Let's talk Wildwood calipers for mixed street/track use on Miata

Maybe I can get Keith to chime in on this one, but glad for advice from anyone.

Vehicle in question is a 2019 Miata RF, mostly stockish.  I have a short 5 mile commute so it's my daily most of the time, and also a toy that I use for HPDE once in a while.  I also own a dedicated race car that lives on a trailer, so the RF gets used for fun track days when I don't want to deal with all the race car stuff.  I'm not trying to set track records with the thing, but I would like it to stand up to the kind of track use that a pretty experienced driver/racer would give it without having to totally change my driving style.

I got the car a few months ago with some modifications already done.  One of those mods was a Flyin Miata Little Big Brake Kit (front and rear).  That kit uses the Wildwood Powerlite 4 piston calipers, and it had the pads that come with the kit: Wildwood BP-20 in the front and BP-10 in the rear.  Pretty nice to drive on the street.  First time I took it on the track with all-season tires on it, the pads faded terribly after about three laps, even with all-season tires. 

This week I put on Continental ECS tires in stock size (300 treadwear) and upgraded the front pads to BP-40 which are marketed as track pads.  I noticed that the Powerlite pads are small, probably 30% smaller than even the stock ones.  Saturday I took it to the track again and got probably 5 laps before I started to notice some brake fade.  Around lap 7 or so the pedal went to the floor coming off a straightaway, fortunately I was able to pump enough pressure to slow the car.  It was my last session of the day so I just headed home, and noticed on the highway that I was fighting a good amount of drag.  When I got home I found both front calipers completely siezed.  I opened the bleeder screws and found the fluid to be fine; with a good amount of force I was able to unstick the pistons.  Now I need to figure out next steps.  My questions:

- Did I cook the seals inside the calipers?  Will a rebuild fix them?

- Does my use case just exceed the capacity of this small brake package?  I don't want to rebuild them only to fail again.

- Is there any hope a stock brake package would hold up with the right pads under these conditions?

- Since I already have to replace pads and rotors, a bigger brake package is up for discussion.  How much thermal capacity do I gain going to a Dynapro 4 piston or 6 piston caliper?  I'd like to stay with something that fits under stock wheels.  Anyone have experience with the various ND big brake packages available?

You didn't state what fluid you're using - are you using a good DOT4 fluid such as ATE Typ200 or better? I expect you to since you also have a race car but it doesn't hurt to ask.

As far as pad fade goes, I've heard Wilwood compounds are just so-so on track. Give GLOC brakes a call and see if they have a CAD model for the Wilwood Powerlite pads (they should) and talk to them about compounds. They'll probably suggest the R8 compound for the ND. I run R12 Front and R10 Rear with ATE Typ200 fluid with Falken RT660s for my 2020 base model WRX and had no fade at all this last track day, brake pedal was strong for every 30 minute session (3x for the day plus 1x 20 minute session at the end of the day) and car slowed how I expected it to, with ambient temps at 80F+. So it surprises me that you're getting fade on a supposed track compound in a much lighter car with much better brakes than I do. 

Your use case most definitely does not exceed the capacity of the brake package, imo. If I can run 2pot claw calipers on a heavy car on the track with minimal issues, I don't see why you'd run into issues running 4 pot calipers on a light car. Not super familiar with the Little Big Brake Kit but I imagine the rotor thickness is bigger than OEM? 

This is all anecdotal, of course, so take it with a grain of salt. 

Using fresh Motul 660 fluid, just flushed the whole system a month or two ago.  When I got home with the siezed calipers the first thing I did was pop the bleeder screws to see if the fluid was pressurized or if there was any air in the lines. It looked perfect.

I've had good luck with GLOC pads and could definitely try them, I think they make a Wildwood 7912 pad shape that fits these calipers.  The bigger issue was having the pedal go completely to the floor during the session, then have the calipers completely bind up on the way home.  I feel like something must have happened to the calipers themselves, unrelated to the pads.  I can live with a little pad fade, I can't live with outright failure of the calipers to do their job.

The Little Big Brake Kit uses stock sizes rotors but at 11" they should be more than adequate for a car this size with stock power.

I'm curious if the caliper pistons overextended on track. 

Were the calipers leaking fluid when you took them out? That would be a big indicator of cooked seals.

The Powerlite pad size is 7% smaller than the non-Brembo brakes on the ND, FYI. There's some inaccurate FUD about that from one of our competitors, which is why you should never rely on one vendor to supply good information about anyone else's products.

The smaller size of the caliper and pads (relative to Dynapro-based kits) does mean you often have to run a step more aggressive in compound as they'll heat up faster and stay hotter than the bigger stuff. I've run the LBBK on track with naturally aspirated NDs quite a bit and never had a reason for concern, so I don't think there's a fundamental problem with the spec.

If your pedal went long, that says fluid. Faded pads have no change in pedal travel, just a drop off in friction and an increase in stinkiness.

I've never heard of a set sticking after hard track use. My rear Powerlites on the V8 Miata have been hot enough that the black anodizing turned pink, and they've never siezed. So I have to think something else is going on here. What did the pads look like? Any chance the pistons could have cocked in the bore somehow? Are the anti-rattle clips in place on the calipers? Those are the little vertical spring clips that sit at each end of the pad. Running without them might? maybe? allow the pad to shift and push the calipers sideways, especially if pad depth is getting low?

Why do you need to change pads? Did they wear excessively? What happened to the rotors?

If your concern is heat, one alternative to going to a bigger rotor/pad/caliper is to pump some cold air at the brakes. Verus makes a really nice ducting kit, the same one we've used on a few of the V8 NDs. Their stuff isn't cheap but you only cry once :) Alternately, I'd love to see someone come up with a nice printed inlet in place of their fancy CF unit.

*Wilwood

I wonder if the caliper bodies warped and caused the pistons to get cockeyed in the bores.

JG Pasterjak said:

*Wilwood

I just keep picturing Wildwood calipers with Realtree graphics on them

I don't know how I've made it this far through life without noticing that there's no "d" in Wilwood.  I look at the things literally every single day.

Keith, thanks for your reply.  I'm going to respond section by section.  

"The Powerlite pad size is 7% smaller than the non-Brembo brakes on the ND, FYI. There's some inaccurate FUD about that from one of our competitors, which is why you should never rely on one vendor to supply good information about anyone else's products."

That's reassuring.  I never looked at the 7912's side by side with the stock pads, it just struck me that they were on the small side.  I may have read some BS about it from one of your competitors too, I don't recall.

"The smaller size of the caliper and pads (relative to Dynapro-based kits) does mean you often have to run a step more aggressive in compound as they'll heat up faster and stay hotter than the bigger stuff. I've run the LBBK on track with naturally aspirated NDs quite a bit and never had a reason for concern, so I don't think there's a fundamental problem with the spec."

Also good to know.  The BP-20's faded quickly, which is why I moved up to the BP-40's.  I might move the 20's to the rear, because the 10's unsurprisingly faded after a lap or two.

"If your pedal went long, that says fluid. Faded pads have no change in pedal travel, just a drop off in friction and an increase in stinkiness."

I'm aware of the difference between pad fade and fluid fade.  The brakes had been bled recently and felt good until the lap where I lost them.  And when I say lost them, I don't mean they got a little spongy.  The pedal went all the way to the floor, the 2nd pump got a little engagement, the 3nd pump slowed the car.  I stayed out of the gravel trap but not by much.  After that the pedal firmed up again with a few pumps.  When I did a quick bleed at home, no bubbles came out.

"I've never heard of a set sticking after hard track use. My rear Powerlites on the V8 Miata have been hot enough that the black anodizing turned pink, and they've never siezed. So I have to think something else is going on here. What did the pads look like? Any chance the pistons could have cocked in the bore somehow? Are the anti-rattle clips in place on the calipers? Those are the little vertical spring clips that sit at each end of the pad. Running without them might? maybe? allow the pad to shift and push the calipers sideways, especially if pad depth is getting low?  Why do you need to change pads? Did they wear excessively? What happened to the rotors?"

Now we may be getting somewhere.  The calipers did turn pink from the heat.  Quick visual check after the session didn't show anything unusual.  The pads were brand new at the beginning of the day, and they were slightly worn after the last session.  Brake fluid in the reservoir was near full and clear.  I am unaware of the anti-rattle clips you describe... I've never seen or noticed them, I need to check to see if they're missing. I have noticed that when I'm driving on the street, the brakes make a "click" sound when I first hit the pedal.  Maybe it's the pads shifting, which could in theory put a side load on the pistons and cause them to bind or leak?  Driving 70 miles home with frozen calipers pretty much killed the pads, and the rotors may have a bit of life left but not much.  The engine was struggling quite a bit to keep me going 70mph.

So in summary, it's sounds like the answer is that the brake package should be fine for the job I'm asking it to do, and something else is going on.  I'm going to check on those clips, and maybe call Wil (no "d") wood to see if I can get a rebuild kit just to be sure it's not the seals.

The anti-rattle clips are visible on both the calipers in this picture - they're the vertical shiny bits in the "well" for the pads.

If the calipers turned pink, that means they're running the black anodizing (in the background of this picture). That's been depreciated for a while, I'm guessing those calipers you have must have been put on when the car was brand new as they went to the fade-free grey anodizing starting in 2018. So checking them out may not be the worst idea. If you tell me the PO's name (email keith@flyinmiata.com) I'll check to see when we shipped them.

They may have gone pink from the drive home, dragging the pads hard enough that you were struggling to hit 70.

That long pedal may have been the piston siezing, then you had to take up that volume before you could apply pressure. Maybe? Haven't come across this failure mode before. Did it happen on both sides?

Have you ever adjusted the brake pedal free play? I'm wondering if it's insufficient and your brake fluid is heating up and has nowhere to expand. That will cause the brakes to start to self-apply. I'm not 100% sure it's adjustable in an ND, I'll have to check.

BTW, Wilwood was started by Bill Wood. Why isn't it Willwood? You'll have to ask him.

For what it 's worth I've found Wilwood's tech support folks to be knowledgeable and helpful whenever I've needed support.  Even when my question was related to used parts I bought off eBay.

Confirmed that I have no anti-rattle clips. Will try to find some, although I'm having a hard time understanding how they could have contributed to my issue. Better safe than sorry I guess. 

In reply to ShinnyGroove (Forum Supporter) :

Those clips are what the pads are supposed to force against under braking forces. They hold the pads in place.  It is possible that without those, the pads are retained in place just by the retainer pins.  In that case, maybe the piston was getting tugged sideways by the pad and getting cockeyed or the seal pushing out and wedging between the piston and bore or something.

It SHOULD be a close tolerance fit but steel and aluminum are rather springy, especially with 1000psi or so of fluid pressure on the piston.