I've had this problem on my '89 CRX for a while now. If I drive really slow for a little bit, I lose brake boost (I assume that's what's happening, the pedal drops almost to the floor and then is really hard but does do something). Doesn't happen at idle or when I'm going faster, just when I'm going very slow. Usually happens when I'm pulling out of the driveway or something, happened once at a really slow turn at an autocross. I'm not sure where to look. Replaced the booster and MC (bench bled), bled everything a ton of times. So I'm thinking vacuum problem, but everything seems fine, car idles and drives properly, etc. I really want to get it fixed before I go HPDEing, anything iffy on the brakes is just bad.


Modified by turbohappy at 7:18 PM 8/23/2004

 

No ideas? Oh well, I was hoping that someone here would have more idea than the EF crew since racers care a lot more about their brakes.

 

If the pedal drops to the floor then it isn't the booster or vacuum supply. Either your MC is bad or you have a leak/air in the system.

Loss of the booster will make the pedal rock hard and increase effort - try pushing the pedal to the floor with the car not running. That is non-boosted braking.

 

 

Yeah that is what I just said.

The pictures are helpful though.

 

I have the same pedal falling to the floor problem, but it usually happens after the engine is under a load, or if I'm on the highway for awhile, and go to get off, I have no brakes.

New bb/mc are going in regardless of this problem, so I'm sure it will be fixed then.


Cute avatars guys.

 

It's screwy. Every test in the Helms seems to pass, I'm not sure where to go looking. With a new booster and MC and lots of bleeding with no change at all, the only thing left I could think of is some sort of weird vacuum issue.

 

You've tested the vacuum check valve, correct?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Xian &raquo;</TD></TR><TR><TD CLASS="quote">You've tested the vacuum check valve, correct?</TD></TR></TABLE>
Yes, it has plenty of vacuum. Engine idles at about 2k RPM with that line pulled off.

 

If it passed all the tests in the Helms I'd check your wheel bearings. If the wheel woobles or deflects a lot when you pull out of your driveway it will push the calipers open and then you'll have long peddle travel when you first reapply.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Shu &raquo;</TD></TR><TR><TD CLASS="quote">If it passed all the tests in the Helms I'd check your wheel bearings. If the wheel woobles or deflects a lot when you pull out of your driveway it will push the calipers open and then you'll have long peddle travel when you first reapply.</TD></TR></TABLE>
Interesting thought. I'll check them. Would it follow that it would only do this at low RPM, not when I'm tearing around an autocross course or going down the highway?

 

From thesounds of your description of the problem (pedal gets really hard) I'd call it a vacuum problem. Your booster is leaking out the vacuum, or its not building any to begin with. At part throttle cruise on the highway, or at idle you are likely getting alot stronger vacuum, but a low throttle, the booster doesn't see much vacuum coming from the motor.

 

He said the pedal drops to the floor. That's not a vaccum problem. Does the pedal come back immediately with one or two pumps of the pedal and then it doesn't give you problems again until the next driveway encounter? If so I'm sticking to the wheel bearings. If the master was failing it would seem odd that it only occurs under certain conditions. Maybe your hitting the pedal harder or maybe softer under these conditions where your master may be failing under one or the other condition. Try sitting in you drive way for a while not rolling and push the pedal hard soft fast slow over and over again for as long as you can handle it. If it never gives you a problem then the master is ok.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Shu &raquo;</TD></TR><TR><TD CLASS="quote">He said the pedal drops to the floor. That's not a vaccum problem. Does the pedal come back immediately with one or two pumps of the pedal and then it doesn't give you problems again until the next driveway encounter? If so I'm sticking to the wheel bearings. If the master was failing it would seem odd that it only occurs under certain conditions. Maybe your hitting the pedal harder or maybe softer under these conditions where your master may be failing under one or the other condition. Try sitting in you drive way for a while not rolling and push the pedal hard soft fast slow over and over again for as long as you can handle it. If it never gives you a problem then the master is ok.</TD></TR></TABLE>
It drops close to the floor. The last 15% of the travel or something like that I have brake, but it's really hard. And it does come back after a couple pumps, no problems again until sometime later.

The MC is pretty new and it never gave me a problem doing your test.

I'll test the wheel bearings tonight, why would this not cause a problem while going faster?