ilikebig928butts

I hope y'all shark lovers had an awesome Thanks Giving!

1) For a couple of months now, when I start her up in the morning, the 1st few brakes have gotten mushy. But after about 5 minutes or 1/2 mile of driving, the braking is normal. I dug through the forum for similar symptoms, but found nothing. Plenty of brake fluid...

2) My front wheels are always covered in brake dust whereas the rear is clean as heck. The four disk brakes are not all activated at the same time when I hit the brakes?

mark kibort

re bleed brakes or you have a master cyl issue.

mark kibort

you can jack up the rear of the car and see how much pedal it takes to stop the rear tires when you give it gas (rear of the car on jackstands) they are probably working just fine. fronts do all the work, so there is always more dust up front.

Mrmerlin

go for a drive use an IR gun and check the temps of the rotors write down the results.
From info posted , your MC is getting ready to go, time to be replaced.
the dusty wheels are a function of the brake pads.
Try fitting new pads that are know for making less dust .

NOTE factory pads make more dust BUT generally work better in all conditions.
less dusty pads may make more noise when cold but stop better when hot and make less dust.

ilikebig928butts

Thanks Mark and mrmerlin. I kinda came to that conclusion looking elsewhere about general mushy brakes... The master cylinders gonna hurt the wallet, especially around x-mas...
Are the PBR Deluxe cermic? The ones on 928intl.com just says "brake pads - low dust..."

dr bob

Before you get to replacing the master cylinder, consider that the ABS system does a little 'self-check' on cold start after the car has been sitting. I notice that the pedal drops a little in concert with a few ABS pump cycles. It's a Good Thing. Listen for a few telltale clicks/whirs on first forward brake application and see if the noises and the lower pedal coincide.

I run the pads that 928 sells/recommends for street use. They are extremely low dust especially compared with originals, and do a fine job for my (conservative) driving style.


For rears doing less than their share of the work, the temperature diagnosis recommended here by others is good. If the rears are doing nothing you'll want to figure out why. Rears doing less can be caused by a few things. Prominent is the habit of 'saving money' and only replacing the front pads that are worn more. Replace full sets of pads, and let the new rears do more of the work. Additionally, Porsche was, um, sensitive to the issues of oversteer under braking, limiting the rear brake system load a lot using a rear pressure limiting/proportioning device commonly referred to as a 'bias valve'. Unless you are driving in snow/ice conditions with failed ABS, most folks here will suggest that you can go at least one step higher on that bias valve so the rears can help more. A little searching will add to this guidance, and your favorite parts vendor can help you get the right valve. Good time to do it now since you are flushing/bleeding the system anyway.

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Master cylinders will last forever if the fluid inside is kept clean and dry. The normal fluid replacement interval is two years for street-only cars. I live in a very dry climate, and replace the fluid more frequently. Folks that track their cars know that tech for most sanctioning groups requires fluid less than six months old, and they sometimes end up changing the fluid at the track after aggressive driving/abusive braking anyway. For a street car, use good DOT-4 fluid, flush regularly, and a whole lot of corrosion-related hydraulic issues won't appear. Before you replace a suspect master cylinder, flush the old fluid out of the system carefully, and see if some problems go away with the old damp/dirty fluid.

mark kibort

I did some pretty interesting testing of the effectiveness of the rear brakes. In the end, by calculation and empirical testing, I found that the lowered rear brake bias is very beneficial to racers. I went up a bias setting and found trail braking would lock up the rears and put the car into a slide. changed it back to stock and that problem went away.. I use way way less pads in the rear. this is because, when you are threashold braking, most all the braking force is up front. only a few hundred lbs is sitting on the rear tires, and that means the potential for the rear brakes to add much is pretty diminished. now, crusing around, is a better case for more rear brake bias as you can share more of the braking load and make the fronts last longer, but when you want sheer performance, you don't want much rear brakes...... plus, you get a lot out of engine braking as well!

stuartbrs

The brake pedal on my S4 does exactly as you describe. The first application when cold feels soft, after that it feels normal. I thought it might be the master cylinder as well but its been like that since I got the car 12 months ago. I have replaced the fluid and it does the same thing.