Sudden Brake Boost Loss?

[J. W. Hall]

Hi All. We're talking about a '68 F250 with front disc and rear drum, 3spd Auto, and a booster. One minute I'm driving down the road with what feels like normal booster on the brakes, and the next time I go to stop, it takes about 5 times the pedal pressure to stop, and that's the way it is now. I'm ruling out something I may have done, since it happened enroute--I guess something failed?

Any diagnostics I ought to try? I can hear a vacuum sound when pushing on the brakes--softer at first, then louder with a pretty good application, but if I really press hard on the brakes (I notice this only if I'm stopped and really press hard) the vacuum sound pretty much goes away. (I couldn't tell you if the pattern in the same while I'm driving due to engine, road, wind noise) So, as I press harder, the vacuum sound gets louder and then dies away at full brake application. Sorry that I don't know whether this pattern was going on before the change in breaking--I wasn't paying close enough attention to brakes that were working!

I'll double check vacuum from the manifold, but I was wary of the check valve...does that just pull out of the booster?

Thanks all!

[ToughOldFord]

That vacuum you're hearing is a ruptured diaphragm in the booster. Replace the booster.

[J. W. Hall]

Thanks! I'll do it.

[basketcase0302]

J.W.

Might also want to check the "check valve" (for lack of the proper part name).
The valve where your vacuum line attaches to the booster itself.
Use a mitivac tool to pull a vacum on it to test it for leaking.

Jeff