Ok so if I put on the brakes at first the pressure is fine, but then if I let off a little and then push them back down I lose pressure and the pedal gets closer to the floor. At that point there is steady pressure, but then if I let off a little again... it does it again till I get to the floor. At which point I still have braking power, BUT it's not right SO.

I've tried this so far, only happend today and I've only worked on it an a few minutes so not a long list.

-Checked resevoir and it's full.. almost black brake fluid though.
-Changed vaccuumvalve thingy going from the booster to the Plenum.
-Looked for leaks around the resevoir hoses.

Hope you guys can give me some insight

Thanks
-Chris

 

Probably your brake master cylinder. I'd change that too. It's not hard and they're pretty cheap.

 

Did you try bleeding the brakes?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dre2day &raquo;</TD></TR><TR><TD CLASS="quote">Did you try bleeding the brakes?</TD></TR></TABLE>

Yeah not 100 percent sure how the boiling part on brake fluid works. But once you boil that fluid, it gives you a mushroom feeling

 

It just happend one day and was fine the day before so I don't think it's boiled fluid. Plus I didn't do any hard braking. I'm just going to swap out the MC with the one from my broken car and see if that helps. I just don't want to stay up late fixing this outside of my garage because my broke car is in the garage in the cold washington weather.

 

Same thing happened to me, brakes would start out fine, then get mushy with continued pressure. New brake master cylinder fixed it.

 

Awesome... looks like a project for tomorrow after a dentist appt.... bleck

 

brake fluid absorbs water over time. That is why your not supposed to leave a container of brake fluid or your master cylinder opened for any extended period of time. Water boils at 212 degrees. Brake fluid boils much higher depending on the type of fluid. Dot 4 generally boils higher than dot 3 fluids. This water in the brake lines boils and causes spongy braking. I forget exactly how it does this. I believe it creates like an air pocket in the line but im not 100% sure.

As for your problem bleed the brakes. Get a turkey baster or something and get all the black fluid out of your master cylinder. Fill it with new fluid. Bleed the brakes IN THE CORRECT SEQUENCE until you get fresh fluid while topping off the master cylinder. After your done, pump up the pedal see if you have a good pedal, check for any leaks. Then get back to us. That is the first thing I would always do if I had a spongy pedal.

 

but would that cause the systematic pressure, back off, loss of a little pressure, back off little less, etc... wouldn't it just be mushy down to the bottom of it was air?

 

master cyl is dead

 

Yup master cylinder did the trick, replaced it, bled the MC and brakes feel better than ever. Thanks guys!

 

I believe that the seals in the master cylinder going bad actually does exactly what you said, it will creep. However like i said before I always bleed first before throwing money at it - $5 for brake fluid or $$ for master cylinder. Im glad you got it though.

Did you bench bleed the MC before installation ?