spongy brakes.....think it's the master cylinder
 

I got my brakes done awhile back and we got most of the air so that they were fine, but I also figured out that I had a small leak i think in the master cylinder because I would be losing a very small amount of brake fluid and have to fill it up every week or so. Well, I go out to get in my car today after not driving it for 4 days (vacation) and the brakes go all the way to the floor. I put more fluid and they got a little bit better (drivable), but not by much. Any suggestion? I think it's the master cylinder because I can here a little air coming out when the brakes are applied....... :squint:

Have you tried bleeding the brakes?

I think you are correct in presuming it is the master.
it's the only part in the system that can leak without being able to see the leak.

how much does replaceing the master cylinder cost - in terms of time, parts, and beer. I think I've got the same issue

I heard it's not too hard

Replacing master cylinder is quite easy..cost...$50 with core.......you must bench bleed the cylinder before installing it on your car..I replaced mine last month because it was leaking brake fluid out between the cylinder and the booster drum..that is where yours is prob leaking also..you can replace it yourself in about 45 minutes. Make sure you have break line flare wrench 11mm to remove the break lines.

get in the car and without starting it ("ON")... pump up the brakes... if the pedal gets very hard and u can't really push anymore then your problem lies else where, not the mc....
i think thats how it works.. well try it anyway... if the pedal still feels soft then its the booster or the mc.

It's the master cylinder. Not hard to replace. Take your time bleeding the brakes though. Autozone repair in the stickies

Is the master cylinder and the core the samething?

core is what they charge to make sure they get the old part back

when you buy something rebuildable like this, they make you return the original aka "core" so that they can take it, fix it and resell it

if you dont give yours back, they get you with a core charge which sometimes is 50% or so of the price for a new one

I would honestly just buy a new mc. I put a rebuilt one from autozone in and it was broken :(. The bmc is one of the most important pieces on the car, why would you wanna risk your safety putting on a part that has already failed in the past?

yeah, but the difference in price is major.
you're lucky to have people on this board buy new $50 parts muchless $90 parts
I do have brand new ones available if anyone is interested.

thats where we saw it leaking ...tween the m.c and booster

also you can avoid bench bleeding. install as usual but before bleeding
indivdual lines pump the brake pedal about half way down rapidly in short
strokes check fluid level and repeat.

Really??? I thought that would just put air from the cylinder into the lines.Only takes 10 min to bench bleed and is very easy. :chairshot

True only if you fully depress the pedal but using short strokes the bubbles come up into the resovoir

thanks..Good tip..I will try next time

I got the tip a few years ago from an old gearhead I've done it since, it does save a little time

Or just leaving it down all the way sometimes does it.