speedj

2004 turbo miata. SCCA class SPM

I've been working on sorting my car over the past few races this season. Suspension; now Pretty good/neutral. Could use some more neg camber F+R. Tires; I've now got rains, intermediates and dry's. Motor: I've found the melted wires. AFR's are now acceptable. Now it's onto brakes.

Past failed brake combination was willwood bbk/dtc60 up front and sport brake/hawk blues rear. It wouldn't stop... the pedal would just get hard.

The advise I got was to install a rear proportioning valve and to get to a different pad combination; carbotecks, using a reasonably aggressive pad up front and a more moderate pad in the rear. (I believe that the thought was that the Hawk blues were locking the rears and causing the ABS to trigger; therefore the hard pedal).

The problem is, I'm still waiting on pads... made to order or something; which is great, except that I've missed last weekends test day. Worse yet, I've just received an e-mail from the Oregon SCCA: They've changed the format of the this weekends race to do away with the practice, and instead substitute a sprint race.... so no way to test...

I've been able to order alternate pads from another vendor; PFC 01 front/PFC 11 rear... not exacty what was recommended to me, but guaranteed by Friday. Still, no time to test the prop valve or even bed the brakes in. Did I mention that this will probably be a rain race?

Looking on the t-miata website, it looks like the initial setup for the prop valve is "5-6 turns". For those that have a prop valve, is that correct?

I've never run PFC's before. For those that have: is the 01 front/ 11 rear a correct combo?

I'm not particularly confident that I know how to bleed the ABS correctly once I receive the pads. Using a vacuum bleeder, do you merely cycle the key on/off a few times to get the air out (from the prop valve install) ?

Thks for your replies.

ThePass

iTrader: (3)

The biggest problem is your bias. Pads aside, the standard 1.8 size brakes are a better torque match to the 11" wilwood fronts. Your pads were further exaggerating the problem because hawk blues are super high-bite on/off switches, whereas the DTC-60 is designed to have a mode gradual bite and release.

What that translates to is that as you press the brake pedal, your rear pads bite hard before your front pads ever had a chance to get to full torque and do their job. The DTC-60 is a good high-torque pad, but you never got to experience it.

So you've got two problems here, the pad mis-match and the greater mis-balance of brake bias.

Ideally, I want to run the same pad all around on the car. This gives you the most consistent braking characteristics over the entire temperature range. Staggering pads is usually a band-aid fix to solve for incorrect bias in the braking system, but it's not ideal.

Ideally, you would address the hardware issue with one of the following:

A) Change to 11.75" hats/rotors in the front + caliper brackets to move your dynalite caliper out to that position, and add a prop valve to fine tune the balance.
note: more expensive of the two options, but most ideal - with your power you could certainly use the 11.75" brakes up front

B) Change the rears to standard 1.8 calipers - you can swap caliper only, keeping the sport bracket and rotor - the standard caliper has less piston area, thus less braking torque. Again, add prop valve for fine-tuning.
note: more affordable of the two options, and quicker fix - you could have this done before this weekend. Bonus: you wouldn't need to shave the backing plates on the PFC rear pads that are coming your way, because they fit the standard 1.8 caliper

Either option above would sort out the hardware, and I'd run the same pad on all four corners and enjoy. The PFC 11 is an updated version of the PFC 01 with only minor changes - essentially same pad characteristics, super smooth and linear application/release (best release characteristics I've experienced from any Miata track pad so far - almost zero latent friction), but PFC doesn't make the 11 for the Wilwood calipers, thus the reason you have 01s and 11s coming to you.

Just moving to pads all around that have the same bite and release characteristics is going to be a big jump forward for you. If you can get your hardware sorted out by sourcing a pair of 1.8 calipers and add a prop valve before the weekend as well, you'll be doing even better.

Neither the XP12 or the PFC 01/11 are ideal for the rain - much like tires, the best situation is to have dedicated wets. But in lieu of that, you at least want a pad with very smooth modulation, which you'll have. I have run the PFC 01 in wet conditions successfully.

Also, on the plus side for your situation, the PFC pads have no bed-in procedure to worry about. Turn 1/ Lap 1 takes care of that for you.

-Ryan

codrus

Was it kicking back at you? The ABS engaging is not subtle, you can hear the solenoids cycling on and off, and the pedal will pulse under your foot.

The 2004 has the newest of the NA/NB ABS systems. Granted, it's a 3-channel system, but it does electronic biasing and supposedly has a "prop valve" that is 1:1 (i.e., not a prop valve at all, just a prop-valve-shaped union fitting). Even if the rears lock very quickly, in normal ABS operation you should still be able to brake on the front wheels -- that's the whole point to ABS.

I have a couple of thoughts. The first is that the ABS may be confused and going into "ice mode", where it thinks the car is on ice and is not doing its usual thing. Do your brakes behave like this on every corner, or only on some?

The other thought I had is that you may have a leak in your vacuum booster, possibly in the check valve between it and the intake manifold. A lack of vacuum boost would feel like that -- hard pedal, vastly reduced effect from pushing it. If you pull the electronic control fuse for the ABS (I think it's the 10A one under the dash), does it still behave the same way, or does that fix the problem?

--Ian

speedj

ThePass-Ryan:
Thank you. I did just order new non-sport calipers from mazdamotorsports... they should be in on Friday. I will give this a shot. Also, It's nice to know the brakes don't need bedding.

Most of the races I make are early in the season, so I never really have a problem overheating the brakes. Later in the season I get too busy with my work schedule and I switch tracking my sportbike... less prep and easier to pack and travel than a racecar.

Anyway, the Miata is just a blast to drive in the rain. The sticky Hoosier H2O's are just like cheating! The car is not overpowered, but has a little extra torque to pull you off the corner, or to make up for a mistake. Easy to drive close when cornering in wheel to wheel traffic... and you can get it really sideways but still "pull it back from the grave". If I can get the brakes figured out then I could find more confidence to protect my braking zone... which is where I'm lacking presently.

Codrus: ice mode? yeah that's what it feels like. There is only one corner (entering the chicane) where I scrub off a lot of speed, and that's when I feel it. I will check for a check valve leak.
I found a diagram that shows my 20A ABS fuse underhood near the passenger firewall. This is the one that I think I need to pull to set the prop valve. Please correct me if I'm mistaken. Thanks!

aidandj

iTrader: (5)

This should be stickied. It isn't really talked about and I had no idea that standard calipers fit on sport rotors with just the brackets.

speedj

A few of these parts did arrive late Friday, just in time for the race. I had to work on the car at the track, but was able to install the wilwood prop valve and try a set of PFC 01/11's.

The rear non-sport calipers from Mazdamotorsports had not yet arrived. .. The PFC-11's were for a non-sport brake rear, but were easy to modify by cutting off the top of the tab.

When trying to adjust the prop valve (abs fuse pulled), I was unable to get the rears to lock at all (?) Which doesn't make sense to me. I was only able to get up to 30mph or so on the pit access road, but no matter how I adjusted the valve (full in or full out) the fronts would lock; not the rears. I plugged back in the abs crossed my fingers and went out for a beer.

The next day showed the brakes to work pretty good! Parker Johnstone (retired indy car driver) showed up driving a slow car very fast... he got in front of the leading group of Porsches. No one could get past the guy and make it stick! This packed us up all the way to mid-pack, which made for some really exciting driving.

Thanks for all the suggestions, I am reasonably confident about my brakes at this point and was really able to engage in some close driving this weekend.

It will be interesting to play with the different pad and caliper combinations when they arrive. I don't understand why the rears didn't lock when testing (with abs fuse pulled)... maybe I wasn't going fast enough? Maybe something else is out of whack?

ooldguy

'03 Club Sport FMII ( for sale ) - Sport brakes - ducting - Porterfield front pads - OEM rear - zero issues braking from 135 mph going into turn one at Road America over two days / 5 sessions each

aidandj

iTrader: (5)

Ohhh so that's why you've been bumping random threads all morning.

ooldguy

just sharing information