312.Z28

I recently bought a 1996 Z28 from an auction that has a few issues. I've poked around the forum and didn't find exactly the same situation as mine. My ABS and traction control lights are on. I've found that this car has a Hypertech chip and possibly a different rear end gear. It has a Summit Racing cover on the rear diff so I'm assuming there's a different gear in there? I haven't dug in too deep yet. Could a different rear end gear or the hypertech chip be causing these systems to not operate? There is also an SLP brake control package installed. The parts in the brake line are still in place but the wiring and switch were all sitting in the glove box when I got the car. I kind of doubt this is the source of the problem but figured Id mention it.
I've also read around and cleaned the sensors, checked the ground and replaced the one burnt out bulb in the third brake light. No dice on any of them.

Injuneer

Welcome to CamaroZ28.com!!!

Let's start with the basic question - does the car have both ABS and ASR (traction control)? ABS was standard, ASR was optional. If you have ASR there will be a black servo box on the driver's side valve cover, a wheel speed sensor on each end of the rear axle assembly, a switch on the console to turn the ASR off, and RPO code "NW9" on the service parts tag in the glove box. Some people see the "LOW TRAC" light, and assume it means the car has ASR, but that light comes on when the ABS activates in non-ASR cars. The traction control option also provides the "ASR OFF" light, which I assume is the light you are indicating is on.

I'm not aware fo an SLP "brake control package". SLP sold a module that modified the operation of the "ASR OFF" switch. By default, the ASR is active when you start the engine, and can be turned off by using the factory switch. The SLP module reversed the function of the switch - ASR would be off when the engine started, and the factory switch had to be pushed to turn ASR on. That may be what is sitting in the glove box, uninstalled. It would not be causing the "ABS INOP" light, but could possible affect the "ASR OFF" light if the wiring has been altered and the module not installed.

Or, SLP may have offered a "line lock" kit, installing a solenoid in the front brake line, to allow rear wheel burnouts. Is that possibly what you are seeing when you indicate "The parts in the brake line are still in place"?

Another question - is the "BRAKE" light on? That light indicates the e-brake is on, but it also indicates there is a problem with unequal line pressures for the front and rear braking circuits. That light will trigger "ABS INOP" light.

To save time and guessing, best thing to do would be to have the EBTCM (electronic brake and traction control module) scanned for codes. A dealer can do it with a Tech-2, or there are now OBD-2 scanners that will also read the ABS/ASR codes.

As far as the "Hypertech chip", there is no removable chip in the PCM (computer). Hypertech sells a "programmer" that attached to the ALDL connector under the dash temporarily to flash program the fixed chip. Hypertech also makes a module that plugs in between the harness and the PCM and provides minimal performance changes. Neither system is very good, providing limited gains, and in some cases, dyno-proven loss of power.

The diff cover doesn't necessarily indicate the gears have been changed. Does the speedometer appear to indicate the correct speed? If the gears were changed, the PCM may have been reprogrammed to correct for the new gear ratio. If that is the case, the gear change would not affect the ABS or ASR.

Best thing to do would be to put the rear on jack stands, mark a tire and the driveshaft with chalk, rotate the rear wheels on full turn, and count the revolutions of the driveshaft. That will give you the rear axle ratio. Or pull the cover and count the teeth on the ring and pinion gears.

If your car is a 6-speed manual, the stock gear ratio is 3.42:1 (RPO code GU6). If you have the 4-speed automatic, it came with either 2.73 (GU2, base car) or 3.23 (GU5 performance rear axle).

312.Z28

The car does have traction control. I'm going to double check when I get home but it has the button to turn it on or off. The SLP kit I was referring to is the line lock kit. The solenoid is still installed on the brake lines but nothing else is hooked up to it.

I am only assuming about the gear at this point, simply based on the new cover and the way it drives. I haven't driven any other LT1 6 speeds but it just doesn't feel stock to me. I don't know if a different rear end gear really makes a car feel a lot different when driving it? The speedo seems to be accurate. I do have to take this car in somewhere to get it looked at but I was possibly going to sell it and didn't want to drop a ton of money into it. Thanks for the help, I'll have to investigate more on my own and go from there.

Injuneer

Changing the rear axle ratio to a higher numerical ratio increases the torque available at the rear wheels. Also means you reach redline on the tach at a lower MPH in each gear. Going with a 3.73 gear in place of the 3.42's will make it feel like you added 9% more torque at the rear wheels, at least on launch. Going with 4.10's will feel like 20% more torque at the rear wheels.

My car was originally an M6, and with the stock 3.42:1 rear axle ratio and 245/50-16 tires, it was turning 1,600 RPM at 70 MPH in 6th gear. When I swapped in 3.73's it would turn 1,750 RPM at 70 MPH in 6th gear. With 4.10's you would see 1,920 RPM.

312.Z28

Here's one of the parts that came in the glove box. Not sure exactly what it is.





As for the gears, I'm going to investigate this weekend and see what I find.