brake question

[jweb]

Originally Posted by nvrdone

that all makes sense. but this check valve - is it a 90 deg kind of fitting that plugs into the booster on one side & then the hose to the intake goes to the other side? if so, ive got that on the booster

Yes that's what you're looking for. Remove it and try blowing through both sides. Air should only go one way.

[nvrdone]

ok, I will try & check it this weekend. if that's what's been causing this problem for so long, you can imagine what I might say. details to follow ......

[dwcsr]

The purpose of the check valve is to reserve enough vacuum to have 1 or 2 applications of the brakes should the engine shut off or stall. It has nothing to do with pedal travel or operation of the unit other than keeping a reserve of vacuum. When the pedal goes to the floor you are not pushing enough fluid to the wheels to force the pistons out to resistance.

Only two reasons for this, air, or not enough volume, i.e. a 1" bore and you need a 1.125 or 1.25, Residual valves don't do anything for your issue. They are for when the master cylinder is below the level of the wheel cylinder, or if you get a POL or CPP kit and they want to cheap out on the master and not sizing it correctly.

These are simple systems that we want to make complicated, Its push a piston and move another piston via fluid. that's it. You need volume to move it and pressure to keep a clamping effect applied.

No volume no movement. No volume leaves you with not enough pedal. Not enough pressure leaves you standing on the pedal to stop.

Unless your pedal moves to the floor by itself while running or is rock hard and is difficult to apply the brakes the booster is not the issue. Its only an assist, there is a direct connection between the master and the pedal in case the booster fails or the vacuum depletes and you need to stop.

I get this call weekly on our disc brake conversions when they use a POL or a CPP master/booster unit. The cylinder they supply is just to small to get the pedal you want. 1.25" is the largest cylinder you can get into that boost unit.