gotta brake problem,(53 olds), changed most of brake components , with car running;step on brakes when car is in motion ,car stops abruptly;almost throws you threw the windshield .Can`t find a nos check valve for sale for this 53-98 nowhere; could this valve be the problem? Thanks to all who help [img]images/icons/confused.gif" border="0[/img]

If the brakes are drums and the drums were machined oversize it would cause the shoes to "overcenter" and cause the symtoms you describe. Most Drum brakes are self energizing and if the drums are oversize the shoes will pull themselves into the drum face during actuation causing them to lock particularly at low speeds. Measure the drums to make sure they meet spec, even 0.010" over size is enough to cause this.