80 sc brake problems
 

I just finished rebuilding all four brake calipers. There was a lot of dried gunk on the caliper pistons.
Got everything cleaned up and reassemblied. The problem is soft brake pedal. I seemed to get all air out but the pedal still goes to the floor. When it reaches the bottom of travel, I can't spin the rotors. Seems like good braking. What else could it be? How do I check the brake booster master cyl. to make sure no problem there?Thanks.

How many times did you bleed the system? How did you bleed it? It can take several bleedings to get a good pedal.

Also, drive the car around if you feel the brakes work well enough to be safe. Bleed it again after you put some miles on it.

Did you push the brake pedal all the way to the floor while the pads were out? If so, you may have pushed the piston past the seals, which can cause an internal leak.

http://forums.pelicanparts.com/porsche-911-technical-forum/566702-master-cylinder-question.html

It takes a while, couple hundred cycles of the peddle, to move the pads closer to the rotors, just sit in the car and cycle it. But do make sure no air is in the system. See the write up in the Bentley manual about the piston seals.....And tell the next guy about your ordeal when they ask the same thing-pass it on, pay it forward.

Does it matter if the engine is running while you do this? (vacuum booster involvement). I assume not but thought I'd ask.

Also, I think Early S Man had some good posts on getting the pads snugged up to the rotors right from the start. A search ought to bring them up.

Passing on my recent experience on & 'paying it forward'...James is right (as usual :)).

I rebuilt my front calipers and replaced all the brake lines last fall, and bled 5 times around the car, and still had a little bit of a soft pedal, but with several drives and some spirited braking, they feel alot better now.

I replaced all the seals in all the calipers, reassembled and reattached to car. I will try to rebleed all four corners several times as pointed out be forum members. Thanks for the help

James is right. Don't worry about re-bleeding right now.

1. Did you bed your pads?

If not, do so. If they're old pads, you can always do it again. The issue you are having is (probably) due in whole to the new seals in your calipers. They are pulling your pistons and hence your pads off the rotor. The heat cycling of the calipers in the bedding procedure will help brake in the seals. This is what happened to Dave above when he mentions the pedal came up after some spirited braking sessions.

Here's a bedding procedure we recommend for our customers:

911 Tech Tips

Hope that helps.

Great feedback guys, sometimes it hard to explain this about the brakes in a Porsche. Most Chevy/Ford/Toyota guys can't get it. Now you know so the next new guy who asks this question (and there will), you tell them! Thanks..

i bet you still have air in the system. trying to spin a rotor by hand is no indication that the brakes are grabbing.

you do have the calipers in the correct place right..left to left, right to right? bleeder nipples are on top?

Air - Possibly but, this is very common with new calipers and new seals. Based upon where he is now (from his description), I'd venture to say the calipers are on properly.

calipers are in right positions, nipples are up. Today I will try to rebleed. I guess with rebuild, a lot more air in system. Thanks

I just replaced my master cylinder and I went around 4 times and still had a squishy pedal. I was using a power bleeder. I pedal bled and got a lot of air out. Went around twice and now have a good pedal.