Rear disc conversion question

[JJSmitches]

I am converting my new 12 bolt dif to disc brakes and was given two rotors to choose from to work with this setup...

A) Caddy rotors + drill proper bolt pattern
(Tried these but the shop screwed them up and there is no way they will work now, if you need a pair of these rotors let me know and I can give more details.)

or

B) Pontiac rotors + machine hub

I now have a pair of the Pontiac rotors and they fit over the first portion of the hub, but the inside diameter of the rotor hat isnt large enough to fit over the second step of the hub.

Can I take a dremel and increase the inside diameter of the rotor hat opening to fit over the second step?

I am sure some of you know what I am talking about, but if you are a little confused the rotor hat opening slides over the hub which has two different diameters. The outter most is slightly smaller than the inner most section. The rotor fits over this fist part and will continue to slide on till it hits the second part which is only SLIGHTLY larger, thats where it stops before it is allowed to seat all the way.

[Blue70]

Can you point out what part it is you are having problems with in one of these photos?

[JJSmitches]

Sorry I am at work and dont have a whole lot to work with, if this doesnt help I will take a picture when I get home.

[Blue70]

How much is it off?
Are they new axles?
If they are old is there crud or scale built up right there at all?
If it's only off a hair I don't see where it would hurt to remove a bit from the rotor.
I think it would be best to keep a snug fit to help center the rotor on the axle.

[JJSmitches]

EDIT...

I got home took a picture to replace my very poor drawing. I was surprised to see that the difference in diameter is far less than I had remembered.

Take a look.

Called a couple machine shops and they all want around 100 bucks to make the new rotors fit. Untill I get a real quote I am leaning toward modifying the rotors myself...they wont be any worse than the caddy hubs would have been if the guy didnt mess up the bolt pattern which you can see in the pictures.

The top rotor is the Caddy and the rotor that it is layed over is the other. Top has larger inside diameter (larger than the hub) and the bolt holes were not slotted but simply drilled to a larger size. There is no way it will stay where it needs to. The rotor its on top of has the right bolt pattern but the inside diameter is too small to fit over the second larger diameter of the hub.

[JJSmitches]

Here is a close up.

[PRO TC]

are you sure its not the very outside of the hub? i just had my 12 bolt axels turned so thay would fit inside my baer rotors. the rotors are hubcentric not sure if spelled right. thay should center themselfs on that small ridge you want to grind off.my machine shop charged me 50 bucks for the lathe work. of corse i paid cash.

pro tc

[JJSmitches]

I will double check, but I had turned the rotor backwards to see if it would fit and it still got hung up.

The caddy rotors which are also supposed to work for this conversion have a much large opening to fit over that ridge and are NOT hubcentric.

The 3 machine shops I called said it would cost 100 bucks to remove the material from the rotor.

[Joe_Rocket]

I'd have a machine shop do it for accuracy, rather than trying to use a hand tool on your own. I'd want to maintain the hubcentricity of the rotor because you don't really want it to shift slightly off circle when you tighten down the wheel lug nuts. It'd be sliding in and out of the caliper slightly as it is spinning.

Try calling some other machine shops. I had a pair of hubs cleaned, turned down to fit my rotors, my new bearing races pressed in, and my new wheel studs pressed in all for $70.

[zman1969]

best way would be have the axles turned down not opening the rotors- also does o/d of axle fit inside the the hat of the rotor ? usually that part of axle is too big also