Your brake calipers have pistons that can after years of driving and not properly flushing the brake system become frozen. You may also want to replace the brake hoses at the same time as they can sometimes produce locked brakes as well.
Be sure to change both front brake hoses. I didn't and my calipers would lock up.
Front caliper piston seals are gone can get kit for 35 bucks
Inspect your calipers make sure pistons are working
Check the pistons inside the calipers, usually they are the reason brakes lock up.
When you hit the bump and you have the brakes applied, the tire will lock up when the tire is air-born for a moment.
caliper froze, brake line collapse, or wheel bearing out.
If it is an older car without ABS the brakes would lock up and the car would slide/push/unable to steer, unless you got on/off the brakes. With ABS the computer would pulse the brakes and would prevent lock up so you would be able to steer.
it might not have enough brake fluid or your ABS is going bad. i would take it to a shop cause that can be serious.
Improperly adjusted, new pads, low traction, etc.... most vans only had rear-wheel antilock brakes.
The brakes my lock up without touching them if a foreign object has become lodged between the pad and the rotors. A failure in the hydraulics may also cause the brakes to engage on their own.
Rear drum brakes, that lock up during heartbreaking quicker than the front brakes, can be adjusted. The rear brake pads need to be backed off.
Slam on your brakes. If your brakes lock up, then you do not have ABS. If your brakes do not lock up and you hear a knocking type of noise from your brakes, then you have ABS.