Caliper Flex?
 

Preface: My Evo has become a track toy. I'm in NASA DE3 and will probably be running in TT hopefully at my next event. Because I am working towards entering TT, I drive the car pretty hard trying to get better.

Since moving up to NT01's I have found the following issue with my front brake pads:

https://www.evolutionm.net/forums/me...liper-flex.jpg

On the Star Specs I never had this, but on the NT01's I found the increased grip while braking to be quite a bit, so I started compressing braking zones. But I can't keep a hard pedal anymore. On fresh pads, right after seating them, the pedal is rock hard, very little travel. After the first good session, I start getting an extra 1-1.5" of travel and the pedal looses some of it's firmess. I suspect the caliper flex is causing this and the uneven wear. I know the Aluminum looses a great deal of rigidity when it gets hot.

So what is the solution? I'm running 17x9's so the BBK is not an option without new wheels. Are aftermarket calipers in stock size any more rigid (Racing Brake/Stoptech)? My current brake setup:

Girodisc 2-pc front rotors (Curved Vane)
Dba 4000 Slotted Rear Rotors
Binary Eng Brake ducts with 2" hosing
Carbotech XP12's F and R
Motul RBF600 Fluid
Technifit SS Lines
Stock Brembo's

I've had Brake fade in the past and boiled my fluid. This really feels like neither of them. Still have brakes, but pedal travel increases and they are not as firm.

As a side note, this is really screwing with my Heel-Toe, With size 14 4EEE I use the rocker method across the width of my foot and the varying height of the brake pedal under threshhold braking messes with me.

Or inside piston is sticking some on the top. Impeding an even stoke.

https://www.evolutionm.net/forums/ev...ace-stuff.html

Possible option for keeping the 17s?

Although, you may want to go up to 18s and a different wheel just to improve airflow? Seems like airflow is the only way to really avoid the issue either way as aluminum does lose a ton of stiffness with increased temepratures. Might want to try and up the tube size on the brake vents and get a good amount of the air pointed at the caliper along with the rotor.

Well, it's evenly tapered across the face of the pad and the same on both front wheels. When using a caliper spreader, they seem to move smoothly.

For s/g's how does the rotor plane look like? Square?

I think AP had some. But they are likely AL blocks as well.

Wonder if the top pad part is sliding or catching.

Rotors are pretty new Girodisc 2-pc units, very flat and square. Looks like this is not uncommon when Evo's are pushed hard:

https://www.evolutionm.net/forums/mo...ace-stuff.html

Pics from a lot of the track rats in there showing the same thing, tapered wear from caliper flex.

My street pads which have several thousand miles on them are wearing perfectly straight, but they never see the kind of stuff my track pads do. Another reason I suspect caliper flex.

Word.

Contacted AP? Maybe they can do a caliper and mount bracket that will work with the OE dia rotor? That way you can save the 2-pc.

You don't need a BBK at this level; trust me. You could, but that's $2000-4000 you don't need to spend yet. And when you get to TT; that BBK will cost you 2 pts for 'Non OEM Brake Calipers'.

I've seen some of this before too.

First off; get rid of the Motul 600. Immediately. Run the newer 660 they make or run AMSOIL DOT4 or SRF. I do the AMSOIL as several other TT and some racers do. SRF is like $90 a bottle!

I've got a 2" duct kit too; and it's really the bare minimum. Make sure it's as straight as possible and the front openings aren't covered over. And be mindful of not dragging the brake or anything.

Lastly have you ever changed out your seals? I do the fronts yearly - say 15 hard days and they're getting a bit crusty and starting stretch. If you ever pull your pads and the backs are wet, then the caliper seals are leaking already!

Nate, no fluid at all on the outside of the calipers yet. Dust boots are crusty toast, but that happened about as soon as I started tracking the car.

I need to improve the routing of the ducts, I know that. I'll get some of the Amsoil DOT4 and flush with that for the next event.

What concerns me about the pad taper, is after the pads get tapered, the pedal looses it's firmness even before I start a session and get things hot. After the pad picks up taper it only contacts the rotor on the thicker part until you press hard enough to flex the caliper and bring the whole face of the pad into contact with the rotor.

Perhaps pads with more bite would help, require less pedal pressure and reduce the chance of flexing the caliper and starting the taper wear pattern? Thinking of trying the Hawk DTC's.

Got to do something. Main problem is this varying pedal movement and inconsistent bite, really messes with being consistant on the track. Secondly, I'm wearing out a set of XP12's in the front every 10-12 DE3 sessions, which seems high.

As far as points, I'm going to enter TTS, so that doesn't matter. Down here, there is not much difference between TTS and TTA times at most tracks, and with the Evo 8 3-4 gear in the tranny (4 points) and the JDM rear bumper (?? points) as well as other mods I'd have to spend $$$ to demod-remod the car to get it competitive in TTA.

Besides, If a guy wanted to campaign an Evo in TTA, he needs to buy a certain Blue IX that is a well proven commodity :D

It is for sale...

Btw, the altered gearing is just 3pts.

If you're going TTS and don't worry about points, I'd recommend getting a different front bumper and routing some full size 3" hose short and straight. You could work up a cheap front splitter too, even homemade to start. That's all in my plans if I keep the car and goto TTS/ST2 next year. My .02

I run Hawk DTC60's and like them. There's a number of pads that'll work as 'track-only' including ST43/47, Hawk DTC60/70, some CL, PFC01's. I've ran most of them but come back to the DTC60's myself.

First and foremost; good fluid and cooling though. With the AMSOIL DOT4, I went from bleeding every weekend to bleeding like twice a year. I can even drop in new pads w/o bleeding!

I have the same thing happening in my Evo 8. Never had an issue with pad taper on street tires, but as soon as I started running R-comps (BFG R1 for me), I started to get pad taper and pad knockback. I run Castrol SRF and ghetto brake cooling ducting. I'm going to suffer with it through my next (and final) round of power mods, then I'll be saving up for the AP kit.

l8r)

Been dealing with pad taper for a while now. Running either xp10s or St43 with Motul or AMSOil barke fluid on either Z1's or RS3's.

Compared to the ST43's, which seem to have more torque with less pressure, it seems the carbos can take a tremendous amount of pressure to get all the torque out of them.

I think in my case braking too hard with the carbos caused my calipers to flex. I would try and push the pedal thru the firewall with the carbos, not so with the 43's. I have to readjust my right foot to NOT brake as hard with the ST43's. My last track day (last weekend at shenandoah) I was way over braking into turn one because I was used to needing a ton of pressure to slow the car down.

Yeah, this really started to be an issue when I went to the NT01's. Much less of an issue on the Star Specs. But the first time out on the Nittos, I was floored by how much harder I could brake without finding ABS.

Going to A6's for TT soon and this will just get worse.

But, Now I am also wondering about pads with higher mu taking less pedal effort (and therefore less caliper flex?).

Seriously thinking about the AP system......

Before spending money in an effort to solve a caliper flexing problem I would want to check if it actually exists. With the car on stands I would expect that there would be some measurable movement of the caliper at full pressure if this is happening.

Anybody used heat paint on the calipers to see how hot they actually get with various power and grip levels?

If the aluminum is getting to 300F, the metal is losing about 10% of it's stiffness and 20% of it's strength. Get it up to 400F and it's down 15-20% on stiffness and 60% of it's strength is gone. The strength is actually the bigger concern as you may actually be permanently deforming the caliper at high temperatures.

Have you measured the calipers piston faces to see if they are still parallel?

^^^^Interesting stuff

I'll measure the caliper piston faces later this week when I prep it for a track day this Sat. However, the street pads are wearing nice and flat with no taper, so I would suspect this is a combination heat/load situation only coming into play in track conditions. However, the car's days of being driven on the street are all but done.....

I wonder at what temp do the Brembo's turn almost black? Mine are somewhere between very dark brown and flat out black. I know I've turned my Ti shim plates that prismatic blue that indicated they have seen over 800 degF.

Kind of spendy, but could be used for a lot of things.

http://www.amazon.com/Genesis-Brake-...8265593&sr=8-5

^Nice find.

l8r)

great solution
 

if you never turn!:lol:

The thing is, these people are out there with the wrenches. Some of their ideas will work and some will be dead ends. I want to encourage them. Eventually, somebody may arrive at a new solution we will all want to use.

It's not a new idea, the hard part is getting it to work.

The 3" duct is not a new idea, but like BarneyB, I welcome seeing any and all ideas and thoughts on how to better implement it and make it workable. I spend more in front pads and rotors than I do tires tracking my Evo. So any ideas on better cooling the brakes (and making them last longer) is welcome.

Try some Raybestos st47's to get a hard pedal. The wear on your pads looks like rotor flex to me. Have you tried the new CL pads yet? You can burn up a set of the RC6 in one track day.

Why do you suggest rotor flex over caliper flex?

Seems like the rotor would be considerably stiffer then the caliper as you are loading the rotor in "axial" compression. The caliper on the other hand, you are inducing bending moments in the bridge. Objects are much stiffer in axial strain then bending.

2 piece rotors? Pretty big ones stock on an evo. Look were the wear is. Then read this. http://www.stoptech.com/tech_info/wp_knockback.shtml Also explains the low pedal that gets firm after a few pumps, maybe you notice it more after that long bumpy high G sweeper?

Randy Pobst was at a track day I attender a few years back at Road America and I asked him about this "knockback" thing on my evo. He told me he did a left foot tap up before every brake zone after any period of brake inactivity. Good enough for Randy and it works for me.

I do the left foot tap towards the end of any long straight (like the back straight at RA). This isn't knockback. I get some pedal resistance as soon as I push and some braking, but to get to hard (threshhold) braking I have to mash pretty hard on the pedal and it sinks as I do. Not a lot. but anough to hose my heel toe most of the time. Pumping the pedal doesn't help, been there tried that.

Looking at that pad, after that wear pattern sets in, then when the pads start to press on the rotor, the only thing touching on the outside pad is that lower edge. I suspect I am having to press hard enough to flex the caliper and bring the whole pad face into the rotor.

Driving it around after re-installing the RB ET700's and street wheels/tires, the pedal is rock hard and has almost no movement. Of course those pads are wearing nice and flat (even on both sides).

makes no sense, you have equal pressure on both sides of the rotor when you hit the brakes, unless the caliper is flexing without brake application. the uneven wear is at the outside edge of the rotor on both sides, if it were indeed the caliper flexing wouldn't you see pad wear at the center portion of the rotor on one side and the outer edge on the other pad?

put a set of rabestos st47 on her and let me know how they work.

The inner portion of the caliper is also the part bolted to the knuckle assembly, which acts as a brace on that side making it much more rigid than the outside which is solely supported by whatever material is bridging the span over the rotor. Under pressure the caliper is going to act like a C clamp that is overtorqued and try to spread. Since the inside is essentially fixed due to the mounting bolts and extra bracing from them, it leaves the outside free(er) to deflect. The most deflection will occur at the point of highest leverage (inner portion of the rotor). As you move across the face of the caliper towards the outside edge of the rotor, it becomes a much more rigid structure, and deflects less.

Hope this makes sense, might get on Cad and do a free body diagram.

makes sense, but I'm leaning toward the flex being in the rotor and the hub, I've seen wear uneven from front to rear of the pad, explain that one.

That is why there are staggered pistons sizes in calipers. Also, the pad tries to "dig in" more upfront as you basically have a center of stiffness that the pad tries to rotate around.

except..
 

...the open side of the C-Clamp is toward the inner part of the rotor.

Thus the reason there is less pressure on the inside area and the pad tapers towards the top. The top of the pad is the thinnest as it gets the most load applied to it.

Here is a crappy MSPaint diagram...

http://i874.photobucket.com/albums/a...1/PadTaper.png

The inside pad stay flat as there is much less flex on this side (hub and bearing flex would lead to inside pad taper). The outside pad gets tapered due to the bridge flexing and putting the pistons on an angle to the rotor.

That's a good MS cross section :)

Thing is though, caliper connects back at front and rear (large section too).

Jim,

Can you measure both top and bottom (as picture is) for base to top of pad material.

Question might be is the caliper flexing or rotor/hub under load.

I know I posted up earlier that I've seen this on my Evo...

But had more of it this weekend at Road America. Didn't know how hard this track was on brakes, including T5 which for me was 147mph down to 45mph and downhill! I ran 2 sets of pads that were < 50% to begin with so that's an issue there.

I think both fronts had the outside pad wear a little more at the top vs the bottom. Not a crazy amount more, but a little. I last replaced all the seals at the beginning of the track season and do it yearly (I've used more than 1 set over the course of the car's life btw). My .02

Sorry, not exactly sure what you are saying here?


Something worth possibly looking at too is pad taper front to rear. If this is caliper flex, I'd also expect to see additional wear ant the lead and trailing edges as the bridge will provide more support on the edges. This would leave the center of the pad front to rear as the thickest part of the pad. Although, if you are getting leading edge wear (pretty typical on many calipers) it may make it difficult to see any such wear pattern.

Thinking on how the caliper deforms under stresses. They are connected front and rear. For that flex to happen; it would have to also stretch the thickest parts of the caliper.

Do you go full lock on the racetrack?

Maybe we are thinking differently here, but the front to rear connection at the hub has nothing to do with the pad taper we are talking about?

Caliper flex that we are interested in would be the bridge flexing. It is definitely NOT the thickest part of the caliper?

yes, sometimes
 

and for sure getting around in the pits and on the way to the track.

While it's not ideal to have reduced turning radius, the fact is you still have 60-70% of full lock running the duct along the fender liner. This is with 9.5" wide wheels. I know if I removed the fender liner and made some small tweaks, I could get that to 90% or more. There's always tradeoffs, and a in this case (at least for me) a slight inconvenience in the paddock and streets is worth the increased cooling from the bigger ducts.

Sorry if this is dumb, but has anybody thought of cutting a 2" (or whatever size ducting you're using) in the fender well and running it through to the bumper? I don't know anything about track regulations but you could use something similar to this on the bumper to route a new inlet instead of stealing from the oil cooler. This would be the most "direct" route and more efficient.

Just a thought, they never hurt. :)

Has anyone ever put brake air inlets in their hood? Obviously not for the faint of heart..

Tough to do on the drivers side as the ACD pump takes up the space in front of the driver side wheel well.

^ that and the area over hood has negative pressure

If you are pushing that hard on the pedal I'd say you need more friction. More tire will just make it worse and modulating the brakes is certainly not easy at that level of force.

Get XP16's or DTC70/PFC01 or more.

I would carefully measure the calipers as well. They may have opened up some.

PS

Same shoe size here.....a ***** getting good shoes anywhere huh...

And we do get a bit of taper from the AP caliper as well on the STi version of that kit - but the pedal never changes. I'll have to see if it' stop to bottom or end to end. We are just getting finished w/ testing it.