Q: I have a soft brake pedal problem on my 2006 Ford F-150. I've read several posts about the brake actuator rod being the cause. I removed the two nuts holding the master cylinder in place, but it wouldn't come out. I pulled really hard and it made an air suction noise and popped out. Did I break something in the booster?
A: Probably not. Before removing a master cylinder, you need to release the vacuum stored in the brake booster. Even with the engine not running, reserve vacuum is maintained in the booster by means of a one-way check valve located in the vacuum hose between the intake manifold and the booster. This reserve vacuum is a safety feature that provides drivers with a couple extra power-assisted applications of the brake pedal after an engine quits. The easiest method of releasing the vacuum from the booster is simply pumping the brake pedal several times (engine off) until the application becomes hard. There will be a noticeable difference once the vacuum has dispersed. Then remove the master cylinder. It should come out with little force.
As far as adjusting the master cylinder actuator (push) rod is concerned, Ford had some issues with several models, including the F-150. There have been complaints about a low or spongy brake pedal that doesn't get fixed after replacing pretty much the entire brake system. Be sure you've checked everything else before messing with the pushrod adjustment. Make sure there's no air in the system, that the master cylinder is good, and that there are no binding caliper sliders, excessive clearance between caliper piston, pads and rotor, etc. To do it right, there's a special tool to set the pushrod distance extending out from the booster with the master cylinder removed. But a lot of folks just do it by trial and error. Remove the master, turn the rod adjustment out about half a turn, reinstall the master, and see how it feels. Just be sure to confirm all wheels spin freely by hand after the final adjustment. Going too far out on the pushrod will put a drag on the brakes.
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