Rotor Wear And Re-Slotting Questions.

[No Crust Racing]

Car is S13, running S15 280mm slotted/vented RDA rotors up front with QFM A1RM pads and TRW 600 fluid home track is Winton which is primarily right turns.

Pads were gone after 2500ks so getting some new ones and pulled rotors to get them machined.

Noted that the driver side rotor has had a harder life and in particular the inner side has really copped it. So first question, is this just due to the circuit? Wheel bearings look OK on both sides.

Other thing to note is the driver side wheel arch has the oil cooler in front of it and I slotted the inner guard so air can flow through properly, would the increased heat be an issue?

I thought about pad drag, but the car isn't pulling to one side.

Now, the next question is it possible/safe to have the slots re-grooved in the rotor, Brake shop said there's enough meet on the pad to machine them but the slots on the inner driver side would be almost gone at that point. Is it just time for new rotors?

Cheers guys

[GTSBoy]

I assume that you're using the 4 pot calipers with the S15 discs? If so, then they really should give even wear both sides of the rotor, unless they're not bolted on straight or something equally bizarre. So, the thoughts then turn to sticky pistons. Maybe the pistons on the more worn side are free to move and there's some limit on the outward movement on the other side of the caliper (ie rust spot in piston bore). Or maybe there's crud in the crossover from the inside of the caliper to the outside. Either way, I would think that you'd have two options. Either;

1. machine the discs or get new ones and throw it all back together and monitor the wear to see if it keeps happening that way, or
2. strip the cailpers down for a proper rebuild and then do 1) above.

If you do 1) and it all comes good, then you've won. If you do 2) and they still wear unevenly, then you spun the roulette wheel and lost, but at least your calipers got a rebuild!

I wouldn't be tempted to throw new rotors at it if I wasn't sure that the problem was gone. I wouldn't think it would be worth reslotting the one dodgy rotor face, but by the same token, I wouldn't want to be tracking a car with 3 good slots out of 4, especially if that one more worn face is more worn because it's doing more of the work. It's not a huge problem that's going to kill you (or at least it shouldn't be), but brakes are pretty well the most important thing on the car, and they should get as much or more attention as anything else. If it was 1 out of 4 pistons in your engine that was damaged in some way, everyone would tell you to fix it before driving it on the track again, if you get what I mean.

Lastly, heat may be an issue. Perhaps you need to cable tie on some brake ducts when you go to the track. Try to cancel out any ill effect from the oil cooler.

[No Crust Racing]

Cheers for the feedback. To answer some of your qestions/respond to your points..

- I just realised that when I put those calipers on (yes 4 pot s15 calipers also) that I did not lubricate the slides so I will do that as a first step.

- Boots look good and it's no using fluid so no leaks anywhere, I'll hold off on a rebuild unless this issue gets worse/doesn't go away.

- Do you know if a rotor can actually be re-slotted in that way? I'm assuming it just comes down to whether or not there's minimum thickness in it but the brake shop guy was reluctant to do it saying go to an engineering place instead.

- I'll be putting in some ducts to aid cooling.

[GTSBoy]

There are no slides in 4 pot calipers, which is why I asked, because if somehow you were using the old S13 calipers (assuming it's possible to do so!) then stuck slides would be an obvious culprit. In opposed piston calipers like the S15 ones, the calipers stay fixed in one spot and only the pistons are supposed to move (ignoring caliper flex, etc).

You should be able to reslot, as long as you don't get carried away. One thing to consider though, is if you really need to do this, then the disc is probably down to minimum thickness on that side already. I think with most slotted discs they make the slots about as deep as the wear limit as a helpful guide. So any manual intervention on your behalf is possibly pushing the limits of what's a good idea. It should be safe enough if you're only aiming to add a mm or so of depth, but I have no idea how deep you could go before starting to really compromise the rotor.

The way to do it would most likely be just to sit it on a mill and manually trace the old slots with the cutting tool set to the depth you need. It would be hard to set it up to trace the slot shapes (assuming they're curved like most) any other way. To be honest, I reckon you could probably do a reasonable job with a small cutting burr in a dremel if you're just looking to add a little depth. Probably a little slow and tedious, but you're not likely to overdo it, and you should be able to get a reasonably smooth result.

cheers

[No Crust Racing]

OK don't shoot me for using the wrong term slides/guides whatever But there are locating pins for the pads in 4 piston calipers, if these are catching the pad it could be dragging is all I'm suggesting. These are what I mean. I didn't do anything with those or clean them up when the new pads went in.

http://www.nissansilvia.com/forums/uploads/monthly_05_2010/post-40659-12733200885677_thumb.jpg

I'll call some local engineers and see what I can do, looks like if it happens then I won't be getting another machine out of these rotors but given I'm using a harder comp pad on a soft, street spec rotor i'll be happy to get 4-5000ks out of them.

Anyone else wanna wade in on this?

[GTSBoy]

Ah, the pins. As long as they're clean and don't have any lumps of crap stuck on them, then you're unlikely to have them causing any problem.