Brake Booster vs Brake Master Cyl problems: super soft pedal...sometimes
 

This problem started today and it is very annoying/dangerous.

Sometimes the brake pedal will go all the down to the floor to start braking. I have to give it one or two pumps to get back to normal brake pressure. It has done it at least 10 times today on two different trips.

The brake fluid level is fine, I do not think there is air in the line; but it still is a possibility.

Now, if anyone else has had similar symptoms, what did you check/replace?

does the temp of the brakes change the pedal pressure(starts right away or after a couple of good stops)?

your sure the level hasn't gone down at all?

How old is the current fluid have you boiled it/used the brake very hard recently?

after its back to reg pressure is it firm or does it still feel weak and then sink?

Hot or cold it doesnt matter. The fluid cannot be more than a year old. I have not done any high speed braking, just normal city driving.

It can happen as soon as I start the car or when I am pulling back in to park.

I will be gone this weekend so I will bleed the brakes next week and see how it reacts.

im leaning towards master cylinder or small leak although i have never personally experienced a bad brake booster most times it would mean firm pedal not weak unless it leaks past the seals then you would see missing fluid.

Ya now im leaning towards not flushing the system incase it is the master cyl then i will just double my work.

Yea good point. Your fluid getting darker ? A lot if times a small leak in the seals at the master cylinder will leak into the fire wall you won't see the leak but it can cause the fluid to get dirty quicker just a theory happened to my bro but it was his slave cylinder not master should be the same tho

classic signs of a failed master cylinder. the o-rings around the piston fail and fluid leaks by, giving you a spongy pedal... but you see little or no fluid loss.

Signs of a bad booster are rock hard pedal and/or bad engine idle if the vacuum side is damaged and leaking air back intot he engine through the brake booster hose. so that's most likely not your problem.

To check the MC, it away from the brake booster (just undo the two bolts holding it on) and see if any fluid leaks out between them. if so, then the MC is definitely done.

be sure to follow the bench-bleed instructions on the new master cylinder. If you don't, life will not be fun installing the new one.

also be sure to check all of your calipers for a fluid leak. I doubt that's your issue, but if a piston seal has gone bad, you can usually see the signs of fluid leakage pretty easily.

Sweet, thanks buddy. I'll check it out on monday when I get home.

ugh this is happening to me. there was a fluid leak in one of the calipers and that got fixed...now the pedal STILL goes all the way to the floor and barely stops the car. so it must be the master cylinder?

could be a bad bleed.... re-bleed the system

lol i'll have to bring it to another mechanic to do that...but how can it be a bad bleed...because there's air? and if it was the master cyl how would i know?

soft pedal
 

Newbie here, but i think i may have a solution, Had same problem in my 4th gen, checked MC and there were no leaks. Iimedetly changed all four rotors and brakes (not to much expense), Our shop we have i used our power bleeder, got all air out of lines while bleeding with machine, pumped brakes 3-4 times then to floor open bleeders, repeat untill you see results. My pedal was good as new after all this. Just dont rule out the simple things.:idea:

Just and average joes opinion. Hope this helps

Air in even one caliper line will cause a soft pedal. They have to be bled in order - from farthest (pass rear) to nearest (drivers front). Without a air pressure power bleeder kit really takes two people to do it right - one to pump/hold pedal and one to open/close bleeder valves. If after all that you still have a problem, then look for leak in master cylinder.

I had the same problem just about a week ago. I replaced the master cylinder and it was all good. I put new fluid in and bleed the lines and i was all good. The way I know if the booster is bad is if you would here like air coming out of a tire real fast inside your car. I had that problem.

I also need a little help. I'll try to give as much info as I can, sorry if it's too much.

A couple of months ago I changed the front pads & rotors and had difficulty bleeding the front but finally got it done. Didn't touch the rear. Brakes have been engaging at a lower level on the pedal since then. Just got new tires and they said rust is on my rear rotors, so their not working.

I am trying to bleed RR but can only get 2-3 inches of fluid to enter tube no matter how much I try to bleed them. With the car off I thought I'd try to gravity bleed, but it sounded like air then entered when I opened the valve.

Not knowing much about brakes, I'd appreciate any help.
Thanks.

does your ebrake work? it sounds like the calipers are shot you most likley need to replace em

Yes the ebrake works

If you have abs brakes, you need to get the brakes bled properly.

No, I don't have ABS.

It seems odd to me that I got some fluid out but not much would flow. Not knowing what the symptoms of each component, is it most likely my calipers, master cylinder, brake booster or something else. I have two calipers on the way to me from Rock Auto & hoping that cures it.

Rear calipers need replaced. grease the pins as well. There is no need to bleed when replacing pads and rotors. Bleeding is only necessary when you disconnect a line and introduce air, otherwise leave it unless you want fresh fluid.

The pedal seemed spongie after I had to compress the caliper to put the new pads on.

So what was wrong?

So what was the problem?

Changed the MC and prob didnt come back...