The WSM reads that brake discs are directional. Why is that? Doing a brake job now and see that my brake discs are identical, so adhering to the WSM might be difficult unless I want to purchase new. Further, are the scores wear indicators?

 

If the rotor surfaces are absolutely flat with no machined slots, they are interchangable left to right; however, the OEM '80 rotors had gas release slots machined in the braking surfaces. They are not radial, but swept back at ~30 degrees from radial. As such, they are assymetric - having a left and a right. Correctly installed, the center start of the slot defines the leading edge, sweeping back to the outer circumference for forward rotation. ( that will test anyones comprehension ). Sorry if that's not clear - I'll work on it

 

Look in between the two braking surfaces. There are fins down inside the rotors. The fins should scoop air into itself helping cooling. I think that's what they mean for directional rotors.

 

Good call - that is correct for OEM front rotors from MY '82 on: however, Rez's car is a '80 - a single rotor was offered for front axles from '78-'81, as seems to be true for all '79 - '95 rear axles.
The exception for front rotors on '80 were the gas slotted ones - which may still be available ?? ( I have a set on my '80).

 

I am a bit concerned on the fin direction issue. I think it may be that the fins are angled back in the rotation of movement forward, so as to draw air in from the center OUT.

?

 

Go check out a new Mercedes AMG - three in a row had the same rotor on each side - fins going one way on one side of the car, opposite on the other. So either Mercedes:
A. discovered some magic way to make this work
B. Can't figure out the correct way to instal them either
C. too damn lazy to install specific rotors on each side.

It's been explained to me the vents are to be installed so the force of the spinning disk forces hot air out from center NOT trying to draw in cool air (yes correct me if I'm wrong please) I know by looking at them what is correct, not 100% sure how to explain it.

 

the rotors are actually a type of radial blower. the air enters the air at the hub on the inside, and the radial veins equiped with mini air foils, route the air out the rotor outside diameter. If you look at the radial veins, you can rotate the direction of the rotor for the side it will go on, and figure out what side is left or right.
mk

 

Mark,
Thanks! that made a bit more sense than my post. A friend of mine showed me this a while ago, whenever we are at Road America, it amazes him how many track cars have the rotors on backwards.

 

Thanks for all the insight. Whent to a local auto. shop. They turned em' but the guy said it was below specs before he started.

Add rotors to the list.

 

My original rotors were worn beyond machining too. Rebuild your calipers while you have it apart. About $13.00 each for the rebuild kits. If your hoses are hard, brittle or beginning to crack, replace them too. I used the braided hoses this time around.

 

I was under the impression that air was sucked in from the center and expelled at the edge of the rotors. I guess this is something I am going to have to check via the part numbers.