Quick please: Using under thickness front rotors on the rear.

[Heywood]

Is there any problem with using an under spec. thickness front rotor on the rear of the car? This is for the warmonger upgrade.

Sorry for the cross post but thought a lot of people might not be bothered with the long story in the other thread. Need to decide in the next hour whether to re-use or buy new ones.

 

[SVTkid]

you CAN use the old front rotors in the rear, but i wouldnt. i bought new ones and just had the alignment brackets wider in the middle at the machine shop (cost me $20). if you notice, theres little lip type protrusions on the inside of the alignment brackets, if you grind those out plus a tiny bit on each side brand new coated rotors will fit in there fine. thats probably the easiest way other than using the crappy old fronts..

 

[Big Jim]

Warmonger encouraged machining the rotors down to near minimum thickness to make the install easier (less machining of the stock brackets needed and less chance in the need of sanding off some lining or removing the shims).

Warmonger pointed out that you still end up with a much stouter rotor than the original, saying that you probably will never need to replace it.

Someone discussed machining the rotor down to the stock thickness of the original rear rotor. That would be technically illegal since it would end up being less than minimum thickness for the rotor being modified. Although that would solve problems for installation, it would open up a can of unknowns, including would there be adequate thickness before the vanes (central venting). Also, you may have a problem getting a machinist to cut a rotor under the minimum thickness specification cast into rotor for all to see. As far as I know, we never heard back from that poster as to if he found someone to cut them that thin.

 

[Heywood]

Well I got mine turned, but I never put a micrometer on them so I'm not sure how thin they are. I didn't want to bring it up at the machine shop in case they decided not to do it.

 

[Rara]

Sorry, I'm a little late to the party here, but I'll throw out some comments for anyone looking at this in the future, lol.

The minimum thickness for a rotor is decided based on a number of factors, from thermal capaicty (how much heat energy the rotor will need to handle, vs. how much material is there to handle it) to structural strength of the rotor, to the pad, rotor, and caliper stackup (if the pad and the rotor are worn down all the way will the caliper piston pop out?) Stuff like that.
In the case of the Warmonger kit, where you use the front rotor on the rear of the car, you are changing virtually all of the other design parameters. You are decreasing the required thermal capacity on the rotor (compared to when it was a front rotor), and you are already thicker than the original rear rotor, so as long as you don't get carried away, its probably fine to run the rotor thinner than min. spec in this particular case.
Something to keep in mind though, is that most shops that turn rotors won't turn beyond the min spec for liability reasons. Also keep in mind that if you need to turn the rotor now to put it on, every time you buy a new rotor you will have to have it turned down.

 

[Heywood]

Thanks Rara, that was more or less why I decided to just reuse them.
I had my caliper brackets opened up so that I can use new rotors in the future. I increased the throat of the bracket by the difference between the rear max spec and front min spec, plus shaved the ridge on the back.