cib24

I need some advice. I have a 99 Type RS which comes standard with 314mm x 32mm front discs and 314mm x 20mm rear discs (RZ and Spirit R also come with this) compared to the smaller 294mm units on lower spec FD models.

At the moment I am running Dixcel FP RX-7 discs front and rear. 314mm x 32mm front and 314mm x 20mm rear. These are effectively OEM replacements with a bit extra. OEM units from Mazda are like over £500 from Japan before shipping, customs and tax.

BRAKE DISC�^FP/FS�bDIXCEL

They are advertised as an upgrade to OEM-spec replacements due to the following characteristics:

• By increasing the Carbon content of the disc by 20% compared to our standard mixture, we were able to strengthen the molecular bonds within the disc.
• Stable durability even with repeated expansion and compression by applying DIXCEL heat treatment process.
• Significant improvements in crack resistance and resistance to distortion, to accommodate to the needs of our advanced users.
• Increase in initial bite by using a softer braking surface. Outstanding compatibility with various brake pad materials.
• Reduction in noise level by reducing vibrations

I run these brakes with Project Mu HC+ pads which I have been very happy with apart from the dusting which is a bit more than I would like but much less than what the Hawk HP Plus produce. Wear is slow and I haven't had an issue with them so far.

Project Mu Co., Ltd. - BRAKE PAD - TYPE HC+

My issue is that at my last track day in November at Snetterton circuit (one of the fastest in the UK in terms of average speed, and top speed on the main straight is about 135 mph) the car was experiencing significant vibrations when braking about 75% of the time, in particular when braking from above 90 mph. Sometimes so violent that the wheel would yank left or right under braking (like fighting torque steer in a 300+ bhp FWD car).

I see it as one of three things:

1. Tired calipers - mine are original as far as I can tell (approx. 80k miles);
2. Uneven pad wear somehow (maybe because of tired calipers); and/or
3. Warped disc(s)

This was my third track day on the car with about 2,000 miles of driving on the discs and pads since installing them. I had absolutely no issues prior to this day at Snetterton. I run HEL stainless steel brake lines and Motul RBF600 which I had just flushed prior to the day at Snetterton in November.

I cannot replicate this issue on the street because I need to be braking extremely hard from a high speed and it's not so easy to find a place to do that on the street. So, for now under street driving there is no problem.

Does it make sense to try to rebuild the calipers and get new pads first or just go for an uprated front brake kit? Keeping in mind that the kit needs to fit within my 17" BBS wheels.

I don't particularly drive the car that hard as I'm still getting used to it on the track. I tend to brake early and less aggressively than others and always make sure to do a cool down lap and when I park up I leave the handbrake off.

Given I only do 3-4 track days in a year and drive about 3,000-4,000 miles I would prefer to have a setup that doesn't need to be replaced so often.

TomU

iTrader: (11)

It's probably disk pad transfer from improper bedding.

-Warped- Brake Disc and Other Myths

Tech Article: Warped Brake Discs

https://www.zeckhausen.com/catalog/i...Path=6446_6444

Normal braking should "clean" the rotors, or you can try a piece of emery cloth on a sanding block. Then rebed the pads properly

cib24

Is that a common occurrence after 2,000 miles and 3 track days? I tried to follow the bedding in procedure when the discs and pads were first installed last February.

If that is all it is though I will have lucked out.

lOOkatme

iTrader: (19)

I have noticed with my set up, 99 brakes, that you need to be on them or off, no brake early long and light as the resin from the brake pads get deposited onto the rotors and they shake. get on them and get off. This approach yielded better braking and less wobble through the peddle or resin transfer. Same thing happens on my rx8 but it has good brakes oem and the car isn't nearly as fast.

TomU

iTrader: (11)

I had the same problem with stock pads that had over 15k miles on them. The problem is the heat difference between street driving and track driving. You don't get anywhere near as hot on the street. For proper bedding, you need to replicate the operating temps. According to Stoptech, "the key to a successful bed-in is to bring the pads up to their adherent operating temperature in a controlled manner and keep them there long enough to start the pad material transfer process".

Brake Pad Bed-In

I am not familiar with your specific pads. You may need to bump up to the competition pads (even though yours look good on paper, 800c and .58 mu) to sustain repeated high temp braking without transferring material.

FWIW, I run Hawk DTC 60s front and DTC 30 rears on stock USDM calipers with no problem at stockish HP levels with 255 street tires.

lOOkatme

iTrader: (19)

when I bedded in mine I could smell the brake pads and they were smoking a little. I did some 140mph to 30mph stops pretty quickly. those were the final bed in stops. I drove around for a while on them braking lightly, then 40-60 to 20mph stops and worked up. they worked much better after the bed in.

one thing I have noticed is high coefficient friction pads work well at high speeds, but are touchy as hell at slow speeds and locking up the tire. so make sure to match the pad coefficient of friction with wheel grip and speeds the car is mainly driven at. the high grip pads when warmed up can be touchy, I noticed the lower coefficient pads on the rx8 are much easier to find the brake limit, even though the ABS on the car is ridiculously good on them.

TomU

iTrader: (11)

+1, but 140 MPH may be a little tough to achieve on the street (most tracks won't let you bed in brakes on the track). I did 80-30 and it seemed to bed in ok.

cib24

Ok, I'll definitely take this into account and try to bed them in again.

Being in and around London, UK there is absolutely no way I could bed them in by going up to 140 mph and braking to 30 mph.

I bed my in last time doing a lot of 100-110 down to 60 mph on the high way, and about 70 down to 30 on normal roads that weren't populated.

ZDan

FWIW I'm running Carbotech XP10s at the track on StopTech ST40 front calipers with 328mm rotors, which fit within my 17" TE37 and Enkei PF01 wheels. Never any braking issues at the track despite >2x the stock horsepower...

BLUE TII

iTrader: (9)

My Wilwood 355mm 6 pot kit fits under 17" TE37s as well.

No idea how they track, just pointing out one can fit quite a bit under 17" wheels.

cib24

355mm? Really? Largest I ever read on 17's when searching on another car was 342mm Alcon's. But I guess each rim is different right? I have BBS RG-R's so not sure if they would have the same clearance to fit 355mm brakes but who knows.

LargeOrangeFont

iTrader: (7)

Depends on the rim. You can fit 14 inch brakes under 17 inch wheels with the right spoke profile and offset.

gracer7-rx7

iTrader: (16)

+1 on brake pad transfer although it might not be from improper bedding.

Same thing has been happening to me and a team mate in my Spec Miata ever since I switched over to running Carbotech XP10 up front. I suspect the pads and rotors reach temps beyond the heat tolerance of XP10s during a race then smear and build up on the rotor. I'm planning on switching back to Hawk DTC60 pads or XP12s up front once the XP10s wear out. The DTC60s have higher bite and can handle higher temps

My recommendation:
Have your rotors turned / machined / cut whatever they call it and switch to brake pads that can handle higher temps. The Hawk DTC line of pads are awesome.

cib24

Thanks. How are Hawk DTC for street driving and how harsh are they in terms of dust and their ability to destroy wheels?

I have mint BBS RG-R's that I don't want to hurt if I can help it. I live in London and have one parking space so don't have the luxury that most Americans have living in a 3-5 bedroom house with a 2-3 car garage and a drive way. So, I can't store separate wheels and tires

TomU

iTrader: (11)

I don't have any problem with the DTCs on the street, but due to their cost, I change them out at the end of the season with a cheaper street pad. They do dust, as do most high friction pads. You just need to hose them down and/or use a wheel protectant

Nice FD BTW. Don't crash it

LargeOrangeFont

iTrader: (7)

You can run DTC60s on the street without a problem. In my experience the dust is not bad after getting wet, but I'd wash your wheels soon after a track day if you keep your car outside and the wheels may get wet. Even if the dust sticks, there are wheel cleaners that will take it right off. Also they are not aggressive on the rotors. I just pulled a set of rotors off I ran about 6 sets of DTC 60s through in 2 years. The rotors were not significantly worn or grooved. They were starting to develop stress cracks from heat.

The pads may not last as long as others, but they are cheap, durable, and work well. Carbotechs are double the price and don't last twice as long in my opinion.

cib24

Thanks. I tend to drive like a grandpa on the street and on the track I would say I'm only ever putting about 80% into it as I don't want to crash my car!

Anyway, I was looking at the DTC 30, 50, 60, 70 and they seem to be quite noisy and dusty. Noise I don't mind so much but dust really depends on how hard it is to take off. My wheels will be sealed with a ceramic coat following a comprehensive visit to a valet and detailing specialist but I'm still skeptical whether the dust will wipe off easily anyhow, even if the ceramic coat is protecting the paint of the wheel underneath it.

My Project Mu pads don't dust too badly (more than EBC Yellowstuff) but the dust itself isn't that easy to remove. I have had to clay bar my wheels a few times in addition to using tons of iron out to try to get all of the dust off.

TomU

iTrader: (11)

I have EBC yellows on another car and they seem quite dusty to me. Don't think DTCs are any worse, and I don't find them noisy at all (but am using Ti backing plates and ceramic brake lube). Bottom line is any aggressive pad will dust. You can try using something like this to protect your rims

Wheel Protectant, Best Wheel Cleaner | Armor All

BTW, hope you've upgraded your cooling system. I toasted an engine tracking it completely stock

LargeOrangeFont

iTrader: (7)

To set your expectations, you are not going to get a good pad that does not dust. In my experience the DTCs are quiet when bedded in properly. The dust of any pads is not bad if you wash it off after a couple days, and don't let it sit out in the rain or sprinklers. the DTCs dust a moderate amount compared to other pads I've used in the past, and the dust comes off easily.

cib24

Thanks and good to hear. I know that the better the pad the more noise and dust it makes, but there is a difference in the type of dust that a pad creates depending on the material with some being harder to take off than others and also more corrosive to wheels and surrounding body paint. Based on your feedback I think I will at least try the DTC 30 which is a bit less aggressive than the DTC 60. Carbotech XP8's seem like an interesting choice as well and I have just learned about the Porterfield R4S but they are more of a competitor to the Hawk HP Plus and my current pads.

I think I am also going to invest in refurbishing all four calipers as they are originals with c.80,000 miles of use on them.

No worries about cooling on my end. Before I ever tracked it I installed a Koyo N-Flow, new OEM AST and changed the coolant. Street driving sees about 80-ish C according to my gauge tapped into the thermostat housing, and at the track I have never had it go over 95-100 C. It's oil temps and/or brake fade that takes me off after 10-15 minutes anyhow.

There are small upgrades on the car here and there but it's designed to look as OEM as possible. Full 3-inch system with high flow cat, Apexi, Ohlins, poly bushes, Nankang NS-2Rs, and now a Greddy SMIC and water injection which I need to get it mapped for in the coming weeks ahead of track day season as the weather gets better.

TomU

iTrader: (11)

If you're considering DTC-30s all around, you may want to look at HTC-10s up front. They supposedly have more bite and same upper operating temps, but not as low as the 30s. I run HTC-60s up front which are even more aggressive than the 10s with 30s in the rear. Overall, I find this a good setup, but a little front biased (may switch to 10s in the rear). You should also change your brake fluid with a high temp brand. I use ATE-200 which is somewhat of a cost compromise, but seems to work ok. Rebuilding calipers isn't hard, but there are probably better things to spend your time on. You can usually find refurbished units that are rebuilt for you.

Are you running dual oil coolers? I highly recommend them.

cib24

Thanks Tom. I will take a look at those.

I run Motul RBF600 so can't get much better than that without going for the crazy expensive Castrol SRF stuff, and I bleed the fluid after every track day or just before my next one.

Yup, I run dual oil coolers that came standard on my RS and the entire car has always been a peach except for my current braking issue. I have even been running the stock intercooler until recently at around 0.8-0.85 bar (11.5-12.3 PSI) which is a touch higher than what my car ran on the stock ECU at 0.74 bar (10.7 PSI) for a 99-spec RS 280PS model with 99-spec twins, still sequential.

It's a bit easier to get away with this kind of stuff when most of the track days that I have done take place in 45-80 F weather, so not too hot.

For this year, the Greddy SMIC is now on the car and I also have water injection plumbed in for the smallest AEM nozzle of 250cc/min just as added redundancy to ensure things keep cool and to help me reliably run 1.0-1.1 bar (14.5-16 PSI) if I desire.

Compression was recently checked as well with a Mazda Official compression tester:

Front Rotor: 7.7, 7.6, 7.6

Rear Rotor: 8.0, 8.0, 8.0

All good and I premix about 150-200ml a tank and if I'm gentle it will return about 24-25 mpg on a highway run.

Hoping all of the good fortune remains and that the stock-ish setup (guessing I am at about 320hp) remains reliable for a couple years!

BLUE TII

iTrader: (9)

Just going to point out that the bigger you go on the brake components the less aggressive pad you are going to have to run and the longer the components will last- so the car will actually be more streetable.

This is one area where the OEMs have really been stepping it up lately.

cib24

So, took off my calipers and snapped a few shots of the pads (will try to get some of the discs and calipers tomorrow).

First, the calipers seemed good. All seals were intact and nothing looked strange from basic inspection.

Second, the discs looked good. no lip, no pitting, no scoring. The only thing I haven't checked is hub run out.

Third, the pads looked pretty even all around. So, maybe no hub run out as you would think you would notice uneven wear on the pads.

Still, I've sent the calipers off for a refurbish and for a really nice painted finish and I hope that's worth more than just the paint job.

What else could cause an issue if it's not the original calipers and pistons?

Could it just be the pad material which is semi-metallic isn't suited for street and track driving?

By the way, the pads looks pretty damn good for 3 track days and about 2,000 miles of normal driving on top of that. I must not brake hard enough.

RR, FR, FL, RL

LargeOrangeFont

iTrader: (7)

Just because you were cooking the pads on track does not mean you destroyed them. You just need better pads that can take more heat.