mayday1

This is on a 99 C2 with 90K miles. I only drive the car for weekend autox, no daily use.

A few weeks ago the "brake wear" warning light came on, but would go away if I turn off the ignition and restart, but the light would come back on after a dozen miles or so.
Brake fluid reservoir is full, front pads have about 7-8mm left, rear pads have about 4-5mm left. So I ordered all new pads as well as rotors since the rotors looked visibly worn.

This past weekend, after a 60mile drive on the highway, the brakes were dragging after a stop,
I stalled the car a few times as a result. But the car tracked straight so both sides must be dragging the same amount. I noticed the driver front and passenger rear wheels seemed hotter than normal.
The dragging was intermittent and I autoxed the whole day with the drag coming and going. When the drag happens, the brake pedal felt much harder, as if I already pressed the brakes.

When I got home I pulled the driver front caliper off and noticed that it was extremely difficult to retract the pistons, as if the brake fluid cannot flow back to the master cylinder. Pushing in one piston caused the
neighbouring piston to come out, but the pistons on the other side of the calipers didn't move. Is this normal? Last night I pulled the right front caliper out and it had the same problem. The only way I could retract the
pistons was to open the bleeder valves. The fluid came out nice and clean, I don't know how old it was but certainly older than 2 yrs since that's how long I've had the car.
After putting in new pads and rotors in the front, and make sure the wheels were rotating freely (piston retracted), I pumped the brake paddle a few times, and
both front wheels have significant drag, I could rotate them by hand but they certainly wouldn't spin freely.

I haven't touched the rear brakes yet, will do so this weekend. Question: What is the likely problem?

DBJoe996

Time for a caliper rebuild with new seals and pistons. The pistons are probably corroded in the calipers and not retracting.

mayday1

I was hoping for something simple like that (piston rebuild). But when I loosen the bleeder nipples, the pistons can retract very easily, that leads me to think
the problem is not the calipers but upstream, may be the ABS or the master cylinder. I need a way to diagnose the problem.

DBJoe996

It could be the master cylinder, but I don't know a way to test it without removal and operating the master cylinder piston to see if it springs back smoothly. Doubt it is the ABS system.

Mike Murphy

Nein_11

I would also inspect the brake lines themselves. Age and general road wear can cause brake line deterioration. I have seen rubber and plastic lines collapse in on themselves due to age, preventing fluid from flowing freely in and out of the caliper (dragging or freezing the caliper at times). I haven't had this issue on any P car I have owned, but it happened to me on two other higher milage daily drivers I have owned.

Ahsai

Could be water intrusion into the brake booster. There's a TSB for '99 if you search.

Noz1974

It could be the pistons just corroded around the top edge and as you have new pads it pushes the pistons right in to the corroded part otherwise it may be you have a problem with fluid bleeding back into the system. If you go onto design911 then click full website at the bottom, on the left of the main screen it says parts diagrams, then go brakes then you get exploded diagrams for each area of brakes, you can have a look at things, I use it a lot just to see what I'm dealing with. Also I did notice when you click on disc brake front axle to go into the diagram underneath you get a full parts list with part numbers and prices, very useful!!! There is a brake booster modification kit listed at the top of the list, could this be your answer??
Good Luck

Noz1974

Sorry the kit is listed under the master cylinder diagram so click that then go down to the list!

JB001

As said Nein_11 you should take a look at your brake lines. The rubber hoses are 19 year old and should be replaced whatever.
There is a video on YouTube describing a problem similar to yours, fixed by replacing the rubber hoses.

$80 for 4 Ebay: https://www.ebay.com/itm/Porsche-911-Boxster-ATE-OEM-Set-of-4-Brake-Hydraulic-Hoses-for-Front-Rear-Side/361205950163?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Good luck

mayday1

With the car sitting cold for a few days, the rear brakes are stopping and releasing properly when the brake pedal is pressed and released. The front brakes are both sticky and not quite releasing (this is with new pads and rotors, but it was like that
with old rotors and old pads). So I suspect the front brake rubber hoses are bad. The rear brake hoses dont have a metal spring outer jacket, is that normal, or an indication that they were replaced in the past and can explain why they seem OK.

Now I have an additional problem of having two broken shims embedded in the top pistons of the rear caliper, I need to figure out how to remove them without removing the pistons.

I´ll update more as I work on it more.

Thanks to everyoneś suggestion so far.

mayday1

After replacing all the brake pads and rotors, as well as the front brake hoses, the problem remains. It seems like the brakes dont drag when cold, and drag more
as the brakes get hotter. When I parked the carwith the brakes dragging, the drag goes away after a few hours of cooling, only to come back after a few miles
of city driving.

Whatś next? I´ll need to bring a jack with me on a drive, wait till the are nice and hot and dragging, then jack up the car to tell which brake is dragging, and
repeat a couple times to see it is always the same wheel(s).

fpb111

mayday1

pentosin dot 4.

Today I played around some more with the brakes. they definitely don't drag when cold, and drag when hot. When the brakes are dragging, I pulled into my driveway (very slightly sloped up),
and the car rolled back a few inches as I was getting out, that was enough to un-seize the calipers and all the wheels where rotating freely. Then I pumped the brakes couple of times, and the rears were
rotating quite freely with a tiny amount of drag, but the front were hard to rotate. Wait for half an hour or so and the fronts were freely rotating again.

Any ideas?

Porschetech3

Brake fluid absorbs moisture like crazy. Old brake systems on domestic cars had cast iron master cylinders and sealed reservoirs and were less likely to absorb moisture, hence could go longer without service. Modern brake systems have aluminum master cylinders and plastic reservoirs that are vented and require service flush every 2 years. No telling how your car has been serviced but should have had about 10 brake fluid flushes. You could very well have a stopped up ABS. I would use a PST2 or PIWIS to activate ABS while flushing to see if it would fix the issue. You may still have to replace the ABS.