GAZ66 brakes

[DougieIrish]

I’ve replaced the master brake cylinder with a refurbished unit by Past Parts. I’ve installed two new brake vacuum boosters. When the engine got swapped out for a Cummins 6BT the guy installing it fitted a 12v electric vacuum switch in the system. Unfortunately after many exciting close mishaps my brake pedal has got to be double pumped to work. I’m not sure where to go with this now hence asking you guys. My master brake cylinder & clutch slave cylinder are both separate & fed off the same reservoir. I’ve bled the system many times using the inner tube system to rid the air. Any suggestions guys ?

[Grommet1]

Have you adjusted the play on the shoes on each wheel. There are two things to adjust, the snail cam which is about half way up the backing plate and the eccentric cam at the bottom. I've never quite been sure which order to do these but I do it with the wheel running free off the ground and adjust until it binds then back off slightly. There are two shoes on each plate to adjust.

If there's too much play the shoes retract too much on the springs so it then takes a couple of pumps to push them back out far enough to engage the drum. The snail cam stops it retracting all the way back.

Cheers John

[Potemkin]

Hiya Dougie,

It is an all too familiar problem with Russian military vehicles. That first press of the pedal normally gives an unpleasant surprise.

If the master cylinder is good I can think of two things to look into. The first is that somewhere there is still air in the pipework and the second is that one or many of your brake shoes isn't quite adjusted enough. This means that when the brakes are off the spring pressure across the shoes sinks the piston back into the cylinder away from the drum and when you press the pedal next time you are taking up the slack thus giving a soft first press.
Have you been round and adjusted them top and bottom? It usually works for us