rithsleeper

Drive an 89 c4 6-speed, upgraded intake manifoldwhile up and running c5 brakes in front with hawk + pads and slotted rotors. Was at Roebling Road and it seems even though I have upgraded my brakes signifigantly I am still not even close to satisfied. Next upgrade will be brake ducting.

Here are my problems, first coming off the front straight i hit 130 and when i brake hard my rear end floats around and its never a hard controlled brake. I feel i have to brake sooner than i should just because of that... any thoughts?

Second i developed a thump that seems to be associated with brakes. It's cadence follows the wheel speed and is slight when driving then shakes the car when i brake now. Im thinking my rotors warped? How can i check this? Where is the best place to buy rotors that can handle this abuse and not warp? I would only be able to spend around 250 for the front pair...

Im also developing tiny hairline cracks on alot of my rotor face, how long do i go before replacing because of this? I see tons of guys not worried about this and say its going to happen, when does it become a problem?

Thanks all for your input.

brkntrxn

The rear end floating around is the suspension setup, not the brakes. My C5Z06 did that until I installed 04 Z06 shocks, moved some weight to the rear, and raised the rear for more stagger.

It is rare for Z06 rotors to warp, they usually are straight until they crack. Are you sure you don't have a flat spot on the tire?

Hairline cracks are normal. Run the rotor until it cracks all the way to the edge. You'll know when it is time to replace them. The crack will be big enough to see at five feet.

-Kevin

CHJ In Virginia

I agree with the above poster, the wandering under braking is most likely suspension setup rather than brakes. Check alignment, rake and weight distribution as well as condition of all tire rod ends and bushings.
The thump is more than likely a cracked rotor. Check both the inside and outside friction surfaces carefully. Also pull the caliper and check the pads for delamination. Although very rare, I have had the pad material separate from the backing plate and rattle around in the caliper. Thought it was a crack but it was the pad.
The rule of thumb I use on rotor repalcementis - if the crack is large enough to catch a fingernail as I run across it, replace the rotor. A lot of folks just wait till it cracks, but I prefer preventative maintenance to changing rotors at the track. They all are going to spider crack from the heat, it's normal.
Get the cooling ducts ASAP.

rithsleeper

Ok, ill check out all the rotors after church today. Ive heard that when my limited slip wears out the diff becomes basically an open differential. Could that be a contributing factor and would that be worth trying to refurbish? Is there a link on how to test all the rear suspension components in the rear like shocks and bushings? Usually if i can wiggle around and feel play thats when i replace but i bet thats too late on the vette.

brkntrxn

A worn diff will show up on track out, not the braking zone.

Jason

HP+ pads won't last long on track. Rotors are consumable, get used to replacing them.

Black89Z51

I am running DBA 5000 rotors and Carbotech XP12s on the front of my 89. I'm also running ducting to the inside of the rotor. I know the pads are expensive but they are amazing. No problems with the rotors.

Try moving your car every few minutes after you get off the track.The pads can hold heat in the rotors causing them to cool unevenly and warping.

c4cruiser

Does sound suspension related more so than braking. Check everything to make sure the bushings are in good shape and all components are tight. What about alignment? Specs?

With the C5 front brake conversion, just use C5 Z06 stock rotors. Rotors (and pads) should be a maintenance item for track days. Do some searching for C5 rotors to get the best prices. I got some Raybestos "Professional Grade" rotors from Rockauto for a decent price. Look at the Carbotech XP10 pads in front and XP8 in the rear for track use.

When you did the brake conversion, did you get and install the Doug Rippie rear brake bias spring? When I did the conversion on my '87, that spring made a big difference in braking performance and helped to balance the braking effort. After installing my C5 brakes up front and before the spring, the rear brakes would start to lock up with even just medium braking effort and the ABS kicked in constantly. Once I added the bias spring, that stopped and the car doesn't squat, brakes hard and no ABS activation unless I brake extremely hard.

If the car is also used for the street, I would suggest that you have a separate set of pads and rotors just for track days. For street driving with my '87, I use AC Delco Z06-specific pads in front and Hawk HP+ in the rear. This combo also works OK for autocross events. I have run this combo at Portland (OR) International Raceway and at Pacific Raceway and it works decently at those tracks. My '87 has the 4+3 trans and with not using the OD, I rarely see speeds over 125-128 on the straights.

rithsleeper

ok, found the warped one I think. My front right rotor. If I spin the tire it rubs slightly then gets hung up at one point pretty good. All other 3 spin with just barely rubbing the pad. I'll have to make sure I move the car a few feet every 2 minutes or so after getting off the track.

DBA 5000 Cost $347 apiece!!!! what? I guess if I was a wealthy ceo and had a dedicated race car... What about the 4000 series? its a manageable 160 a piece...

oh and I also have the bias spring from MidAmerica but I've been reading lately that doug rippie has a different one... Should I move to the Doug rippie?

Is there a reason to go with the Carbotech XP10 over the XP12, they are both about the same price and the xp10 says cars less than 2900lbs. Mine is still basically stock at 3400lbs. So I take it I should go with the xp12?

c4cruiser

I think the Mid America spring is what they get from DRM. I paid $20 delivered directly from DRM. DRM has two versions; one for ABS cars and one for cars without ABS.

Again for rotors, stay with stock rotors. Raybestos and Centric are decent ones. Over the years here, it's been a common suggestion that there is no real need for drilled/slotted rotors. Most will crack around the holes and once the cracks are big enough, they can easily come apart. Just checked Rockauto and they have Raybestos "Advanced Technology" C5 front rotors for $42 each (56700 and 56701).

Carbotech Adam (supporting vendor) recommended the XP10/XP8 combination for my 87 with the C5 front brakes. I was curious about the weight comment on their website, but a number of members here run that combo on their C4's for both track and autocross events. You might want to send him a PM or call and talk with him. Here's some info:
Adam Adelstein
Carbotech Performance Brakes
4031 Dearborn Place N.W.
Concord, NC 28027
216-780-8825
GO DEEP!
adam@ctbrakes.com

jaa1992

Make sure ALL 4 calipers are in the best working order possible.
Put in the DRM bias spring.
Carbotech XP12 on the front and XP10 on the rear.
Make sure all 4 shocks are in good condition.

My C4 brakes almost flat now that I have done these things.
1992, J55 brakes, fresh bilstien shocks, fresh bushings

Racingswh

This is a good read about "warped" rotors.

http://www.stoptech.com/technical-su...nd-other-myths

Adam@Amp'dAutosport.com

Depends on tire, give me call I will be happy to help you.

jaa1992

I love Carbotech pads so much I live with the little squeaks and chirps on my daily driver V6 Camaro. They even brought my XP8 pads for it to CMP for an event where I was instructing. It brakes 1000 times better than the stock pads.
On the C4 I've tried several different manuf and pad compounds, Cabrbotech has been the best performing and most rotor friendly so I'm sticking with them.

I ran XP10/8 combo with street tires and Khumo 710. Street tires I could over brake occassionaly. With the Khumo's it was just a little light as I got faster which I why I went to the 12/10 combo. Now running Hoosier R6's and I really like the 12/10 combo.