I have an 03 Z06 and I am running C6 Z06 calipers and RacingBrake rotors on all four corners. My issue is that my front passenger brake will lock up well before the others and activate ABS way too easily. Obviously this causes some handling and "feel" issues during aggressive driving. In addition I have had the same issue with ABS deactivated so I don't think it is a wheel speed sensor, but I could be missing something. Any input would be appreciated.

 

First, any problems with the electronics of the braking system will set a DTC. Pull the codes and list them here and someone can look them and help you diagnose the problem.

Second, if your ABS is turning on "early", sounds to me like you have "over braked" the car. The limiting factor in deccelerating a car is the friction between the tire and the road. Big brake kits are only useful when you are at the race track (road course) where the bigger brakes can better deal with heat (less fade) and because a "race car" usually has BIG and STICKY tires the larger brakes will help the car stop sooner than the stock brakes. For a car with street legal tires the stock brakes are more than big enough. Any Corvette can turn on ABS with the stock brakes ... that means the brakes can generate more stopping force than the tires can handle. You're generating too much brake torque and you're locking the wheels to soon. Also, you may be "snap" braking ... basically that is "stomping" on the brake pedal. You should "step" onto the pedal. The difference is that when you stomp on the pedal the brake pressure rises so fast that the front tire(s) lock before any significant weight transfer occurs. By stepping into the brake pedal that split second difference causes weight transsfer to the front wheels to occur as brake pressure is rising, allowing the front wheels to betteer grip the road for better stopping.

 

Thanks for your input. FWIW I am running pretty sticky tires when I drive on the street. At any rate, my issue is not with the ABS activating, it is with the fact that the right front brake behaves substantially differently than the left front brake which leads me to believe there is a difference in the way they are functioning. For example: With ABS deactivated, at 100mph in a straight line and an aggressive but not snappy application of the brakes, the right front caliper will lock up and the other three will not. You can imagine what this does to the balance of the car at speed. If both brakes reacted the same to input I would not have any issue. Also, to avoid the lock up I have to brake very carefully, depending on the conditions and attitue of the car.

 

Again, the first thing I would do is check to see if any DTC are set. The EBCM is responsible for managing brake bias (Dynamic Rear Proportioning - DRP) and if it is having a problem a DTC will be set.

I don't know how (or why) you're disabling ABS but ABS is a function of the EBCM, and the EBCM controls several other functions such as DRP, Magnasteer, Active Handling, etc. Your "disabling" the EBCM may be contributing to the problem.

You may have a mechanical issue ... for example if there is a kink in the flexible brake line to the LEFT caliper, pressure may build faster in the RIGHT caliper ... leading to your problem. Debris partially clogging input of hydraulic fluid to the left caliper could do the same as a kink in the line. If the "padlets" on each rotor aren't matched as far as pad material type, you could get uneven braking.

There's dozens of things that could contribute to uneven braking ... even alignment, or a bad wheel bearing can make a difference. A complete inspection of the brakes and front suspension will need to be performed.

Again, check for DTC first, the computers may point you toward the problem, making diagnosis somewhat easier.

 

To clarify I didn't disable the abs, I had the EBCM off for repair and still had the problem. This led me to believe (obviously) I had a mechanical problem, not a computer interface problem. I don't have any TCS or EBCM codes so I am chasing a mechanical problem.

 

You have a dual diagonal brake system. That means the left rear and right front brakes are on the same circuit while the right rear and left fronts are on the other circuit. Thus, there are two ways to look at this. First, lets assume the right front brake is working as it is supposed to be working. That means the other circuit isn't getting enough fluid pressure to the left front caliper to cause it to lock. That could be because there is a problem in the master cylinder or all 6 pistons in the caliper are sticking in some way keeping them from applying enough pressure to the brake pads. This condition also makes me wonder why the left rear wouldn't be locking as well. Rears usually tend to lock first due to weight transfer.

Second, lets assume the right front isn't working as it is supposed to. The master can not apply any more pressure on this side than what it is designed for. If the right front caliper is locking pre-maturely then there must be more friction at that point Vs the other 3 wheels.

What does all this mean? One, it is possible the brake pads are not all the same compound. This could happen with brand new pads due to a manufacturing mistake. Two, the master cylinder has something wrong with it. Three, there is a blockage in the brake circuit for the left front wheel that is reducing brake pressure or there is a leak or air in the lines for that circuit. Four, there is a problem with the left front caliper.

I would start with bleeding the brakes especially the right rear and left front. Not sure what the bleed sequence is on the GM calipers but on my Wilwood 6 piston calipers the outside caliper half is always bled first followed by the inside caliper half. If that doesn't solve the problem then check the master, followed by trying to figure out if the pads are all the same compound.

Bill

 

Exactly the info I was looking for. Thanks Bill.

 

I'd concur with Bill. Anytime someone complains that one side is locking up they usually assume that side is the problem. Often it's the side that's NOT locking up that proves to be the culprit. Review the plumbing, bleed the LF and while there be certain there are no pad hang up issues and that they are moving under pressure without any binding.