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So - pad knock back - I always do a very quick and light left foot double tap of my brakes, especially on long straights/hard braking zones. It sets the pads and also verifies I have brakes...right foot is to the floor while doing this. Give it a shot next time out. If your brakes are going this helps you keep on pace as well.
great idea TrackAire. and do you think my cam amplfies the issue? i know cams cause vacuum issues, but i always assumed it was more at idle.
just to clarify your wording "i was hard on the gas" technically i wasnt on the gas at all, i was braking/coasting, and the down shift causes the high rpm when i let the clutch out. so while the RPMs were high, i technically wasnt on the gas at all. just wanted to specify that as you may be on to something, and i thought it might help diagnose.
also the pedal isnt hard (due to what your calling lack of assist. ie like not having power brakings.) it pedal is hard because its being forced back at me by a hydrolic force.
Well damn....with your clarification I think you should have seen very a high level of vacuum when under compression braking......hmm. Your cam might be making the issue worse, but it would be interesting to see what kind of vacuum you're pulling with the cam on engine decompression. If it is really radical it might be worth looking at its ability to produce vacuum. You could always install a 12 volt vacuum pump to supplement the stock system if needed.
Ok, here are two last thoughts.....
1. You could have a mechanical issue with the brake booster/vacuum assist system.
2. If you are running an oil catch can to prevent oil from getting sucked into the intake, make sure it is hooked up correctly and not "sucking where it should be venting or vice a versa). I have seen an issue that when people routed the catch can incorrectly to the intake it was screwing up the vacuum and making the brakes less effective.
Regarding the push back you feel...I've had to drive a couple of vehicles that had total brake booster failure on the street and when having to "hit" the brakes quickly, it kind of did feel like the pedal was trying to push back without the assist. I would think that under the stress and minimal time to react on the track, it would be very hard to tell if the pedal was pushing back or just sort of bouncing back from the hydraulics not being very compressible. At this point, I'm really not sure what direction to go without being able to see brake pressure psi, vacuum readings, etc.
I have used DTC 70's on the front and DTC 60's on the rear of my track Mustang and felt it was a good combo....but never at the cooler ambient temps you were experiencing.
StangKilla, this is mostly duplicate from LS1Tech, more for the readers here.
I HIGHLY doubt he has a brake vacuum issue. I autocrossed my 01 Trans Am for years thinking I had a brake vacuum issue - I tried canisters, electric motors, different check valves. Nothing worked. What I finally realized was ICE MODE is real, and whenever I'd toss the car hard into a corner and stab the brakes, I'd get ice mode and they symptoms are exactly as described: "At high RPM, I get no brake, the pedal is hard as a rock, overshoot the corner, brake power is maybe 25% of normal". I too thought it was brake vacuum b/c of the hard pedal. But in fact the ABS unit literally closes the input lines, so you can not push more fluid. The computer takes over and reduces brake power until you slow down and get straight.
It was never on slow corners, usually fast ones - corners where you'd have higher rpm because of higher speed, and being way too aggressive on the brakes suddenly. Drive the same corner with earlier/smoother braking helps.
Given that StangKilla put new huge calipers on, and it was cold out, the tires had less grip, maybe one wheel locked up very fast (hit a little bump even) and during trail braking, the computer panicked and went ice mode.
I'd also surmise that he could rev high and go fast in a straight line and not have the described symptoms, b/c in a straight line you aren't getting wheel lock up at different rates. It would confirm brakes are fine physically.
I won't rule out maybe some other issues. But if his car is mechanically in good shape, I'd put $1000 on ice mode, and that changing driving style would alleviate that.
StangKilla, this is mostly duplicate from LS1Tech, more for the readers here.
I HIGHLY doubt he has a brake vacuum issue. I autocrossed my 01 Trans Am for years thinking I had a brake vacuum issue - I tried canisters, electric motors, different check valves. Nothing worked. What I finally realized was ICE MODE is real, and whenever I'd toss the car hard into a corner and stab the brakes, I'd get ice mode and they symptoms are exactly as described: "At high RPM, I get no brake, the pedal is hard as a rock, overshoot the corner, brake power is maybe 25% of normal". I too thought it was brake vacuum b/c of the hard pedal. But in fact the ABS unit literally closes the input lines, so you can not push more fluid. The computer takes over and reduces brake power until you slow down and get straight.
It was never on slow corners, usually fast ones - corners where you'd have higher rpm because of higher speed, and being way too aggressive on the brakes suddenly. Drive the same corner with earlier/smoother braking helps.
Given that StangKilla put new huge calipers on, and it was cold out, the tires had less grip, maybe one wheel locked up very fast (hit a little bump even) and during trail braking, the computer panicked and went ice mode.
I'd also surmise that he could rev high and go fast in a straight line and not have the described symptoms, b/c in a straight line you aren't getting wheel lock up at different rates. It would confirm brakes are fine physically.
I won't rule out maybe some other issues. But if his car is mechanically in good shape, I'd put $1000 on ice mode, and that changing driving style would alleviate that.
The first guy that comes up with a programmable way to lessen or eliminate ice mode will make some good money. There are just too many variables for the anti lock algorithm to figure out what is going one, especially once we use sticky tires, different brakes, suspension upgrades, etc. I wish I could just have a way to electronically turn it off without having to move to a Bosch system or some other uber expensive solution.
The first guy that comes up with a programmable way to lessen or eliminate ice mode will make some good money. There are just too many variables for the anti lock algorithm to figure out what is going one, especially once we use sticky tires, different brakes, suspension upgrades, etc. I wish I could just have a way to electronically turn it off without having to move to a Bosch system or some other uber expensive solution.
I hear of this DIY "BMW programmable abs" setup some people have been figuring out. The other option is the $8000 Bosch unit LOL. There is always manual brakes too.
I drove a friends C5 at a local atuocross and felt ice mode...SCREW THAT FEELING. My 95 LT1 Camaro Z28 was rock solid and predictable every single run. It's nerve-racking thinking about ice mode lol
Last edited by smitty2919; 03-06-2019 at 04:05 PM.
wheel bearings have no way of pushing the pedal back at me?
Sorry
wasn't paying enough attention to "hard pedal"
Does sound like ice mode. Much info, some conflicting, but in my C5Z experience happens with some yaw and rear wheel slippage on fast application of the brakes. Lack of enough stagger makes it more likely to occur. GM has been offering reprogramming of some recent camaro ABS controllers to a more "motorsports" friendly calibration. I don't know if Corvette is in the mix. Best bet is slower initial application of the brakes.
EDIT!!! CORRECTION
eLSD controller reflash... Not EBCM reflash
Still stuck with ice mode I guess
shaved about 9 lbs. but i really bought it for the cooling, and reducing front end lift.
few cool cars there
Mike Dusold was there with his twin turbo '67 from the Optima Street car series
also a 488 GT3 prewrap. a AMG GT3 also rolled by in the same all white, but i couldnt grab a pic fast enough
Thanks to a tip from Sam Strano i swaped my OEM rear pads back on and it fixed my braking issue! (pedal push back on downshifts) now i find myself needing a bit more braking power, but i think i can get there.
dispite the horrible grip of the Toyo R888R, ive been working on a few corners and learning the track better, and was able to set a new PB.
my previous PB was a 2:25.7, did back to back 2:24.9s! still lots to learn but happy with the improvement, especially on these terrible tires.
You seem to pick a track and stay with it. You will learn faster by doing more tracks. Similar but different corners require different approaches. The similarities can be applied to other tracks and extrapolated to improve lines on both or more tracks. Is this something you've considered that I've missed?
That's quite the setup. As we know you intend to go W2W with this car which will involve multiple tracks. Is that something you're financially prepared to do?
plans are to just stick with COTA and Cresson. at least for the first 5 years or so. thats only a few races a year.
ive sorta back burnered the w2w plans possibly, or at least there not as "right now" as i had origonally planed.. and continue to rent seats, until that becomes an issue. which sadly looks like this years COTA WRL race, the car i wanted is already booked.
went back to the track last monday.after success with the OEM rear pads fixing my braking issue, i swaped to some more agressive ST-43 pads i had laying around. they worked great as well. with more stopping power of course.pretty uneventful day of fun. still hating the R888R tires though. horrible grip. cant wait to burn threw them. got a set of Rivals waiting.
went back to the track last monday.after success with the OEM rear pads fixing my braking issue, i swaped to some more agressive ST-43 pads i had laying around. they worked great as well. with more stopping power of course.pretty uneventful day of fun. still hating the R888R tires though. horrible grip. cant wait to burn threw them. got a set of Rivals waiting.
Seems like you got the braking issue figured out. Couple things to add to it- you can call Wildwood and see if they have anti-knock back springs available for those calipers. And if you run into this again try pulling your ABS fuse and doing more laps. The braking WILL feel different, but it was a better different imo with aftermarket calipers. May need to change pad compounds after pulling the fuse as the change is that noticeable. After going to the AP calipers when racing T1, the fuse pull was my only fix for ICE mode. Had a few scary moments with it and it didn’t take much to convince me on taking it out. A few of us went back on forth on the issue. I think Oli made it work leaving it in, I left it out, I think Kyle pulled it out and Carl left it in. I agree with others and think it comes down to driving style. I typically do all my braking when I first push the pedal. I want that initial bite.
Who's ricer Corvette is that with the non-legit APR wing in the video?
lol a guy with a WELL preped/sorted car. and a lot of experience.
my track knowledge was the only thing that kept me ahead of you. i dont think the outcome will be the same next time.....
Seems like you got the braking issue figured out. Couple things to add to it- you can call Wildwood and see if they have anti-knock back springs available for those calipers. And if you run into this again try pulling your ABS fuse and doing more laps. The braking WILL feel different, but it was a better different imo with aftermarket calipers. May need to change pad compounds after pulling the fuse as the change is that noticeable. After going to the AP calipers when racing T1, the fuse pull was my only fix for ICE mode. Had a few scary moments with it and it didn’t take much to convince me on taking it out. A few of us went back on forth on the issue. I think Oli made it work leaving it in, I left it out, I think Kyle pulled it out and Carl left it in. I agree with others and think it comes down to driving style. I typically do all my braking when I first push the pedal. I want that initial bite.
thought i had heard removing ABS fuse wasnt good idea on vette. changes f/r bias ratio and some other things. doesnt just disable ABS.
lol a guy with a WELL preped/sorted car. and a lot of experience.
my track knowledge was the only thing that kept me ahead of you. i dont think the outcome will be the same next time.....
If you can fit in his passenger seat a ride along with him is a blast! Next year I'll make Cresson, seriously I keep missing out..
thought i had heard removing ABS fuse wasnt good idea on vette. changes f/r bias ratio and some other things. doesnt just disable ABS.
Changing bias is correct. After playing a little more with pad compounds though, I preferred it over a milder pad with ABS active. ICE mode actually happened to me mostly when I was testing R888s to run in a SCCA Pro class with the vette and that was the spec tire, but it did happen a couple times on Hoosiers. I made the choice to pull it and be done. Just something to think about if it happens again. Then just make the change to one pad compound more aggressive front and rear or try just front first then rear
03-05-2019, 07:35 PM
