user 72710

Hello,

Just some thoughts... I read through most of the posts in the thread and didn't see some issues addressed.

First, is about the backing plates. All the various plates on the back of the pad are for noise suppression or heat reflection. The stock diagonally cut metal plates are the noise type, and the titanium backing plates are of the heat reflection type. The downside to all of them is the same - pedal feel. Your pedal will feel slightly softer for each such plate you stick on the back of your pad. So, in my race cars, I don't use anything behind the pads...

That said, for a street car, there's obviously some advantage to not having noisy pads. And there's a clear advantage to not melting your dust boots - you should be cleaning the seals around your pistons on a fairly regular basis if you don't have dust boots - probably a few times a year. A titanium plate should significantly help prevent melting those rubber boots.

As for the concern about keeping the heat in the pads, I can't tell you what percent, but I can tell you that the vast majority of the heat of the brake system is dissipated via the rotors. The calipers aren't meant to retain or dissipate heat. Of course they get some heat, but my guess is that keeping the heat out of the calipers won't increase the temperature of the pads significantly - they're shedding their heat to the rotor, which, hopefully, assuming you have appropriate ducting, is shedding its heat quickly to the air that's flowing through the vanes. This is especially true if you have well designed rotors and ducts.

On the ABS issue - don't get into ABS while bedding, but once you've bedded, ABS all the way It's one of the great advantages of ABS - you can get on the brakes as late and hard as possible. Certainly, all the race cars that have ABS are using it all the time. I think that's what was meant, but I got confused reading the posts, so I thought I'd post my opinion.

Finally, on the matter of ducts, any air is better than none. So while the ideal duct is "sealed" to the inner diameter of the rotor, a hose at the rear of the upright that kind of points towards the access to the hat of the rotor is better than nothing. You do want to direct the air at the center of the rotor and try to get as much as possible into that area so that the rotor's vanes can pull the air outwards. Pointing the duct at the rotor surface is significantly less effective. And the aftermarket duct kits that point the air at the caliper are practically completely missing the point. Cooling the Caliper is WAY DOWN on the list compared to getting air to the center of the rotor.

Anyway, keep up the good thread. I've used the newer Raybestos race pads and really liked them. I've also been a long time PFC fan and currently we have PFC 97 and 01 pads on the Zs.

Joel, hopefully adding some useful input.

dnguyent

iTrader: (5)

I would second Dave's opinions on this. I'm using the ST41 up front and ST43 in the rear. I had horrible judder when I tried using these pads for the first time. I had swapped them in, and drove them on the street for a day (~50 brake applications). Apparently, that was not enough street driving to scrape away the street pad from the rotors.

Luckily, I had another event a week later, and just left the ST pads in there for 5 days of commuting (~250 brake applications). I did not have any more juddering on that following track day. I always bed my pads in on the first session of the day.

So, I would recommend either using dedicated rotors, or drive on the street for a 5 days to make sure most, if not all, of the street pad material is scraped off. The Cobalt Spec VR's I had before mated well with the Axxis Ultimate street pads I had on, so 1 or 2 days of street driving was enough.

As for fitment, the ST41 and ST43 pads fit great inside the stoptech and OE calipers. I can't say the same for the Spec VR because I had to grind the backing plate 1/2 mm to get them into the Stoptech calipers.

dnguyent

iTrader: (5)

This is interesting. I agree with the bedding process of not engaging ABS. Now, what I wasn't aware is that you are engaging ABS/EBD in your hard braking zones for fast laps and racing.

I try to avoid engaging ABS because I find that our ABS system seem to pulsate too slowly. Furthermore, I can't trail off the braking smoothly when the ABS goes off. The brake pedal feels like it locks up when ABS engages, and then when I release pressure, it just lets off all of a sudden.

With that said, I often engage ABS involuntarily. Either my ABS/EBD system is too sensitive to my square tire choice, or my tires are just crappy (Pirelli Corsa). I used to be able to modulate my brakes better with street tires that had staggered fitment (rarely engaging ABS, but feeling like the car is slowing down well and smooth), but I was also a lot slower then. The other parameter that has changed is that I used to have more brake bias up front (Spec VR up front and Cobalt GT Sport at the rear). I believe the mu was 0.64 front and 0.48 rear. Going equal mu front and rear and using square tire fitment might be causing me some problems; although others haven't had this problem.

Sorry for the digression....

daveh

iTrader: (9)

Joel, what are you doing for the pad knockback on your race cars? I just had new hubs put in and it didn't do a thing for my problem. My brake pedal went to the floor after the corkscrew! I'm looking into knockback springs perhaps.

dnguyent

iTrader: (5)

Let's see...how do I explain this quasi-mathematically...

Hoosiers + fast driver = NASA track record @ Infineon Raceway + Pad knockback

There is actually equilibrium in that equation. Kidding aside, I'm disappointed that new hubs didn't do squat. Your experience just squashed any hope I had for resolving this irritating braking behavior. I take it new hubs included new bearings? Does C Ray Z still claim to not get pad knockback in his Wilwood set up and stouter than heck hubs?

C Ray Z

iTrader: (2)

I have a lot of other issues like a christmas tree of idiot lights ABS, Brake, and VDC because it is turned off. I do not get a power reduction or fade but I do not have ABS working. It has not slowed me down but it is a little cause for concern.

I know part of this is the 275's all around so the system is very confused.

But to answer the initial question knock back is not an issue still. I run 2 10's at Thunderhill.

user 72710

Hello,

We have not completely resolved the pad knockback issue yet, but we do have some thoughts on the issue, which we'll test and report back here. We'll also be doing extensive testing with and without ABS just to make sure I'm not talking out of my butt - we have an ABS switch and circuit breaker in reach of the driver so he can turn it off for testing without coming into the pits (more likely, I'm thinking, to turn it back on).

C Ray Z, dnguyent mentioned "stouter than heck hubs." What are you using for hubs? I just rebuilt the CVs (interesting process and like a real puzzle - the wheel side ***** fall out and it takes a team of folks to figure out how to get them back in, since the final parts are not disassemble-able) and was looking at the hubs, next, but my bearing contacts seem to think there's not much I can do to soup up this stock bearing - the tolerances and design don't really leave any room for improvement.

Thanks,
Joel