Brake Booster rebuild - how reliable?

My brakes were not working very well and I sent my brake booster and master cylinder to White Post Restorations for a rebuild, on the advice of my mechanic. He said the booster was leaking.

Got it back and installed, and the brakes are still very weak - I'd say even worse than before. I have good vacumm going to the booster. My mechanic says he believes the booster is still not working right and thinks the diaphram isn't working. The engine seems to run better when the vacumm hose is disconnected from the booster, which he says could indicate the diaphram is collapsed.
White Post Restorations did the rebuild, and I know they have an excellent reputation. How likely is it they didn't get it right?

Before I have him remove the booster again and send it back, is there anything else I can have him check or a test to verify the booster is definately not working?

Thanks

 

I'm not sure, but most cars also have a one way vacuum valve that uses intake manifold vacuum to work. Check to see if your Ferrari has one. If it fails internally, it looses vacuum.
Charles

 

Or the valve may be installed backwards.

 

If the cars tone changed when the hose was taken off, it means air is getting to the engine, and all is well. Thats the way it "should" work. The one way valve is at least installed in the right direction, or no air at all would be getting through. The next question is if the valve holds pressure after shutting off the engine, which is very simple. Run it, shut it off, count to 100 and pull off the hose. If you hear air go "whoosh", the valve works. Next problem...

Its been years since I took apart a booster, was way back when I was 17 and I forget most of it, but there are some things I remember. There is a relationship between the booter and master cylinder distance as well as the stroke distance that must be accurate. If the brake pedal moves to far, you will possibly lose all your vacuum boost. Also, if it does not move far enough, you get some of the same effect. There is vacuum on both sides of the diaphram until you push down and open a valve inside the booter. This allows air to enter the back side, and with vacuum out front, it "assists" your effort. Once you let up, the valve is closed, and vacuum from the front is allowed to equalise both side once more. After you shut off the car, pushing the brake pedal should cause you to hear some air in the brakes, and repeated applications should give lesser amounts until it goes away. This would answer if the diaphram or some other part such as the hose from the engine were leaking. But having had the same problem after replacing the booster with one that was overhauled, would send me off to look over everything else in the system before going back to the booster.

When you step down, car shut off, the pedal should be rock hard after the initial "play" is taken up. If you can push down and feel the pedal "give" or "spring" under pressure, there is air somewhere in the system and you need to bleed the system. Even with the car running, the brake pedal should be fairly solid, with only a limited amount of "give" as you apply pressure. If the pedal yields under force and goes down any considerable amount, you have some issue that needs attending. And dont be afraid to ask another mechanic to look it over, maybe the other guy is missing something, maybe being overwhelmed by all that exoticism in his presence.

 

Not to throw stones, but it seems 4 out of 5 Europa guys who use White Post for Girling boosters had to return them at least once. I would never send any of my parts to them and your mileage doesn't seem to vary. I'd send it back and have them fix it; sounds like a leaky diaphram. Boosters are difficult to rebuild correctly; I know a few guys who have done their own and they say it's not fun.

Ken