Spongy brakes
Thread Starter
Joined: Oct 2002
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From: Jackstandican
Spongy brakes Brakes were working fine one day. Didn't drive the car for awhile and now they're spongy. No issue with soft lines when pressing on pedal. MC reservoir is full. No leaks anywhere. Took MC off booster and it's not leaking into booster. I can't believe air just decided to introduce itself into the system. I'm thinking somehow the MC took a dump, but am not sure. Thoughts?
Hmm I was going to say a leaky seal but it sounds like you ruled that out. How old is the fluid? Did you bleed it again? My mom complained of a spongy brake pedal out of the blue recently and after a full flush and bleed using a Motive powerbleeder and fresh dot 4 it's perfect again. I think the old fluid had too much water content in it and maybe even boiled over leading to the spongy pedal. Similar issue with the wife's car, I adjusted her rear drums and it got better so perhaps maybe a piston or guide pin is getting a little seized up on one of the calipers and not allowing the pad(s) to compress fully. Hope that helps.
Thread Starter
Joined: Oct 2002
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From: Jackstandican
I'll go the cheapest way first and just bleed the entire system. Brake fluid was new, but has been sitting in the car for two years. Perhaps it's contaminated. Just can't figure out why it'd be working fine and turn to **** so quickly. I do have a power bleeder so it'll make life much easier.
I'll go the cheapest way first and just bleed the entire system. Brake fluid was new, but has been sitting in the car for two years. Perhaps it's contaminated. Just can't figure out why it'd be working fine and turn to **** so quickly. I do have a power bleeder so it'll make life much easier.
Thread Starter
Joined: Oct 2002
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From: Jackstandican
Yeah I hear ya. My mom's car was the same, pedal felt great then one day out of nowhere got spongy. Two years on the fluid really isn't too bad. Not sure what fluid you currently have in it but I do know some of the expensive ultra high boiling point dot 4 fluid goes to hell after a year or two. Who knows maybe new fluid and a bleed will do it. Power bleeder is the way to go, can't stand that pumping the brake pedal ****.
checked and rechecked.
TECH Resident
Joined: Jun 2013
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From: Kernersville, NC
If we are talking the Motive unit, 10 psi is plenty. I blew apart my master cylinder reservoir when first using mine. Major mess.....had to touch up paint quite a bit of the engine bay after that.
http://www.camaroz28.com/forums/susp...ploded-691887/
Me trying to go by the factory manual psi recommendation was not smart as it uses a different bleeding system.
http://www.camaroz28.com/forums/susp...ploded-691887/
Me trying to go by the factory manual psi recommendation was not smart as it uses a different bleeding system.
Last edited by ACE1252; Sep 27, 2016 at 12:09 AM.
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I've used between 7-15 psi. Like pointed out, 10 psi would work fine. I prefer to do it dry by not filling the motive with any brake fluid, prevents a potential mess. I just hook it to the reservoir and pump it up. When the fluid is getting low in the reservoir I'll unhook the motive and fill the reservoir back up. I did my LT1 the other day and the reservoir goes dry quick so gotta watch out for that.
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From: Jackstandican
Last time I used 10lbs the cap blew off the reservoir and sprayed fluid everywhere. 
Fortunately I was able to get it cleaned before it did any real damage. I may have screwed the cap on wrong. Who knows.
Fortunately I was able to get it cleaned before it did any real damage. I may have screwed the cap on wrong. Who knows. Thread Starter
Joined: Oct 2002
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From: Jackstandican
Fluid in the rear brake lines was discolored and there was air in the front. Seems to be good to go for now. I couldn't put more than 5lbs in my bleeder or the cap would start leaking.
Nice man, glad it was an easy fix. My Vette wouldn't take more than 7psi, that Motive GM adapter is definitely not perfect.
Thread Starter
Joined: Oct 2002
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From: Jackstandican
Well, thought it was fixed, but to no avail. Pedal are hard as **** now. Seems the range has been cut in half like there is something blocking the pedal. Did the booster test where it was pumped up w/ the engine off and it held good pressure. Started it and the pedal depressed to the point where it would stop so it would seem there is vacuum. Because the system just suddenly had air in it and now this limited motion on the pedal after the brakes were bled I'm thinking the M/C is fooked.
TECH Resident
Joined: Jun 2013
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From: Kernersville, NC
What brand MC did you replace it with? I replaced mine years ago with an AC Delco and the thing has developed a slow leak around one of seals(dripping down the front of the booster)...so I'm going to have to replace mine fairly soon.