madwolf

I don't remember braking hard with my LT1 brakes (maybe because it didn't matter because they wouldn't stop anyway? :blah: ) but when I brake HARD with the LS1 brakes I have right now, they will sometimes "clunk" and feel as if they didn't brake for a moment then brake again. You can feel some movement in the pedal when this happens. Low trac light comes on too.

So what exactly is happening?

Z95m6

I believe thats the ABS kicking in. Its letting up on the brakes to keep them from locking. Its not super noticable on my car. My dads chevy truck you could slam on them and the ABS system was really loud and the pedal would move like crazy.

rlax31

I've noticed I can feel some more vibration through the pedal with the LS1 brakes, which I think is because of one of these reasons:
- the SS lines make me feel the ABS more
- When the LT1 brakes were on my ABS INOP light was on due to dirty wheel sensors, so now that the ABS is operating normally, I can feel it
- The rear brake rotors are torn up, and need to be replaced soon

Other then that mine brake damn good, and good thing too, i needed them a couple weeks ago in the rain, thank the lord I did the upgrade

Z95m6

LOL i remember that. When i had my LT1 brakes i would slam on them and the car would just gradually slow down and come to a stop. With the LS1 setup you slam on them and the car nose dives hard and it throws you forward pretty good. I love my LS1's.

madwolf

It makes sense that it's something ABS related, but I was under the impression that ABS locks and unlocks repeatedly and steadily not once and hard? Either way, my BMW does the exact same thing so I'm not worried, just curious.

The LS1 brakes are like day and night from what I had before.

madwolf

Mine nose dives the same way! I think my rear brakes are junk that's why it does it so noticeable. If they were working, I would think it would be more of a balanced braking.

But for the $190 I paid for my brakes, I'll say it's one of the best mods I did on the car. Of course, I ended up replacing all 4 balljoints, sway bar endlinks and all shocks/springs in the process so it cost me more than that, but the car feels GREAT now!

LT4Firehawk

The car nose dives because of several things (and the rear brakes aren't one of them):
spring rate
shocks
weight distribution

With a stiff enough front spring and more rebound on the rear shocks, you could eliminate much of the nose dive in an f-body. However, you probably woulnd't want to drive it on the street. Also, the very design of the car (long wheelbase, center of gravity, suspension travel), lead to built in nose dive.

As to your "clunking" issue, I've never experienced that since upgrading to LS1 front brakes either on the street or at the track. I do get an occassional "clunk" when I come to a stop, but it is from the rear. It could be ABS related as I was running Nitto 555RIIs as a street tire (just switched to KDWs), but I'd double check that all the bolts are tightened down good, and that the pads are properly seated just to make sure.

Fast Caddie

Yea the LS1 brakes are pretty good for a stock system. I have to say it's about the best money spent on my car so far. The way an ABS system works is that is "vibrates" the line pressures very rapidly, so the disk can still turn, but slow rotation only at a rate that keeps lock up imminent, using the coefficient of kinetic friction rather than static friction (lock up) so that wheel slip can be controlled. It will feel a little mushy, but the ABS is doing its job. I can hit the brakes hard at 70mph in my car and the front brakes will lock up momentarily before the ABS kicks in and unlocks them. It's unreal..... i'll have my seatbelt on and my *** will be completely off the seat the entire time until i come to a stop. Even get a slightly dizzy feeling. Very cool.

madwolf

I think my ABS acts that way because I have crappy tires and they don't grip at all. Same thing happens on my BMW.
I'll go with some Nitto RIIs in spring and I bet that will change.
Thanks guys.

PS. I did the install myself and everything was done to spec. I checked all bolts with a torque wrench and the brakes are very low mileage.

LT4Firehawk

You'll love the RIIs. I'm wishing right now that I had just gone with them again, especially since I'm getting ready to buy a daily driver so the Hawk won't be used except on nice days.

madwolf

Evan,
one last question, I promise.
What do you think of 275 RII tires on a C5 17" 8.5" wheel? I have them right now and they seem to stick out a bit (I'm reffering to rim width not stick out of the fender), but I will sell the wheels and go with something different if this will cause issues.

How about if I went with an 11" rim? (to have room for 315s if I decide to switch to those later on)

LT4Firehawk

Should be fine, especially the 555R/RIIs as they are a little narrower than other brands. Normally, the minimum width for a 275/40R17 is 9", but you should be able to get away with a .5" narrower on any brand tire, and especially on the Nittos. The only thing you might notice is a little bit slower steering response, and you'll probably need to run them at a slightly higer pressure than normal (maybe around 35psi).

madwolf

As for nose diving, I've seen it happen on Maranellos too and it seemed about the same as on my car. How does nose dive affect road racing track times anyway?

Norm Peterson

Lots of nose dive can drive your front wheels into excessive negative camber, especially if you've dialed in extra negative static camber to improve lateral grip. Read this as giving up a bit of straight-line braking grip and picking up somewhat increased wear rates for the inside shoulders of the front tires as compared to front tires that remain at closer to zero camber under braking.

Incidentally, ABS keeps track of individual wheel rpm's and releases pressure to any wheel whose rpm is slowing down more rapidly than the others or has stopped rotating completely (to mention the worst case, implying something like wet ice at 32*F). Other logics are possible as well, such as activating when the rate of wheel rpm deceleration exceeds some predetermined value regardless of what the other wheels may be doing. ABS has no way of knowing what grip you have at any given wheel, though the system was designed about some particular value(s). And it's at least theoretically possible for a combination of much grippier rubber and pavement to activate ABS earlier than necessary for that particular combination.

Norm