Z31 vented discs warped?

[SleeperZ]

I have Z31 vented discs on the front of my 280, using 240 hubs and 280ZX calipers. Normally for the street I run a semi-metallic pad, but it sucks for the track. After about 3 laps, the pedal gets soft and braking ability goes down. I assume it's the fluid overheating.

 

Anyway, I dropped some Porterfield carbon kevlar racing pads in it and bled the system, and had a ball at the track. The pads insulate the heat from the calipers like nothing else, braking performance was fantastic all day long. But now, and I still have the pads in, I brake hard and the pedal vibrates, not too bad, but noticeable.

 

I suppose I've overheated the rotors and they've warped a bit on me. I will have them resurfaced. Do I need to do anything to the pads surface-wise? There is lots of material left in them, and they were expensive, so I don't want to replace them. Am I dealing with the consequences of bedding the rotors with the semi-metallics before I used the Porterfield pads? What can I do to avoid damaging the rotors again? Different pads? Or duct air to the discs? Who has had experience with this?

[Pop N Wood]

About a year ago there was a long thread about the myth of warped rotors. Someone posted a link that says the vibration is not due to warp/bent rotor but an uneven layer of brake pad material built up on the rotor. The link included detailed instruction on how to "bed" in new pads to the rotors to prevent this.

 

I don't remember what the fix was once the rotors have "warped". Certainly having them turned will get the old material off, but there may be some way to bed in the pads on top of the "warped"rotors.

 

Try a search, or maybe someone will repost the links.

 

For your brake fade, replace the brake fluid with some high temp stuff. Then try to rig some type of ducting to keep the front brakes cool.

[SleeperZ]

About a year ago there was a long thread about the myth of warped rotors. Someone posted a link that says the vibration is not due to warp/bent rotor but an uneven layer of brake pad material built up on the rotor. The link included detailed instruction on how to "bed" in new pads to the rotors to prevent this.

 

I don't remember what the fix was once the rotors have "warped". Certainly having them turned will get the old material off' date=' but there may be some way to bed in the pads on top of the "warped"rotors.

 

Try a search, or maybe someone will repost the links.

 

For your brake fade, replace the brake fluid with some high temp stuff. Then try to rig some type of ducting to keep the front brakes cool.[/quote']

 

I remember reading that, hopefully it can be searched out. As I now recall, there was some good info in it.

 

The brake fade was with street pads, and I was running freshly-bled high temperature fluid. The semi-metallics are going to conduct heat right into the calipers, where my carbon-kevlar pads are excellent insulators. I'm not running the semi-metallic crap anymore. I figured ducting the brakes can't hurt, so I will look into that.

 

Thanks for the help.

[Guest greimann]

.... I assume it's the fluid overheating.

 

.... The pads insulate the heat from the calipers like nothing else' date=' braking performance was fantastic all day long. .....[/quote']

 

I think there is a false assumption here as well. Higher temperature pad materal has a different coeffecient of friction at high temperature than regular pads. They don't give off as much gas and pad material under hot, heavy braking which usually causes a regular pad to fade. The effect is like an air hockey table. The pads just scoot over the rotor on a layer of gas and dust. Drilling, slotting, or dimpling your rotors helps vent this gas too.

 

If you have a firm pedal but no brakes, then it's the air hockey effect. If your pedal goes to the floor, then you have bubbles from boiling.

[David K]

Sleeper, if your pads are still good you can lightly run them over a belt sander or orbital sander and lose the spots that formed with the mating of the disk. Its a lot better than what i do, lol. I just take the pad, put it face down on the concrete driveway, and rub really hard a few times. It makes it nice and flat lol.

[SleeperZ]

I think there is a false assumption here as well. Higher temperature pad materal has a different coeffecient of friction at high temperature than regular pads. They don't give off as much gas and pad material under hot' date=' heavy braking which usually causes a regular pad to fade. The effect is like an air hockey table. The pads just scoot over the rotor on a layer of gas and dust. Drilling, slotting, or dimpling your rotors helps vent this gas too.

 

If you have a firm pedal but no brakes, then it's the air hockey effect. If your pedal goes to the floor, then you have bubbles from boiling.[/quote']

 

Yes, then the fluid was losing it with the semi-metallics, as the pedal got closer and closer to the floor, in addition to a significant loss in braking ability, so a bit of both. But the Porterfields performed well - firm pedal, never any loss in braking ability. That's why I'm a little disappointed my rotors are vibrating on me now.

[Nismo280zEd]

Yeah i've read a couple articles on this. Warped rotors are a myth... it is caused my uneven wear of excessive pad material sticking to the rotor. Turning the rotors will give you a fresh start... from everything i've read.. best way to "break-in" new brakes is doing... 30mph-5mph w/ normal pressure on the peddle.. DON'T come to a Complete Stop! then do a couple 35-5mph slowdowns etc. you'll start to feel where the pads are seating after a while.

Hope that helps.

ED