness... get them changed asap.
02-07-2004, 11:57 AM
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Originally Posted by Mike Rainbird
Dave,
Can't believe that Chris forgot, I told him only the other day. It is very low, as you need to allow for expansion and contraction. Do them up too tight and one they expand they will either warp the disc and / or shear the bolts. Depending on the bolts between 10-12Nm.
Fudge,
YES. It is all down to the meturlagy (sp?) of the discs and how drilling affects this, but in layman's terms, when the discs are cast, the "molecules" are all running in the same direction, but when you drill holes in the metal, it upsets this and causes the metal to change it's direction around the holes (which stresses the metal at these points). Hence in time, they will crack under heavy use due to the stresses the holes have given the metal (due to the constant heating and cooling causing constand contraction and expansion).
The Brembo "drilled" discs on the supercars (Porsche / Ferrari etc) are in fact a misnomer, as the discs aren't drilled at all, but cast with the holes in, hence the metal's "molecules" are all going in the same direction, so no stress cracks...
Here endeth the lesson.
Can't believe that Chris forgot, I told him only the other day
. It is very low, as you need to allow for expansion and contraction. Do them up too tight and one they expand they will either warp the disc and / or shear the bolts. Depending on the bolts between 10-12Nm.Fudge,
YES
. It is all down to the meturlagy (sp?) of the discs and how drilling affects this, but in layman's terms, when the discs are cast, the "molecules" are all running in the same direction, but when you drill holes in the metal, it upsets this and causes the metal to change it's direction around the holes (which stresses the metal at these points). Hence in time, they will crack under heavy use due to the stresses the holes have given the metal (due to the constant heating and cooling causing constand contraction and expansion).The Brembo "drilled" discs on the supercars (Porsche / Ferrari etc) are in fact a misnomer, as the discs aren't drilled at all, but cast with the holes in, hence the metal's "molecules" are all going in the same direction, so no stress cracks...
Here endeth the lesson
.
From your description above Mike I would imagine its slightly inaccurate (i.e. the reasoning is the wrong way round), machining a cast metal (i.e drilling) doesn't change the material structure although can lead to stress concentrations, expecally under expansion/contraction fatigue cycles and also anisotropic properties.
Whereas casting the holes will result in a uniform grain structure around the hole and therefore better fatigue properties
.
02-07-2004, 12:05 PM
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DONT BUY GREENSTUFF!!!!!
Get some real pads. Fuck me, get some motorfactors pads - theyre better than EBC shite.
I can thouroughly recommend Ferodo DS2500's
Neil.
Get some real pads. Fuck me, get some motorfactors pads - theyre better than EBC shite.
I can thouroughly recommend Ferodo DS2500's
Neil.
02-07-2004, 01:45 PM
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They are rubbish mate. Will just warp your discs double quick!
Do a search on here for Greenstuff and have a read...
You *MIGHT* get away with it on a lighter and less powerful car, but I wouldnt chance it!
The Ferodo's aint cheap, but they are pretty damn good
Neil.
Do a search on here for Greenstuff and have a read...
You *MIGHT* get away with it on a lighter and less powerful car, but I wouldnt chance it!
The Ferodo's aint cheap, but they are pretty damn good
Neil.
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