911 Master Cly
Stock lines
1987 front end incl brakes
SC rear rotors and calipers and ebrakes

ebrakes not functioning yet. (this doesnt seem to be the issue)

Symptom:

Brakes fluffy at first, after 3-4 stops from 50mph they are very good.

After 10-20 stops the pedal is like a rock. Almost seems like they are gripping even when pedal is all the way up.

What could be going on?

IMHO, if your brakes are "fluffy" at first, and then with use they become hard I would say air in the system. Bleed them and the P-valve with extreme pregudice.

That is with out dealing with "seems likes".

Indeed another round of bleeding is in order.

What of the other issue? I cant imagine the rotors thermally expanding so much that they drag in just 4 or 5 miles of driving?

Nor I, but they do drag by design. Dr Shea... Calling Dr Shea.

I'm having trouble bleeding a new system - getting the pedal up and not spongy. I wasn't aware there was a proportioning valve to be bled - does it exist in a 1970-4? If so could you tell me how to bleed it?
New 19mm master, new 911 front rotors/pads & rebuilt calibers - rears untouched.
Thanks,

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It is inline on the firewall, when you bleed the rears it will get done.

I have only bleed mine two times, most people are telling me three or four times minimum.

That really wasnt what I was asking though...

Mine was more of why are they closing up when hot...

Because when the air gets hot it expands.
and with air in the lines the pistons can have trouble returning to the released state.

AH!

Excellent Explaination!!!!

One other thing to check is the actuator rod that presses in on the master cylinder. If the rod is mis-adjusted (too long) then the brakes will never fully release and continue getting tighter and tighter. After the brakes cool for some time, everything starts over again.

Make sure that there is a gap between the end of the brake pedal rod and the master cylinder plunger (1mm should be sufficient). You can pull up on the brake pedal slightly to feel for the gap.

Good luck with it.

Get your windshield trim installed?

how do i check that? cant see it from underneath the car. not even sure I can see it with the pedal board out of the way...

perhaps moving the brake pedal when stone cold to feel for resistance...

nope, chrome trim still held in place with duct tape.

Air in the line is the problem.

RE: Bleeding the P-Valve for Tyler - I generally don't. I like to get the system bled and operating and then take the car for a few "spirited" drives. Some vacant parking lot stops (agressive ones) and some average road bumps usually get the P-valve to burp out any excess air.

After a few days or weeks, go back and rebleed the rears. And, yes, your car has one... they all do (did).

E.

The way I check that is to remove the pedal board and unscrew the jam nut and (with my fingers) run the actuator rod down until you feel it contact the piston and then back it off part of a turn and then tighten the jam nut.

I only suggest checking this as you had your entire car apart recently.

Once adjusted and tightened down, it will never require any future adjustments unless the master cylinder is replaced.

Air is a possibility, but I never heard of air giving a nice solid pedal. Since all air that I know of compresses, I would still expect a squishy pedal.

As fluid heats up, it typically will expand.

You could also have a brake pad dragging.

By all means, rebleed your brakes.

When you rebuilt our calipers did you clean the pistons real good?
That dried fluid rust crap will raise hell with the retracting of pistons and pads. also the two pins in the caliper will cause things to bind up.