Brakes spongy when engine running yet fine with engine off..

[MercuryFree]

Hey all,

I've managed to fail a warrant for my brakes being too spongy, even though they perform just as well as they should. Conventional wisdom would suggest air in the lines, so I bled them with new fluid but did not help (have now bled lines three times, twice with car off once with it on (but not engine running) ).

The brakes work 100% fine, and are hard as a rock when pressed with the car off, but are 'spongy' up to about half duration of the brake pedal, tightening up after this.

Any advice? Google reveals many people with the same problem, but no hard solutions anywhere. My brake system does not 'lose' fluid.

Oh, car is a 1996 SS3 Celica, 4 disc w/ ABS.

Any help would be 1000 times appreciated

[gasman]

could try replacing your rubber lines with new ones if they are a bit old. ore even better got for some braded ones

[tsoob]

yeah sounds like u got a leak some where could be vac or hydraulic check both

[lucasthefallen]

pump it up with the motor off so it goes rock hard. hold the pedal down hard while starting the motor. if it slowly sinks to the floor thats normally a good sign that the booster is ok.

[postfach]

something wrong with the booster perhaps?

[matt dunn]

something wrong with the booster perhaps?

or perhaps there may be nothing wrong with it at all.

How spongy is spongy?

How does it compare to other toyota's for pedal feel?

[fivebob]

something wrong with the booster perhaps?

Not from the symptoms described, more likely a worn out master cylinder.

[MAGN1T]

Well it's not a mitsi, but with a mitsi and ABS you bleed the brakes with the motor running.
Otherwise they stay spongey.

Steve

[pc]

something wrong with the booster perhaps?

Not from the symptoms described, more likely a worn out master cylinder.

Sounds likely... with the engine running the booster is working as well and that might be enough pressure to have the master cylinder leak. (leaking internally).

[MercuryFree]

pump it up with the motor off so it goes rock hard. hold the pedal down hard while starting the motor. if it slowly sinks to the floor thats normally a good sign that the booster is ok.

OK just tried that, it sunk slowly to the floor in a non-broken feeling manner, so that's a plus (looked up how much boosters cost to replace, ooooouch)

something wrong with the booster perhaps?

or perhaps there may be nothing wrong with it at all.

How spongy is spongy?

How does it compare to other toyota's for pedal feel?

I've never driven another toyota, amusingly enough...but it's spongier than any of the other cars (around 5-6) I've driven that I can recall. I don't even remember it getting spongy, so I assume this problem has crept up over a few days or weeks at some point so that I was used to it

something wrong with the booster perhaps?

Not from the symptoms described, more likely a worn out master cylinder.

Will try and get toyota or brake shop to check it out tomorrow I guess, master cylinders aren't that cheap to replace I imagine? Sigh. This car has been on the whole worry free and this current warrant has run me $900 so far and counting...sigh.

Thanks for the help guys (although if anyone has anything else feel free to speak up )

[Lloyd]

Could be a picky WoF place too, Prado brakes and the like feel a little bit like something is wrong if you're not used to them too. If you can pump it up so its hard, leave it off for a moment and then reapply pressure and its no lower then chances are they're fine

[iOnic]

How old is your brake fluid?

[MercuryFree]

How old is your brake fluid?

It was probably old enough to need changing anyway, not sure as to the exact age, but having bled them three times now there shouldn't be much if any of the old stuff left in there I'm thinking?

[iOnic]

Nah if you're bled it that much most of that crap will be gone. Was just thinking the fluid may have been saturated with water which was causing vapor locks and the spongy feeling in the pedal (didn't really read the thread fully so I may have missed something)

[Snaps]

I get the same thing in m supra, brakes go rock hard with the enigne off, with the engine on they feel spongey. Though they felt less spongey after swapping the brake lines for braided.

I think it's normal.

[®usty]

didn't you change your brake pads a while or something? bleed them properly??

[rollaholic]

if you put your foot on the brake with moderate pressure while the car is running and the pedal gradually sinks down to half travel or lower then i would be looking at a master cylinder. the seals wear and fluid is able to bypass them which can cause this symptom.

they arent super expensive, around 150 retail for something from repco or similar

if you do decide to replace it, it needs to be bled in a vice or something before you install it - may pay to have someone who knows what they are doing handy (if you dont that is)

[Flannelman]

had this issue in my old falcon, had the master cylinder honed and rekitted, brake pedal is awsome. no more half pedal before brakes work

be cheaper to replace the master cylinder than to rekit, cost me $180 for the work done

[Dell'Orto]

Now I'm having this issue too AE101 20v Non ABS. However in my case I'd just removed the engine to do various bits and pieces, and have replaced all the brake lines/rotors/pads etc. I've bled the brakes up a couple of times now and no air comes out at all, with the car off the pedal is perfect but as soon as you turn the car on the pedal turns to mush.
Before taking it off the road to do this the brake pedal was fine. Also should mention that when you pump the, the revs rise ~1000rpm

[B_giB]

Had same problem in my 101, bleed the hell out of it, did nothing. Turns out my pads where that low

Replaced pads, Mint again