Vacuum in a 2000 F350

THere is a valve in vacum accumulator tank that closes when it is not being supplied with vacum from a engine driven pump (diesels have no vacum themselves) It could be on the break booster too. The fact that power steering is out out to tend to suggest that you have hydroboost brakes not vacum (most 350's have them and about all diesels) and if this is the case, you will not have much boost reserve with engine not running and power steering pump powers steering and brakes on a hydroboost system so if you have one your observations are normal operation.

----------------- TheSnoMan.com

Your brakes and P/S don't work off vacuum

They get feed by the p/s pump and if the engine doesn't run, you don't have pressure

The power brakes should have assist. The hydrobooster has an accumulator that holds pressurized brake fluid. The vehicle should have enough stored pressure for 4 good solid pedal pumps and then start to bleed off, getting harder with each stroke. The system should not bleed down over night. Get it checked. If the engine dies while driving it. apply the brakes and keep steady pressure on the pedal till stopped, or you could run out of assist before the vehicle is stopped. When working on the brakes you are supposed to pump the pedal till hard before working on the system. Be a real bitch to have your fingers between the pads and the damn thing apply the brakes. Even a vehicle with vacuum brake booster should have 2 good pedal pumps before running out of assist, and should not bleed all the way down over night. The power steering on the other hand, engine off, no assist.

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