Help please: softening brake pedal on 996T?

Hi all, just took a punt on a cheap 996T and am slowly identifying all the niggles. Next one up is the brake pedal, which starts off firm to press, but then very gently gives way as you hold it (car is a tip, so you hold it still on idle using the brake) almost like the brake fluid is just starting to boil. There's no way the brake fluid can be boiling, unless it's mainly water by now - the car has barely been driven for a fews years and I suspect it has t been changed for a long while. The brake fluid level was also low enough to trigger a warning on the way home from the dealers. I've since topped it off, which has cleared the warning, but the brake pedal giving way is still there. Brakes still function well. Does anyone gave any ideas on what the issue might be please?

Sure it's not your ABS malfunctioning and the pedal is slightly pulsating and dropping whilst it does it?

Easily diagnosed by pulling the ABS fuse out and seeing if it stops.

It's a buggered master cylinder. The seals are slowly letting fluid past when constant pressure is on the pedal. I bet if you hit the pedal quickly and hard it's intitually firm.

Correct. :thumb: It feels firm at first, but then it does feel like that pressure "leaks" away. So, is this a big/expensive job to replace? No pulsing, by the way Alex. It's a slow and steady release of pressure from firm to soft. Though thanks for the tip.

How do the brakes actually work / stop? I thought mine was a bit spongey and mentioned it to the indy when in for service and he said they're fine and got me to jump in another car and try it and they were the same. I'd try bleeding them first though the nipples can be a bit of a problem!!

Thanks! They initially feel nice and firm on the initial press and stop the car well. It's only when you hold them on that you can feel the pedal sink. The initial feel on pressing is much better/firmer than on my old 996 C2, which I agree feels overly spongy.

I changed my front brake pads and it totally transformed what the feel/pedal travel was like. Ps. Don't forget (sorry if this is really common knowledge) - the calipers have 2 nipples (like a beautiful woman). The front one and the one hidden behind the disc. :thumb:

Can i humbly suggest you stick your head under the car starting at the n/s center and look for a leak .. it certainly sounds like you have one to me .. Low fluid and a traveling pedal !!

Will do! And you don't need to be humble about it - if you wrote "Just stick yer head under it you *****' idiot and see if its leaking" I'd gladly take your advice! :thumb:

Could well be, I was assuming (perhaps incorrectly) a leak had been ruled out.

Ding ding ding! First prize goes to deMort! :thumb: Can't get under the car just yet but took a look at the reservoir and it's less than half full! And I filled it to max 3 days ago! It took another 250ml tonight just to get to the min line. No sign of a leak in the frunk, will have to get it on a ramp. Are these cars prone to leaking brake fluid in any particulararea?

There is a clue though from which end of the reservoir is empty. MC

I don't know if you know but the reservoir has two halves seperated by a weir. Each half supplies fluid to one of the two circuits. If one of the circuits has a leak the weir stops you from losing all the fluid so one circuit stays working. In your pic one side has no fluid at all so it must be a reasonable sized leak which also means it will be easy to find. Just thought one place you can have a leak which is not so obvious is from the rear of the master cylinder so it'd be worth checking there also Mac

Did you check the MOT history, any advisories for corroded brake lines? Given my experience corrosion in the steel lines is likely. Steve