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Discussion Starter · #1 ·
Hey, any of you other boosted guys notice problems with your brakes after a while?

I tested my brake booster check valve, and it's working, but it seems that whenever I'm boosting now, the brake pedal is super hard to press, and when I let off and it's back into vacuum, the pedal just sinks.

Just wondering what some of your experiences were, if you've found that your manifold pressure is enough to break the check valves.

Or, it could just be a coincidental booster/master cylinder failure, too.....

--sarge
 

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Sometimes you need 2 or 3 check valves in series. But that's not the cause of your problem.

The fact that the pedal is sinking is indicative that your check valve in the diaphragm of the brake booster has worn out. Consequently, you're going to need to repair/buy a new brake booster diaphragm assembly.
 

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Discussion Starter · #4 ·
yeah, Denis, that's what I figured, or else I'd have read about it. It figures, that right about the time I get one thing fixed, another breaks, lol!

I already ordered a new booster and master cylinder anyway, but I was just checking to see if I was wrong. It's probably because 1) the damned thing's 10 years old and 2) it is NOT designed for hundreds of laps around road courses, and especially not for bringing the car down from speeds over 120mph.

I probably did it myself, just by pushing too hard.

ah well, one step closer to the RX7 4-pot upgrade, I guess.... :)

thanks, guys!



--sarge
 

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Yeah I get the super hard pedel feel under throttle while braking and I'm not even FI. I think it has to do with the vacuum booster and not being in vacuum when you are in the throttle.
 

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as long as your one way valve is working right things should be working right. maybe you should bleed your brakes? if the pedal is hard to push down that means you have good brakes.
 

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WOHOO! Steve buddy, you made it to FEOA! How's the scort? :D
 

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Discussion Starter · #8 ·
oh, the brakes have been bled already, nearly fully flushed. Sometimes at track days i've got to bleed them twice or more, just because I keep boiling the fluid... but i think i'm putting so much pressure on the pedal at times, like when the fluid is boiled and it goes to the floor anyway, that I probably tore the diaphragm inside the booster at some point. since I've got basically brand new calipers all around anyway, i figure doing the booster/cylinder can't hurt either. What I'm hoping to NOT have to do is re-line the whole car. If that happens, I think i might just go with a dual-master setup with a proportioning valve, like from wilwood or something.

--sarge
 

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SgtRauksauff said:
that I probably tore the diaphragm inside the booster at some point.
The diaphragm isn't torn. If it were torn, then the brake pedal wouldn't sink under vacuum like that. And likewise, it wouldn't be hard to press under boost either. It's the poppit valve in the booster that probably got foobared.
 

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^^^ I agree with sirigan. The booster diaphragm isn't torn. If it were, you wouldn't stop. I disconnected my brake booster from the engine and tried to drive with it once to look for a brake problem. It's a good thing I didn't take it out on the road because you cannot stop worth crap all if there's no vacuum in the booster. If it were torn you wouln't hold much vacuum if any.

My suggestion is master cylinder. I had very inconsistant brake pedal pressure/travel/feel etc. to the point where it sometimes had me wondering if I could stop 8O The master cylinder made the single biggest difference when I changed mine. A brake fluid changed helped, but not much at all compared to swapping the master cylinder. If it's still the original I'd say you're about due for sure.

Good luck :wink:

Matt 8)
 

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Discussion Starter · #12 ·
what sort of check valve is that, or where'd you get it from? I looked around at a few auto part stores around here, and couldn't find anything except small little vacuum hose checkvalves, nothing big enough for a brake booster.

--Sarge
 

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if you keep boiling off the fluid, you should consider having the system flushed again and this time refilled with DOT 5 silicone fluid.
 
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