Apparatus for use with vehicle electro-pneumatic brake systems, said apparatus being characterized by a friction-free self-lapping valve device responsive to opposing control forces reflecting the degree of electrical dynamic braking and the degree of fluid pressure controlling the pneumatic friction braking for automatically maintaining the called-for overall braking effect of the dynamic and friction braking combined, said valve device being operable responsively to variation of dynamic braking effort for automatically maintaining the called-for electro-pneumatic braking relationship by compensatingly varying the degree of delivery fluid pressure for the pneumatic braking system.