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STANG KILLA goes "racin" Part 2

 
Old 03-05-2019, 07:23 PM
  #141  
STANG KILLA SS
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Originally Posted by AND0 View Post
Pad knock back and random vibration that comes and goes on a car thats had some track miles?

Maybe take a closer look at wheel bearings.
wheel bearings have no way of pushing the pedal back at me?
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Old 03-05-2019, 07:35 PM
  #142  
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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.
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Old 03-05-2019, 07:39 PM
  #143  
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I think he's gotten into ice mode while braking. Discussed on LS1Tech post.
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Old 03-06-2019, 01:43 AM
  #144  
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Originally Posted by STANG KILLA SS View Post
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.
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Old 03-06-2019, 12:17 PM
  #145  
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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.
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Old 03-06-2019, 01:31 PM
  #146  
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Originally Posted by SuperMacGuy View Post
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.
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Old 03-06-2019, 04:02 PM
  #147  
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Originally Posted by TrackAire View Post
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.
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Old 03-06-2019, 06:17 PM
  #148  
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Originally Posted by STANG KILLA SS View Post
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

84506758
84506759

Last edited by AND0; 03-06-2019 at 06:59 PM.
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