Formula1996

iTrader: (7)

I recently (9 Feb) participated in a track day at the Streets of Willow in my T/A, we ran the full course clockwise including the bowl. Top speed was around 95 mph on the front stretch and the back stretch. Anyway, as I started pushing it up, (as this was my first time on a real track) I began to notice what I would consider to be a pretty severe brake bias problem. Anytime I attempted to brake aggressively the rears would lock up and the rear axle would go into a severe hop. I nearly ran off the track sideways the first time I did this going into turn one off of the front straight away at about 80mph, got the car pretty bent out of shape but managed to recover. I took it easy on the brakes the rest of the day cause every time I tried to brake hard it would induce wheel hop and lock the rear brakes up, even at lower speeds. Has anyone experienced this problem before or know what my problem might be? My brakes are completely stock and the only thing that I can think of that I've done to the car that might affect this is the torque arm (mods are in sig). I didn't have it dialed in correctly at the race and I think I was running about 4-5 degrees of negative pinion angle. I've since adjusted it to about 1-2 degrees of negative pinion angle, but have yet to attempt to see if this has helped. Otherwise I'm clueless as to where to even start looking for the problem. On a side note I never saw any brake fade, which I thought was proof positive I was unable to brake hard during the day. Thanks for any help you guys can give me.

getusumws6

iTrader: (9)

sounds like you might need to add a brake proportioning valve, then you can fine tune your brake bias'

Killer_Bluebird

iTrader: (23)

The torque arm angle will definatelly help as that much negative angle preloads your rear suspension too much. Proportioning valve will be an option. I and other just minimize the problem by running crappy cheap stock brake pads in the back and more aggresive race pads in the front. For instance I run Carbotech XP10 in the front and stock duralast or similar in the back. What happens is that as heat builds up on the rotors the rears will glaze and while the front race pads become grippier when they get to their heat range, so the front to rear bias becomes much better. But that is really a band aid fix. A proportioning valve is probably a better way to reduce the problem.

Viper

iTrader: (6)

Yea, that was way too much negative pinion in the torque arm. I run -2 and don't have brake hop.

Formula1996

iTrader: (7)

Thanks guys for the info!!!

I def plan on purchasing new brakes, prob Hawk pads to start off with for the street, I am considering Strano's break package right now as an option, but like you said, I really only need the front pads.

That seems to make since with the pinion angle, but a couple of other thoughts came to mind today at work:
What defines NEGATIVE pinion angle? Is it the front of the diff pointed up towards the bottom of the car or down at the ground? (this doesn't' seem to be talked about much, could be a good reason why, and I'm just missing it)

How does rotating the diff (changing the pinion angle) affect the suspension preload? Is it increasing the preload seen at the springs or maybe the bushings in the LCA??? I've read threads that will argue that changing your pinion angle to anything but 0 (which is supposedly what it's set to form teh factory) only binds up your drive train.

Could my ABS play a role in the rear brake bias problem? I kinda doubt it but I'm not going to rule anything out.

Viper

iTrader: (6)

Check out the video on the front of BMR's website that shows pinion angle.

Formula1996

iTrader: (7)

I have watched that video many times... It's not a very in depth presentation on how to install one. However it is just enough info to get you going in the right direction (I hope).

u118224

iTrader: (3)

Did you get your brakes fixed? I wonder if the problem was 1) old brake fluid or 2) air in the lines. I don't think it's a bias issue, the system generates the same pressure front and rear. For future track duty, I would flush out the old brake fluid and put in a fluid with a higher wet boiling point, and make sure the brakes are bled properly.

Road courses are brutal on brakes. I suspect the fluid may have been the culprit. Eliminate the cheap, easy fixes first. Then move up to better pads and rotors. Just my .02. Any other thoughts?

BMR Tech

iTrader: (9)

Which type of torque arm do you have on your car is it a long replacement style arm or one of the floor mounted units?

Cap'n Pete

iTrader: (2)

You've never taken your car on a road course before, have you??

Rear brake hop is a HUGE problem on LS1 cars. Way moreso than it ever was on LT1 cars, apparently.

If you really get into road racing, check out www.frrax.com ... it's all F-body specific race tuning and setup discussion .

I've experienced brake hop quite a few times with my car. So has a fellow competitor of mine, also with an '02 Z28. It has nothing to do with bad brake fluid ... it's got a lot to do with not enough front bias (read: too much rear bias). It can also be affected by suspension components, ie: soft rubber bushings (crap) vs. poly vs. rod-ended (best). Pinion angle and LCA angle can/do both have an effect. Too much negative pinion is bad, but "proper" pinion angle doesn't prevent it either .

This year, I have "hardly" suffered any brake hop (a couple occasions, but much less than the last couple of years). The big change(s)? Well, a lot of things!

- Strano springs w/Koni 4/3 SA shocks.
- poly / rod-ended LCA's.
...and the things that help(ed) the most?
- Hawk HT14 pads in the front, and regular street pads in the rear.
- Hoosier R6's!

Basically, having a very aggressive pad in the front adds that much more bias to the front of the car. And the stickier tires are much harder to lock up, so the net effect is little or no brake hop .

My friend with the other '02 Z28 installed a proportioning valve on his rear brakes this year, but he's still been suffering brake hop. However, he's running a slightly less aggressive pad (HT10's vs. my HT14's) and he doesn't have aftermarket rear LCA's (apparently the stock rubber bushings act like "springs" of their own, and don't help the problem when the rear wheels start hopping).

In the meantime? "Band-aid" the situation by braking earlier/lighter. Unfortunately, it's the only, uh, cure?

mitchntx

iTrader: (14)

All the physical changes to the car as outlined above are great ideas to help. I never actually rid myself of rear hop, even after adding a great set of rear shocks, rear bias valve, mismatched pad compound, etc.

I was reading a book called "Speed Secrets" and came across this little nugget ...

Squeeze the brake pedal on and off

And after watching a LOT of my own in-car video, I saw a pattern emerge ... I would get all my rear wheel hop on an aggressive braking move and an immediate down shift.

So I worked on the driver and not so much on the car.

I began being easier on the brake pedal. What I found was that I had a LOT more control under braking.

I also began down shifting a LOT later into the braking event.

Since then, I've never experienced any rear hop.

Check it out ...
http://www.lawmotorsports.net/vids/T...GoProDemo1.wmv

Cap'n Pete

iTrader: (2)

Interesting points.

I've begun to notice that too, that it's on the really harsh brake applications that it usually occurs ... basically, (in my own terms) I'd say it's like "shocking" the system.

There is one tight corner at one of our local tracks that I hopped into about ~4 or 5 laps in a row. Nowhere else on the track, except this one corner. But it's probably the corner with the fastest entry of any on the track, AND it's one of the tightest corners to boot . To add to that problem, the pavement isn't smooth and even in the last section before the corner ... another piece of track (for a different track layout) crosses at 90° to the direction of this layout, so there are TWO "bumps" in the pavement right in the midst of the braking/down-shifting zone . I think that just exasperates the problem :o.

I also remember reading on FRRAX in one of the brake hop discussions, that pushing the clutch in during brake hop will often stop the hopping instantly ... I've actually tried it once or twice (during practise sessions) and it's true!! I deliberately induced brake hop, then stabbed the clutch in, and the car settled almost immediately ...

... not that clutching and braking simultaneously into every braking zone is the most efficient way of getting around a race track, because then there's the issue of the harsh re-engagement of the clutch .

mitchntx

iTrader: (14)

Just to clarify ...

The camera car in the video above is a CMC2 prepped car, meaning it has a stock LT1 and torque arm, Koni SAs, rod ended LCAs that I built myself.

And I would induce RWBH every time at the corners shown at :38 and 1:00

Hear how late I down shifted? While I have softened the way I get on the brakes, the biggest difference is a very late down shift.