Warped Brembo rotors

78jotadave

78jotadave

Hero member
Location
Palm Desert, California. (near Palm Springs)
The 280mm drilled Brembo rotors on the front I would guess are warped or ?. Recently when braking hard the front axle would move back and forward and was clearly visible and the front end feel was not to be ignored. I had some spare Brembo solid rotors so I put them on and the problem went away.
My question is can the original drilled rotors be machined to function again or are they now simply done? I think I read somewhere it was not possible to machine the cast iron disc. Do any members have experience with this issue?
 
Surface grd been done before, but you start running outta disc spec pretty quickly!

Better off lashing out on a pair of 280SS discs from Metalgear Aus. I think they perform better and you get a better choice of pads 👍
 
It can be done, but, as Hooksey has explained, it's often quite futile.

Do check if the alloy adapter rings run true, many of these are also warped, especially after being fitted to freshly powder-coated wheels... they're about as flat as a sheet of corrugated iron after that!

piet
 
They can be refaced. Am sure I read the min thickness in some tech book or other. Will try and find it.... But I bet one of the experts on here will beat me to it.
 
Min. thickness is cast into the carrier IIRC. I wouldn't bother machining, just buy new rotors from Metalgear. Big improvement
When I brought Metalgear disks for the Motodd they supplied me with the pads also which seem to perform really well.
 
motoddrob said:
Min. thickness is cast into the carrier IIRC. I wouldn't bother machining, just buy new rotors from Metalgear. Big improvement
When I brought Metalgear disks for the Motodd they supplied me with the pads also which seem to perform really well.
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Yeah, I probably will source discs closer to home either Wolfgang or Bevel Heaven. The discs I just fitted are NOS they came with the 1974 3c I bought in 1977 from a bloke in North Freo, I've been hauling them around for decades (hoarder). Most of the new SS replacement discs are a good 1 pound lighter (at least).
piranha-bro2 said:
5.8mm Min. IIRC
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Yeah got that Q, on the carriers(y)
 
In many cases "warped" discs is actually corrosion between the disc and carrier and can be fixed by cleaning up the surfaces. Worth checking before forking out for new. That info from a friend who had a disc making and grinding business, he shut up shop when a set from china, with pads, cost less than he paid for blanks. Not enough call for high end stuff to make it pay, sad story.
 
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as Piet says, Carriers also become warped and once that is done, no Rotor will run true
years ago I machined a fixture to mount the Carrier's onto a machined surface to allow me to dress the Carrier disc mounting face in the Lathe
pair I was working on were over 0.40mm out of true
 
My non-drilled rotors did the same shudder when braking hard. I stuck a dial gauge on them, and from memory, I think the run-out was around 0.3mm. There was plenty of thickness in the disks, so I sent them (with their carriers attached) away to some bloke in Queensland who was a specialist in grinding motorcycle brake disks. They came back super straight and with a nice cross-hatch pattern on the surface. Almost no measurable run-out. Braking was nice and smooth and felt like the pads had better grip on the disks.

That was about 10 years ago, and I believe that bloke has now closed up shop and retired. Shame because he did a beautiful job at a very reasonable price (about 1/4 the cost of buying new disks). There may be others around who'll re-grind motorcycle disks, but I found them to be very thin on the ground when I was looking to get mine done.
 
Might have been a clever chap called Geoff (or Jeff) who lee knew in Brissie. Another agent of expertise lost in the general demise - ageing and retiring.
 
my local machinist (sadly now died) years ago made me a "hub" from steel, a huge thing weighing half a ton, it had the "nose" (or spigot if you prefer) for the disc carriers and deep bolt threads at the right PCD, but it was huge, he used it a few times and each time he did so he mounted it in his lathe and refaced the important surfaces, (this meant the unt was sacrificial and would need replacing eventually) then he turned one side, then the other without removing it from the chuck, worked realy well every time, the minimum thicknes getting a little undercut once or twice, but we both felt there was a huge safety margin in that, and tad under 5.6mm aint gonna make no difference, I now use 320mm discs on floaters with 4 pot calipers and have never warped a disc since, plus they are MASSIVELY lighter than the cast iron stock items and this is HUGELY noticable in the steering operation.
CLEM
 
Grinding generally accepted as giving better results. The chap who did Coxy's discs has now retired. I used truedisk in the US who work with the disc on its carrier.
 
Yes, I received my disc rotors and carriers back today from Tom Tokarz @ Truedisk LLC in Michigan, my door to his and back in 8 days. Both discs and carriers resurfaced/grinding $110 ($55 each) +$36 shipping round trip, now that makes me a happy man. Check out his website, nice guy to talk/deal with. If they last only half the miles they had on them originally I will be very pleased. https://truedisk.net/
 

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I used to live on a very steep road. Neighborhood wisdom was that although brakes might overheat and fade on the descent, the warping happened when getting to the bottom and waiting at the stop sign with the brakes applied which transferred unevenly between caliper and rotor.
 
CDHE said:
I used to live on a very steep road. Neighborhood wisdom was that although brakes might overheat and fade on the descent, the warping happened when getting to the bottom and waiting at the stop sign with the brakes applied which transferred unevenly between caliper and rotor.
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This would be true. Not a common situation. In my experience most discs are knocked out of true accidentally. These days there are very few discs of sufficient thickness to actually heat warp. The modern alloy floating carrier bends easily.
The grinding process to true them is done with a toolpost grinder - which is not a common piece of kit. There was a guy local to me with the gear but like so many others, he's disappeared.
Last discs I had ground were Z1 which I wanted thinned for a racebike. A firm here first machined the bulk off then surface ground them on a machine with a magnetic table. Tedious, not cheap, but they didn't have a toolpost grinder.
 
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