Odd brake problem diagnosis

So, I just pulled these rotors off the Targa Miata.

Yes, they're slotted, and worn so badly that the grooves are gone. What's odd is that this is only on the inner face.

The outer face appears to have almost no visible wear. The pads show even wear on the inside and outside - in other words, the pad that tore up this rotor face looks the same as the one on the outside. The rotor wear is not reflected in pad wear. Both front brakes have almost identical wear patterns - and this is the second time I've seen this exact same problem on this car. I've not seen it on others.

Calipers are Wilwood Dynalites, a fairly popular four-piston job. They're currently on our own bracket design, although they were on Brand X for the previous set of rotors. The pads are Performance Friction PFC97. This rotor has been used for a couple of track days plus the Targa Newfoundland itself.

There are no cooling ducts to the brakes, and there's a dust shield on the inside edge with a pseudo-scoop molded in.

Ideas?

I'm definitely not an expert at diagnosing brake problems/wear but maybe the inner pistons are either dragging enough to wear it out that fast, or they are getting a lot more pressure than the outers so they are clamping alot more?
Someone back up whether this makes sense or not lol
thats a really strange one.

sounds like the calipers are not free to 'float'. Does your bracket have them bolted on without slider pins?

Heat. The higher wear side isn't kept at as good of an operating temp then the less worn side. .

jhaas wrote: sounds like the calipers are not free to 'float'. Does your bracket have them bolted on without slider pins?

or the caliper bracket is not centered correctly.

i see two pads in that pic. the one on the floor looks like it is not worn uniformly. are they both inboards?

Remove the shields, cut holes for a brake duct hose adapter and rivet one in then run a brake duct hose to the shield. Run and check for wear.

jhaas wrote: sounds like the calipers are not free to 'float'. Does your bracket have them bolted on without slider pins?

These calipers don't work the way a stock sliding caliper does.

^^^ well apparently not

Angry - those are both pads from that wheel. One inboard, one outboard. Good eye. The pad on the floor is the outboard one, and flipping the rotor over I see that there's different heat coloration on the outer 1/2" of the braking surface. The pad and rotor are worn completely evenly, though, you can only see the change. The inner pads on both wheels also show more pad material caught up in the slot down the middle of the pad - although this could be a result of the missing slots. Both discs and outboard pads have the same coloration.

The brakes have a fair number of road miles on them since they last got hot. The last day of the Targa was very wet with some reasonably long transits, so I never got the brakes up to much temp. Then it spent a day or two running around Ottawa. It's possible the discoloration on the outer faces is simply a result of light duty use - I have seen significant pad material deposition from these pads in the past on a light duty street application.

These are four-piston calipers, two pistons on each side. No float. I've seen the same wear with two different sets of CNC-machined brackets, and I've never had reports of wear like this on other cars using the same brackets. Although most others don't use these pads, nicknamed "rotoreaters" at FM due to the way they will take out a set of rotors relatively quickly when cold.

The calipers are relatively old, but with the exact same wear on each side of the car and the even pad wear I'm thinking it's not a caliper problem. The weirdest thing about this is just how consistent the wear is from side to side.

Brake ducts are in the plans - probably this weekend. My thought is that it's heat-related as well, as the only difference between the inboard and the outboard sides is that dust shield. I've been planning on developing some brake duct parts, this is just my motivation. But I'm open to any other interpretations.

Check to see if the caliper shows any distortion. When I was looking at calipers for my Camaro, I was told to use superlites instead of dynalites as the dynalights aren't as strong and can distort. Even the superlites have a warning to not going over 1200 psi at the caliper. Just something to check, especially with the wear you are getting on the front side. Check the mount as well.

I should mention that Wilwood Dynalites on a Miata are not a new idea. They've been used for at least 15 years, including in a kit from Wilwood and have been used on some very, very quick cars. Both of the mount designs I used also have a very large install base. I've never seen this wear on another Miata. However, I'll have a look at the calipers again.

That the pads show the same wear indicates to me that one side of the rotor has different properties that the other. Some sort of manufacturing process problem yielded two masses of metal that behaved very differently, and are in fact, very different masses of "iorn".

The casting cooled improperly, or the molten metal was stratified before it was poured, or there was a problem with temperature control on the pour- something like that. Someone has posted here who machines all sorts cast parts- he would know more than me.

I have indirect experience from my work with injection molded plastics- I have seen roughly the same sort of problems on plastic parts.

keith, call PFC. they love field feedback.

I had the same thing happen to my CSP 95 NA with ATE rotors. The outside was in great shape, the center of the inner side of the rotor was worn past the cooling grooves. Could never find anything hanging up, and the brakes never seemed to pull or anything.

Angry, I dropped them a line through their webform late last night. Turns out the complete tech staff is down at a racetrack called "Daytona" right now for some little event.

Keith wrote: Although most others don't use these pads, nicknamed "rotoreaters" at FM due to the way they will take out a set of rotors relatively quickly when cold.

Could this be your answer? Perhaps the inboard pad is running colder than the outboard pad?

Possibly, although with that shield in place I'd expect the opposite problem. I think it's got to be related to different heat levels on each side of the rotor.

Turns out there's a guy who just started at Performance Friction who's got a Miata with a 'Vette engine. Who knows, I just might hear back from him...

Spoke to PF. Heat. The inner face is just getting way too hot. The dust shields are already off the car, I'm going to build some proper ducting for it.