Grinding the lip off rear brake disk

6 replies to this topic
  • fix

Posted September 06, 2008 - 02:17 PM


Hi the rear brake disk on my wr400 has a lip on it and the bike needs to be mot'd to go on the road,i think it will go through but technically a lip on the disk is a fail.

I couls go to an engineers and get the disk flattened but i though about just going round it with a grinder,anyone tried this before or shouldnt i be doing it?


  • brad the best

Posted September 06, 2008 - 06:31 PM


on vehicles there is a minimum thickness for a brake rotor , and yes they measure it .

you should replace your rotor , when its that thin it will heat up fast and warp .

you could get it lathed on a brake lathe , but it will cost the same as a rotor . you can grind it and buff it hopefully they wont figure it out . and hopefully it doesn't warp when you grind it .the rough surface will also eat your pads .

  • fix

Posted September 06, 2008 - 10:30 PM


Thanks for the reply

I know at some point im gonna have to buy another,but aty £60 (120 dollars) they seem alot of money for what they are,especially when disks for cars are around £15 each

I think ill grind the lip doing abit at a time so it doesnt warp,the pads are fairly low so ill replace both together at some point.

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  • WR450FGreg

Posted September 07, 2008 - 01:16 AM



I've done it before like this ......

Put the bike up on a stand, leave the disk on the bike and spin the wheel in the direction the grinder will pull it (to keep it spinning). Carefully apply the grinder to the edge and keep a close eye on the amount you are grinding off.
You might need to stop once in a while to check it, then spin the wheel again.

To do the other side of the disk simply take it off the wheel and bolt the disk on with the opposite side facing out.
(It doesn't need to be mounted perfectly, ignore the countersinking of the holes etc. Though you may need to take the caliper off on some bikes for it to spin mounted this way.)
Repeat above.

Once you are happy with the grinding on both sides mount the disk back how it is supposed to be.


  • fix

Posted September 07, 2008 - 04:02 AM


Thanks for the tip Greg

I was looking at the manual and it says the remove the rear wheel to get to the disk/caliper is this the only way to get them off?

It seems abit long whinded to me!

  • roushxteam199

Posted September 07, 2008 - 04:23 AM


its easy to pull the rotor off just mark the swingarm of where your chain adjusters are and bring them all the way in and pull the axel.

  • fix

Posted September 07, 2008 - 07:40 AM


its easy to pull the rotor off just mark the swingarm of where your chain adjusters are and bring them all the way in and pull the axel.

Sorry i dont get what you mean?

Undo the bolt pull the axle towards the bike then pull it out?


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