killerpenguin21

iTrader: (20)

i am in the middle of a very frustrating saga at this point.

for two track days now, i have suffered very bad brake shudder felt as a pulsation through the steering wheel, and it is definitely not ABS (see video below).


i bought a set of used dtc60's so that i could try the compound. the first day i ran them was on a very cold and rainy day in february in which the pads stayed quite cold. fast forward to april, and i had anothee track day...this is where the shudder started, and was very un-fun. these two days were on the same racing brake slotted rotors.

i obviously just assumed that this was bad pad deposits from the winter track day, so i swapped in a set of brand new duralast blanks before my last track figuring that would solve it...nope warm ambient temps, brakes definitely got heat in them, and still shuddered although not as bad as previously.

after last weekends track day i pulled the pads and did some measuring and this is what i found:

these 2 pads are about 2mm thinner then the other two. i was running one thick and one thin on each side (these were bought used to try the compound).



the bottom pad looked more like the top one when i put them in, and the top one had less chunked out too

i did some measuring in 6 spots on each pad (picture it sitting in the caliper, leading edge = outside edge of rotor)
-top edge
-bottom edge
-leading edge upper and lower
-trailing edge upper and lower

on 3 of 4 pads, each measurement was within 0.1mm of the same position on the other side of the pad. BUT....

on one pad the leading edge of the pad differs by right about 0.5mm top to bottom which is about 20 thousandths. quick google showed the corvette taper service limit to be down in the 2-3 thousandths range i believe.

killerpenguin21

iTrader: (20)

i should also add, that i have tried stopping from 90ish on the highway and cannot replicate this for some crazy reason.

im just going to trash these pad at this point, i have a brand new set on my work bench. also, prior to the dtc60's i ran CL rc5+ pads and never had this happen, but i completely over heated and pretty much ruined that set of pads due to no cooling.


in the end...could this be anything but the pads?

grillpt

iTrader: (24)

I think the taper and the shudder are unrelated, but maybe others will tell you differently. Pads taper on these cars unless you use the OE shim. I rotate my pads from inner to outter and side-to-side to even out the wear and extend their life. No one likes having issues at the track, its super fustrating, hopefully you'll get this solved.

meckert

iTrader: (11)

man what a mess. I am thinking you have a piston sticking. What do your calipers look like? You mentioned heat in the pads--how many track days are on the rotors and calipers for reference. If you have uneven pad where and a shudder in braking when under use--something is out of round or sticking is my conclusion. Have you thought about a caliper rebuild for both sides, its not expensive-- at least the parts aren't. and I would consider some new rotors--slotted is my preference. I know the 8-9's had some brake issues early on-- mine did --with pulsing brake peddle that most concluded was from pad deposits, new pads, and slotted rotors, solved the prob. I since reworked calipers for another reason and its not a bad weekend project.. just a thought. GL.

xtnct

iTrader: (33)

Pad taper is normal, don't worry about it.

I got to a point where I had several mm difference between the top and bottom of pad. It depends how hard you are on the brakes (that is why the upper piston is smaller than the bottom: to try and even out the pressure applied to pad but obviously not enough for evo on track when using brakes hard)

Also depends how much give you have in the rest of the suspension and how deep you trail brake. This will affect how the pad wears on each side of the disc. This got virtually eliminated when I went to coilovers with 8/9K springs.

Do a search for my username - I documented a lot of issues with stock EVO brakes on this forum.

From the pics, your pads look like they have an uneven surface. What I do on all my pads (street & track) is to sand down the shiny stuff off with 150-300 grit sand paper before each swap. Then I would follow the bed-in procedure for the pad. I never had any significant shaking issues under hard braking (I did have some slight ones when trail braking though once in a while but that should be normal). The sanding does 2 things: give you a new pad surface that you can break in properly and it removes the grooves which aids to having a smoother surface disc wear and better contact.

I would also file the leading edge of the pad a few times at about 45% or so. This prevents junk building on the leading edge of the pad (you can see that in your pics) and thus limits the initiation of building up grooves on the disc.

Anyway, from your pic, the bottom pad, it looks like it has two different areas. The shiny stuff and the not so shiny (looks rougher or less smooth as the light is not reflecting so much). I would bet that has something to do with your shudder. Think of having 2 areas, each with different friction coefficients. That would give you a shudder. Even if you plan on trashing these pads, do yourself a favor and do a learning experiment. Sand the pads down, bed them in, then go out on a track session and see if the shudder is gone.

EVOizmm

iTrader: (10)

I think you need to try and re-bed in the pads.

Read this fully, you will understand how important a proper bed-in can be.
http://www.stoptech.com/technical-su...nd-other-myths

pshooter

iTrader: (8)

My experience regarding shudder has been uneven or mixed transfer layer. I now stick to 1 pad and compound and have no more issues with shudder.

2 piece rotors will help but not eliminate taper.

ReaperX

iTrader: (5)

Have you looked at your LCA Bushings or your Outer Tie Rod Ends? I had a similar shudder felt only through the steering wheel. It also cause my pads to move around quite a bit causing them to taper a bit in the bottom of the pad. Bushings and tie rod ends where both tko'd.

killerpenguin21

iTrader: (20)

suspension is ohlins 8k/10k, i think you are right about the 2 areas. the shiudder is quite disconcerting, so im pretty sure i dont wind up getting enough heat in the pads over the course of the day which leads to more crappy deposits. although these rotors look pretty even after one track day.

yeah read that article many times. these pads were bedded to the new rotors right before the event i typical fashion, maybe i didnt do it hard enough.

this has now occurred on a set of rotors that saw 3 pad compounds, but this time was a brand new set that has only seen dtc60's...which is why its sooo frustrating

there is a very good possibility that the previous owner tapered these pads, as he was a racer and i haven't been that hard on them, so im not too quick to jump to an issue in my setup tapering them. i did a once over last week, but i will look again. my thought is tho that if it was a bad bushing in the front or something, i would be able to replicate it off the track...which i so far cant.

my calipers have 6 track days on them, the dust boots are pretty gummed up and i had the thought of a sticking caliper but i didnt want to jump to the expensive fix first. but at this point im thinking i need to just redo everything to get this **** to stop.

Jer.k

iTrader: (18)

Bleed your brakes...you probably have a air bubble in the caliper. I had this happen w/ my alcon 6 piston fronts it juddered really bad w/ tapering on both pads on 1 side(right front only) after a hard day of racing.

killerpenguin21

iTrader: (20)

yeah, im due for a bleed anyway. im really thinking about doing the RB stainless pistons and new seals now just to try and solve this

GTisRule

iTrader: (5)

I went thru a very frustrating 2 years of front end shudder under braking too. I don't know if it's 100% sorted, but my problem was from warping the front rotors. I wasn't using a correct break in procedure for the rotors, so they were 'shocking' heat too fast causing warpage. This year I added brake ducting, and the first race went great! No brake issues at all dumping cold air right on the rotor hubs.

EVOizmm

iTrader: (10)

You mean hot-spotting.

I had a problem with some new rings I recently installed. Causes some extreme shuttering. I'm fairly confident it was related to the break in.

meckert

iTrader: (11)

my calipers have 6 track days on them, the dust boots are pretty gummed up and i had the thought of a sticking caliper but i didnt want to jump to the expensive fix first. but at this point im thinking i need to just redo everything to get this **** to stop.[/QUOTE]

Xtnct shared good info above.. especially the sanding of the pads-- I do that every time I change pads and got to say it helps by knocking off the pad glaze on used and new pads and seating the pads. As for the rebuild, got my kits from www.girodisc.com I think for about 75.00 for both sides-- I didnt think it was too expensive, but thats just me and if you need just the dust boots they sell those separately. As for doing it all, yeah, I work the same way, address all associated parts and be done with it. It worked for me. GL.

killerpenguin21

iTrader: (20)

well ive tried both now. last time out i just put the pads in and went, this time i bedded since it was new rotors. same results. my RB rotors need to be turned before i use them again, but the new ones after bedding/1 day look pretty good and even.

i guess at this point ive really not proven any of my theories, and i hate continuing to throw money at it not knowing what the issue is. it would be different if i could even replicate the slightest shudder...but i cant.