micah_m

My brakes are very spongy... They don't really grab much till the pedal is almost to the floor. I noticed it after it had sat for about a week without being driven. It wasn't a gradual fade, they worked fine then after it sat for a week the pedal was really soft.

What should I check? Also thought I'd add that pumping the brakes does nothing when I am driving, but if it is shut off pumping the brakes a few times builds the brake pressure back up.

S!K TEG

how are you on brake fluid?

lostforawhile

you have a leak somewhere and air is getting in your system, thats what makes the pedal seem spongy, time to inspect your entire system, if you can't find anything else, could be an internal master cylinder leak

micah_m

My brake fluid is really low, but the problem is that I don't see where it's leaking. Would adding brake fluid then checking around for leaks after driving it be a bad idea? I just don't want it to get on and mess up my paint if it leaks more.

Also I forgot to add that the red brake light on my dash is lit up.

lostforawhile

if it's gotten so low that there is now air in the master cylinder, you are going to have to remove the master and bench bleed it, and why have you been driving around with your brake light on? that means you have a serious issue going on and shouldnt be driving anywhere

micah_m

I'm not driving it now, my prelude isn't my daily and I don't drive it much. Also I didn't realize until the light stayed on that it means there's a problem with my brakes. I thought this light was only to show that my ebrake is up... Didn't know preludes have a light for brake problems.

Is there a chance that topping off the brake fluid would help with my problem? Or do I for sure need to remove the master cylinder?

lostforawhile

the brake warning light in almost all cars indicates either the brake fluid has fallen to a dangerous level, or the E brake is on. If the fluid in the master cylinder has fallen to a level where the fluid inlet ports have been exposed, then, yes it needs to come off to be bench bled. There are a lot of good videos on youtube that will show you exactly how to do this, the reason it has to come off, is the pushrod in the booster,can't push the piston in the master far enough to bleed out the air bubbles. It's not difficult to do, but takes some time. you get a kit with some plastic nipples that screw into the ports on the side of the master, then you run rubber hoses back into the resevoir, you need something to push the piston all the way in, until all the air bubbles are gone. You need to find out the source of the leaking fluid, if it's dropped that low, it's gone somewhere. You may pull off the master, and find the rear piston seal is blown, causing fluid to leak out the rear of the master.

micah_m

Makes sense, I'll definitely be doing this very soon. I'm just surprised I am not seeing any obvious leaks anywhere. Master cylinders aren't too expensive, so I might just buy a new one and replace it even if it's not what is causing the leak, since it already has to come off to bench bleed it. Thanks for the detailed response, I appreciate it.