98 Yukon Brakes

Have you had the brake fluid changed lately? Within a year or two, brake fluid can absorb enough water out of the atmosphere to be almost 50% water. This greatly detracts from braking ability. How about the brake hoses? The rubber lines can degrade inside and collapse, causing them to form a sort of one-way valve -- they can either stick, or lock up like this. I'd suspect the calipers or another mechanical component. Have the brake system checked out by a mechanic who can do a fluid pressure test of the braking system.

Yeah. Changed the fluid in Nov. Used good quality dot3-4. Hoses, no, did not replace--good thought. Did replace the rear wheel cylinders. But did not rebuild the fronts. I use anti-seize on the sliding shafts.

I know this is an old post... but, i have an answer. It MAY need new front Wheel Speed Sensors. common problem with these trucks. You need to remove the front wheels, brake calipers, and rotors. once the rotor is removed you'll find a sensor held to the hub with a 'allen' head bolt. what happens is corrosition builds up under where the both is and causes the sensor to bend. remove the sensors, carefully sand the mounting surface and apply a small amount if dielectric grease and install some new sensors. there is a GM bulliten about it.