Abstract: Improvements are disclosed to conventional brake slack adjuster mechanisms of the type which are employed upon heavy equipment such as dump trucks and the like which mechanisms are anchored to the axle of the truck and utilize a worm drive and spline arrangement within an adjuster housing to drive a spline shaft interconnected to the brake assembly to adjust the brakes. The worm drive is driven by a worm drive adjusting bolt which has an adjusting bolt head which interreacts with a spring loaded adjusting bolt head socket lock which may be forced out of disenagagement with the adjusting bolt head to permit adjusting of the brakes by the worm-spline drive arrangement and which adjusting bolt head socket lock upon release engages the adjusting bolt head to lock the adjusting bolt head against misadjustment.