Mr.Alex

Here are some bullet points to sum things up.

1] Friend clips curb, sway bar taps booster and over time the pedal grew heavier and heavier.

2] Find a vacuum booster on pelican and buy it, after swapping it the pedal goes almost to the floor with brakes grabbing strongly close to the bottom. The pedal doesn't spring back as naturally as the clutch or as the older booster.

3] Buy a refurbished master cylinder, as shop suggests that the booster was masking the issues of the master cylinder having failed as well. But after swapping the pedal is pretty much exactly the same, but people tell me that these refurbished units sometimes come out bad out of the box.

4] A fellow member lends me his 964 master cylinder [forever grateful] after having gone the 993 route to troubleshoot my refurbished cylinder, but after swapping the pedal is exactly the same as with my old master.

The tricky thing is that usually a bad booster will always give a hard pedal, but could it be possible that it is indeed giving me the soft pedal? I always assumed it was the master, but after trying two different master cylinders, I go back to the thought of the brakes only getting like this after putting this booster in.

Possible the return spring on the booster is the cuplrit?

Here is a video of the pedal travel and snap back.

Rocket Rob

I've swapped out my booster and master cylinder for used good ones and am not happy with the result. The pedal travel is long, even though I have bled the brakes twice. I will be curious to hear what others have to say.

As for the slowness of the brake pedal, I will have to pay attention to it. Maybe mine is doing the same.

Mr.Alex

Interesting to hear, in theory I thought buying a used vacuum booster is not a big deal since its relatively simple thing with no hydraulics or anything. Ive bled the **** out of these brakes, so many times I have dreams about it.

But let me know how your pedal behaves. I drove FlyingTomatoes car over the weekend and the brake is firm right from the get go, and relatively little pedal travel in general.

Whats kind of bugging me is that my pedal is almost equally soft with the car off as with the car on. Perhaps the check valve?

h100vw

Hi, No expert on Porsche brakes but I have some experience of brakes in general which may help. I run a few VWs neither of which are available in the States.
However, having done some caliper upgrades on them the brakes never really felt sharp and certainly the bite was missing. I heard of a guy on a forum that was having trouble bleeding the some kind of car. He was trying to run the ABS pump believing that there was air trapped inside.
You guys may have heard of Ross-Tech VCDS diagnostic cables. I have one and while poking around in the ABS controller. I found that there was an Output Test facility.
So I ran this, essentially you just follow the prompts it gives you. It allows you to pick bad valves in the ABS. You might hold the pedal and the controller releases the brakes on each corner individually, as you progress through the test.
Now I am wondering that after having broken into the system a few times if air has got into the ABS block and if there's a Porsche way of doing the same thing.
My brakes improved massively and now feel showroom std again on a car that's got touching 200000km on it.
Gavin

ThomasC2

And me to! Same problem as Rocket Bob. Bought second hand 993 parts. Bled my system 3 times but pedal travel is long with a soft bottom. But the pedal itself feels ok, not slow etc. It works good enough to engage ABS and I did a trackday and it didn't get worse. But as it works it is now worse than my old 964 cylinder.

Can a master cylinder be "semi-bad"? I thought they went totally bad when they became bad. The cylinder I bought had been lying in a box for some years but it was sealed and not dry inside . So next step? By a new master?

JasonAndreas

C2? When you replaced the brake master cylinder did you follow the workshop manual C2 addendum instructions for bleeding the quickfill port? (blue arrow below)

ThomasC2

Do you mean me Jason? I have put on 993 parts so there is no bleed valve on these cylinders as on the 964 cylinder.

Rocket Rob

Yes, I bled at the master cylinder too. Did I look at the C2 section? No. Drats.

Mr.Alex

I honestly never expected to hear some of the same soft pedal stories, especially from Thomas being on the 993 parts, which I figured could be my next move if nothing gets sorted. In regards to Jason, I bled the master several times with power bleeder, and both nipples on the calipers.

For you guys, how is your pedal when the car is off? Currenty mine is a bit stiffer but has some travel and doesn't get rock hard, I also really can't 'pump up' the pedal. I'm not sure if its my sanity slipping, but I think while driving I had a decent pedal today, although after coming to a stop the pedal would kind of get soft at idle. When I get back I'l quickly try a dry bleed with the master to see if I can get anymore air out and firm the pedal up, but if not I'l have to remove this master and return back to the rennlister who loaned it to me.

ThomasC2

With the engine of my pedal used to be (my old 964 cylinder) almost solid with very little travel. Now it doesn't get as stiff and the travel is longer. So there's a clear difference with both engine on and off.

So it seems that my used 993 cylinder isn't working as it should. A learning is probably that you shouldn't buy used parts when it comes to parts like brake/clutch cylinders. I know that the one I bought had been lying around for a couple of years, all though not dry inside.

I'll order a new one today.

Rocket Rob

FYI - I just read through the C2 bleeding procedure that Jason referred to. It states that you should open the bleed nipple on the master cylinder and aggressively pump the brake pedal being sure that it returns fully and to fully depress each stroke.

This is a step I haven't taken. I will try it this coming weekend. I am curious if anyone else that is having problems has skipped this step too?

Jason - Thanks for the idea.

JasonAndreas

Definitely let us know how it goes. The C2 ABS is really simple. You either have air in the system or a failing pressure seal? What else could it be? That said, I have an extra ABS pump (I know you replaced yours...) and I just bought a Bosch ABS 2-Led tester (should be here by the end of the week). And Nashua is only 1.5hrs from Providence driving the speed limit.

Rocket Rob

Everyone - Saturday, my friend and I re-bled the brakes using the workshop C2 addendum. No change, so we swapped in the original master and then bled again. It took a lot - maybe 10-15 cycles. The air came out in tiny bubbles. It felt like it would never improve but then suddenly, the pedal became hard and the bubbles stopped. yippee! I took it for a test drive this morning. The brake pedal is nice and firm and the pedal travel is back to normal.

In hindsight, I suspect that the used master cylinder that I had installed is probably fine and we just didn't bleed all of the air out of it.

Mr.Alex - I can't explain the slowness of your pedal return but definitely recommend re-bleeding your master.

Jason - Thanks for the recommendation on the C2 addendum.

ThomasC2

sound good! I picked up my new 993 cylinder yesterday and will install it tonight. I'll be back with a report!

ThomasC2

OK, installed my new 993 cylinder yesterday and did two rounds of bleeding with my Motive bleeder. And it is much better. The "drag" feels better and the bottom is harder. I'm not yet 100% happy though. I think the travel should be a little shorter and also a bit harder at the bottom. But when I fill up the system and go around bleeding the fluid gets a lot of air into it in the process. So I'll let the car stand until Thursday and (will be away from home tonight) and then do I final round of bleeding when the air probably have settled in bigger bubbles.

But I can say that a bad cylinder was my problem. The feeling is already different even though it's not 100% yet.