how do you know when they need to be machined and why do they need it:licka:

Some people like to turn the rotors with every brake job. Personally I only do it when deep gouges are present causing uneven pad wear or pulsation of the brake pedal during braking due to warpage.

i heard you need to do it every time you get new pads

I agree with bearcatdon. Why turn your rotors when they are evenly worn? If you experience an unusual drive before you change the pads, then have then turned.

ok thanks

how do you know when they need to be machined and why do they need it:licka:

IMHO- DON'T. A new rotor is 42.00 here in taxCanada- Cheaper in the USA. If you are going to the trouble of doing your own brakes- just slap a new rotor in.

Machining a rotor that is warped removes more metal to compensate for the warpage, leading to a more quickly warped rotor:loser: .

Make sure you torque your lug nuts to the proper setting called by the manufacturer (usually 90-100 ft lbs). I used to get warped rotors every few months and since I started doing the torque procedure for about 6 to 8 years I've never had to turn the rotors on any of my cars.

Torque wrench are expensive but you can get a cheap one at Harbour Freight for about $20 and thats a lot better that guestimating your torque setting by hand alone!