[skypilot17]

Hi Rod,

Yep, a loose bearing will do it. The GM clearance spec between the reluctor (the gearlike toothed ring that is mounted on the axle or rotor) and the sensor itself is .45mm to 1.25 mm. That's about 1/32 to 1/16 inch. Anything outside that will generate wrong electrical pulses that go to the ABS controller. Pulses that are too long or too short or missinig or random give wrong information to the ABS controller and it reacts by turning on at the wrong times. There is a good explanation of this at
http://www.brakeandfrontend.com/wheel-speed-sensors-abs-and-tcs-signal-use/

BTW, in 97 Blazers, the reluctor ring on a 97 Blazer is machined into the wheel bearing assembly. So when you replaced the wheel beari[ng asembly, you also replaced the reluctor ring with a nice shiny, sharp new one.. I'm sure that helped a lot.

As computers go, the ABS controller is pretty tame. It has just enough programming to detect the signals and react. What it -should-do is turn the ABS light on whenever the pusles are wrong. Instead, it generates DTCs that you have to check with a scan tool or a laptop and a plug that hooks the laptop to the OBDII plug. BTW, that is what I use. The plug and softtware cost me only $250. It paid for it self the first time I used it. Any time you get a check engi[ne light, it displays the DTCs and tells you exactly what is wrong. www.autoenginuity.com.

BTW, my Blazer had exactly the same symptoms as your dads. The pump would turn on when I was alomst stopped and would not turn off until I released the brake and then braked again.

The biggest problem with the sensors is that because it they are magnetic, they attract metal shavings from metallic brake pads or shoes. When enough shavings are piled up around the magnet, the sensor no longer generates a big enough pulse and the ABS does not work right. Simple solution: Clean the sensors on all the wheels every few months. Wash all the dirt and metal particles off both the sensor and the reluctor (speed ring) and blow dry with compressed air. Depending on the installation, you might have to pull the rotor off to get at the speed sensor.

BTW, some guys might wonder how come a woman knows all this stuff. Well, I am a mechanical engineer and a long time ago, I used to work for GM. :-)

Cheers,
Diane (skypilot)