Spongy Brakes!!

[gpk_gti]

Hey VWw'rs!

yesterday planted it to pass a guy on the left and he went to also change lanes on top of me,and as I slammed my brakes,the pedal instantly went all spongy! not all the way to the floor but,half way and did not have that caracteristic hard feel.

Made my heart jump as I thought the car would not stop.The ABS still activated.
This has happened once before a long time ago.Hard&sudden acceleration followed by a sudden stab of the brakes caused it.

Any ideas as where I should be looking??

[mikinoz]

Try this again in a controlled environment and see if double pumping, ie. depressing once, and then letting off, and pushing again helps.

I would suggest that if it is spongy, there may be air in the line, the questions are why?

Rear brake lines on MKIV are common point where the brake hose rubs against the body, however, I doubt this is the problem, because you still can stop.

[gpk_gti]

yeah actually mik after it happened I did try to recreate the same thing,but nothing! if there was air in the lines,wouldnt it happen more ofter?

now that I think of it,both occasions it happened whilst on a 1/2 left hand turn on the wheel whilst hard acceleration and sudden release of accelerator to stamp on the brakes hard...... its got me

[Jmac]

mate you are right about the air. If you had air they would always be spongy. How are they now mate when you use them normally?? Were you on them a fair bit before that??? Just trying to think of an answer, if the answer to the last question is yes then you might have been gettin some brake fade other wise its something else, possibly master cylinder. Ive changed a few of them. And there is a few tricks when you change it. If they are crap when normal then you will have to clamp the lines off 1 by 1. Let me know mate

[gpk_gti]

no mate,this definately did not feel like brake fade,it felt like I had no brakes,as the pedal went further down than normal.
brake fade feels like your compressing to normal position but nothing is happening.
I was not driving hard before this happened.

The last time this happened was about 1 yr ago and hasnt happened since.Master cylinder again would be happening more often?????

[SoVeReIgN]

I don't know much about brakes so take this with a huge grain of salt - Could you be a little low on fluid and the huge g forces when you're accelerating (mtm chip right? ) creating abit of a shortage of fluid where its needed (brake fluid surge??) ?

[gpk_gti]

fluid is at correct levels.thought of that one

[Jmac]

How are they normally mate?? You might have to clamp flexis off 1 by 1 to diagnose. Sound like a weird one but hey there is an answer for everything. Ill do some research mate.
Cheers

[gpk_gti]

hmmm,,,normally the work fine.although on high highway speeds and sudden braking you get some shuddering but id say the discs need replacing.have been putting that mod off.other than that,very good....