Why mechanics always advise to machine the disc/rotor whenever brake pads are replaced? Won't the new brake pad surfaces eventually conform to the shape of the grooves?
Has anyone encountered problems when they did not machine the rotor/disc when replacing brake pads?
clark20,
Oct 29, 9:12pm
Just do it, yes you may get away without it but its cheap insurance anyway
The rotors do not wear uniformly across their diameter. This causes new pads to cant in their mounts and if wear is substantial you can expect to get juddering.
In some cases replacement is as cheap as machining.
robotnik,
Oct 29, 10:02pm
I've read that it isn't the rotor metal which gets scored, but rather things like brake shudder are caused by brake pad material being baked onto the rotors.
Anyway turning brakes on a lathe is likely a con. Better to get cheap new aftermarket rotors instead of trying to machine your old ones.
marte,
Oct 30, 12:04am
As far as I know, discs can warp if hot and you go thru a stream or ford or such. Well mine did.
I am not sure, but I thought they ground the discs flat again, turning uses a tip tool, they may turn and grind, or just turn/machine the discs.
Worn brake pads will wear gouges in discs, maybe glaze them too.
Discs have a minimum width, if there's enough meat left on the disc I see no reason why not to machine them. I get the impression they can be machined while still on the car too. Mine were not. They did them on a machine, I'm not 100% sure the guy knew how to machine them either. The cup wheel should have been grinding from the outside edge to the inside, taking a few skims. I got the impression he was grinding right across the face of the disc in one go, just grinding deeper. I didn't see the 'swirly' marks on the disc. Looked like there was hotspots too. That was 15 odd years ago, don't have the car anymore.
marte,
Oct 30, 12:15am
If putting new pads on a grooved disc. Yeah I would machine the disc if possible. Depending, I'd probably even use a 9 inch grinder on a different car. Just to take off the peaks. (My current car had its discs changed 10 KKm's ago or less)
jgiblin,
Oct 30, 5:08am
here is what you do,,,,
Price up new disk rotors.
Price up disk machining cost.
If the price of new rotors is more than $40 more than skimming the old discs id still put new rotors on. Your old discs by this stage of their live have done a few turns and are by now likely getting on the thin side so will need changing anyway next pad change.
bjmh,
Oct 30, 5:24am
cause I have to pay for my new on-board brake lathe. that's why
Been putting in new pads on various things for many years and not yet had a problem. I accept that if rotor is warped or scratched it's needed. BMW insist that the pads and rotor be changed together, something about harder pads softer rotor wearing together and rotor being too thin by the time pads worn. Must agree that's how it's worked with my old BMWs . pads last massive miles but when worn rotor is too thin. Which leads me to worry about this skimming business. Should there be enough metal left?
bjmh,
Oct 30, 8:38am
Which leads me to worry about this skimming business. Should there be enough metal left?
Quote
tamarillo rotors have a minimum thickness ,if they are past that. bin them and fit new rotors.
intrade,
Oct 30, 8:46am
machining of rotors is only required if there is a problem like extreem warpage, brake pads bed in without any doing . also by the time you have problems the disk is usually to thin hence it warped so machining is not going to fix that a new set of disk is the fix in this case, and if you got no abs and the brakes work then you can just ignore its warping like on my old tipo diesel it pulses qzute a bit if i have to brake hard from 100kp and that is almost never because i dont need to brake hard at high speed because i slow down befor i would require to brake hard and then there is nothing there to feel hence it always passed the wof
intrade,
Oct 30, 8:53am
now on some more fast cars with heavy duty disk it would make sense to skim for 2 reasons it could mess with stability controll junk if it pulses . and if you where to drive at 250kph like on german motorway then it could become dangerous to brake with bent discs and harsh braking . but the secound one is not likely as the speed limmit is 100kph right .
pandai,
Oct 30, 9:57am
I had warped rotors that shook the car when I used the brakes at speed. Felt like a badly balanced wheel, if the brakes were hot and I touched them, I felt it through my seat, the steering wheel, and the pedal.
When I got the pads replaced I got the rotors machined (on-car) as well. Getting the discs machined while they are on the car means they are true to hub. I would not let someone remove the discs to machine them.
All has been well since.
daryl14,
Oct 30, 10:19am
I had new pads put on my old maxima by a brake specialist and the guy did not skim the disks. After that the bloody thing had an annoying loud squeal at low speed / soft braking and the only cure that eventually worked was to sell the car.
johotech,
Oct 30, 10:48am
That guy might have pro tools, but he forgot to tighten the rotor chuck onto the machine spindle.
This. Auto outlets have stuff like this, often pads come with little pouch of it.
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