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Discussion Starter #1
Hi. I already changed the booster and master cyl. Everything went fine for a year and 12,000 miles. How strange behavior, seems like I am losing brake vacuum. When at a stop, the brakes have almost no continued grab. Car starts creeping. When moving, I have hard breaking but not soft braking. Even hard braking is not like it was but will stop the car. But the first inch of peddle does very little. When I pulled the one-way valve out of the booster, there was vacuum in the booster (light hiss--even with engine off). Plenty of brake fluid. 1998 2.7 base 64-k miles. Stumped. Thanks.
 

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One possibility: Check the vacuum hose where it plugs into the plenum nipple. I had weak, lazy boost and when I finally got around to checking into it, it turns out that the plenum end of the booster vacuum hose for some reason had reacted to motor oil (or brake fluid) and swelled up to almost twice its size, was not at all tight on the nipple. Replaced the hose, problem fixed.

You proved that your booster gets vacuum, but is it reduced, or is it slow in re-charging when brakes are used due to restriction (in check valve?) or a big vacuum leak (like with my swelled-up hose)? Hopefully your replacement booster isn’t failing.
 

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Discussion Starter #3
Thanks Peva. Changed the check valve. No help. There is quite a bit of retained vacuum in the check valve when I pulled it. Quite a rush of air comes into the booster, much more than it was before I changed the booster a year back, when there was no vacuum in that check valve. (Engine off both times).
The hose looks fine. I had it off and the fit on the plenum is pretty tight. I do not think the new booster is bad but it could be possible. Could be some oddball master c. issue (also new as of a year ago). If not, most likely the vacuum in the plenum is weak. Looking for other broken vacuum leads. Trying to locate a diagram. Thanks again.
 

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Could be the Master Cylinder leaking at the rear seal into the Brake Booster. Has the fluid level in the reservoir dropped? Have you had to add brake fluid?
 

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Discussion Starter #5
Hi Ronbo: No break fluid missing. Could it be a bad master c? Even though relatively new?
The other two contingencies scare me, another booster replacement (uggg) or manifold vacuum problems (uggg uggg).
Thanks.
 
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