Hey Guys, I am converting rear drum brakes on my factory Z car and am looking at the nice drilled/slotted rotors I got from Matts. The rotors are box labled Right and Left and when I put them on, I notice the forward rotation of the rotors9 car moving forward) the drilled holes and slots are basically sweeping from the outside in to the center, like a back wards pinwheel. This makes me feel like any derbis picked up , is swept towards the center of the hub.

Sweeping from the inside out sounds better to me. So, Which way is correct ?
If I swap sides and disregard the box stamping, then the rotation sweep look better to me.

Some one posted a wheel topic in Wheels and I notice some of these drilled/slotted rotors are sweeping front the inside out. Which way is correct? Do I need to contact Matts?

Good question, Don.

I don't know if all are the same but here's what DBA says:

http://www.dba.com.au/2006/QnA/DBA_QnA_22.asp

And here's stoptech. Interesting statement on how the cooling vanes dictate orientation.

http://www.stoptech.com/tech_info/faqs.shtml#16

Good question, Don.

I don't know if all are the same but here's what DBA says:

http://www.dba.com.au/2006/QnA/DBA_QnA_22.asp

And here's stoptech. Interesting statement on how the cooling vanes dictate orientation.

http://www.stoptech.com/tech_info/faqs.shtml#16

Thanks Rick, the Stoptech article does explain the science behind drilled/slotted rotors but goes a step further to illustrate how the internal finned rotor works, if your rotor has it. The internal centrifical air fan between the rotor faces , does indeed have some science to it and if you have these more expensive rotors, you better pay attention to their installation instructions.

Unfortunately I did not notice this when I just purchased the lesser expensive drilled slotted rotors for my run of the mill conversion.. There are the run of the mill vaned rotors (with no directional vanes ) that just have the appearance of what the big boys have .
Goes along with , you get what you pay for but then, do you actually need these high dollar items? Cruise/ Street applications, I don't. So I learned something here. Not all drilled /slotted rotors are created equal.

I did get a confession from the tech line of the maker of my rotor, he finally said I could install these rotors in any direction.
Thanks for your input. Hope this helped others too.

I've got those and mounted them with the holes on the outside hitting the pad first on rotation. Seems I read somewhere that is how non-directional vane rotors are supposed to be mounted if they are drilled so as to direct the heat towards the high-temp hub instead of at the tire bead.

Finally got back to trying to complete this rear drum to disc conversion with a kit Rightstuff kit from Matts.

Disc rotor pilot hole is about .030 too small, will not fully fit over raised lip on axle flange hub. I see comments in the instructions that if this happens, for a few dollars more I can send them back and have the pilot hole re-machined, ie. more delay and shipping costs including the labor.

Question is, has anyone taken a small grinder to the inside of this disc brake pilot hole? This appears to be cast material but coated.

I don't think anyone near me other than a major machine shop could do this.

Thanks

A lot of people take the rear axles and machine the flange hub down to fit the rotor. When I installed my rear discs I took a die grinder with a coarse wheel and went around the inside of the rotor until it fit. It didn't take much grinding. I took multiple loops around with light cutting and don't believe that the rotor's concentricity was compromised.

A lot of people take the rear axles and machine the flange hub down to fit the rotor. When I installed my rear discs I took a die grinder with a coarse wheel and went around the inside of the rotor until it fit. It didn't take much grinding. I took multiple loops around with light cutting and don't believe that the rotor's concentricity was compromised.

Thanks Andrew, guess we think alike. It was basically the 45° cut in the inside of the rotor that was not long or wide enough to fit to the edge of the small raised lip on the axle hub. I decided the neighbors had slept enough and got my hi speed die grinder out .
I was mainly concerned with a flush fit on the flange face , I put a few dabs of antiseize on the flange and reinstalled. It mated up flat so can't get any better.

I am in the process of shimming the caliper with the center of the rotor, don't know what kind of clearance is needed but I would suspect with the axle floating on C clips, you have to have some movement.

Now I have come into another snag that will kill the complete installation, Seems on of the calipers has a burr inside the threaded hole where the banjo bolts go, I started threads by finger, then used small wrench, bolt became tigher in body but brake hoses still loose. I removed the bolt and it appears to have gall marks on thread as well as banjo bolt threads. Tried to call RighStuff, you guessed it, closed. Guess I will have to contact them on the need for another caliper and bolt. Will try Matts, seems he was the middle man here. thanks

Thanks Andrew, guess we think alike. It was basically the 45° cut in the inside of the rotor that was not long or wide enough to fit to the edge of the small raised lip on the axle hub. I decided the neighbors had slept enough and got my hi speed die grinder out .
I was mainly concerned with a flush fit on the flange face , I put a few dabs of antiseize on the flange and reinstalled. It mated up flat so can't get any better.

I am in the process of shimming the caliper with the center of the rotor, don't know what kind of clearance is needed but I would suspect with the axle floating on C clips, you have to have some movement.

Now I have come into another snag that will kill the complete installation, Seems on of the calipers has a burr inside the threaded hole where the banjo bolts go, I started threads by finger, then used small wrench, bolt became tigher in body but brake hoses still loose. I removed the bolt and it appears to have gall marks on thread as well as banjo bolt threads. Tried to call RighStuff, you guessed it, closed. Guess I will have to contact them on the need for another caliper and bolt. Will try Matts, seems he was the middle man here. thanks

It's a little too late for this, but I talked to Matt about that the other day. He said it's better to have a machine shop turn the axle down a little then the rotor to keep from weakening the rotor. Also, once you grind them it takes off the zinc washing and when they start to show corrosion it'll work its way under the edge. Heck, my buddy had a good idea. He said reinstall the axle and let the car idle in gear while holding a grinding stone or something on the axle hub. I'm just dumb enough to try it if it wasn't a brand new rear that needs to be broken in right. Besides, I'm missing a part anyway.

I know what it's like to just want to get it done though. Just looking at mine, I figured they woldn't fit and to try I was going to have to drill out the stud holes since I've got 1/2" wheel studs. It was a weekend so I couldn't get anyone on the phone to see if they had a solution for maybe returning the rotors. Well, after measuring and measuring, I finally said "Screw it. I'm going to ruin one." and drilled it out to find out for sure.

I'm hitting the machine shop on Tuesday with the axles. It's not like I can finish anyway....I had to return the bracket kit and pay $75 to get the Moser bracket kit. Well, I just sent back the whole box the brackets came in since I figured it was a complete kit. Uh uh. Just brackets and bracket spacer and I needed the flange spacer from the original kit.

Thanks for the input, basically there was a 45° bevel cut on the inside of this rotor, it was only about .050 wide, sorta like a valve seat face. Well it needed to be a little wider , so I basically touched the inside edge all the way around. Rotor did seat against it and axle flange. I just thought I could same some time today, but the not deep enough threaded hole in the caliper , for the banjo bolt, shut me down. Right, can't contact Matt. Bummer.

It's a little too late for this, but I talked to Matt about that the other day. He said it's better to have a machine shop turn the axle down a little then the rotor to keep from weakening the rotor. Also, once you grind them it takes off the zinc washing and when they start to show corrosion it'll work its way under the edge. Heck, my buddy had a good idea. He said reinstall the axle and let the car idle in gear while holding a grinding stone or something on the axle hub.

My rotors have been on for nearly 3 years and there is no rust yet. The car rarely gets wet, only when washed, and I doubt the inside of the rotor gets wet even then.
I really doubt you could remove enough metal with a grinding stone, you would be at it all day long.

I really doubt you could remove enough metal with a grinding stone, you would be at it all day long.


You have never seen the flair I have for destroying things.

You have never seen the flair I have for destroying things.

Maybe with enough zeal.....