Proper way to measure Rotors and Drums?

So how do ya measure this stuff right to get what you need.

how do you measure to tell the difference from a 3-1/4" or 4" GM drum and same for an 11" or 12" rotor?

 

I'm not sure if I understand the question exactly.

For discs, if the rotor's true, you can measure the lateral runout of the bearings with a dial caliper (dial gauge with a thin rod that goes up and down behind it) when installed on the spindle. You set the dial caliper perpendicular to the rotor and then zero it out. Spin the rotor and note full deflection. If you're trying to measure rotor thickness, you'll need a measuring caliper (looks like a c-clamp).

 

How to Use a Measuring Tape - eHow.com

 

I wanna be able to measure and tell the difference between the two drums or two rotors. Not measuring to see if they are good persay, just ID which is which.

Where do you measure from to know if its 3-1/4" or 4 " drum? same for 11" 12" rotors.

rotoras might be more simple but drums are much wider then that. Id assume it has something to do with pad surface area but........

 

Wow you win first place for ahole of the week. Thats the only problem with this site, to many biters and haters with nothing to add but smartazz comments.

 

Sorry, but if you'd been clear on what you were actually asking for then it would have been easier to help.

On a rotor, measure the diameter. On a drum, measure the depth.

 

As general info: The standard rotor is 10.5 and is equipped with an iron caliper. The high-perf (1LE) rotor is 11.7 and is equipped with a finned PBR alum caliper.

JamesC