danny_k

Replaced front rotors and hardware, and bleed all 4 corners this weekend. Everything seemed pretty standard. Utilized having a second person pumping the brakes to bleed them.

I now have a sticky rear caliper(s), the pistons dont seem to retract causing the rear brakes to drag. Important to note all i did was bleed and clean the rears as the rotors and pads are still in good shape. After parking for a little while the calipers magically free up.

• Bringing a laser temp gauge home today to see if its both calipers or just one ( think its both).
  
• I re-bleed the rear just to double check no air, all looked good.
  
• The fronts are working just fine.
  
• I had no issues prior to bleeding.
  
• Lines are SS braided.
  
• Previous Owner rattle canned the calipers, and didn't appear to disassemble or even remove them from the car (overspray concerns?)
  
• PSM light is now on
  
• its definitely caliper issue, not ebrake. I know this because if i hit the brakes the calipers stick and hold that brake position.

I scoured the forum and internet and for the life of me cant find anything that explains it. Part of me wants to rebuild all 4 calipers, toss new SS braided lines on and see if that helps. But that is a good bit of work if its not needed.

Macster

If the pads are just lightly remaining in contact with rotors my guess is the PO's paint job is to blame.

Paint was applied to the boots and this is enough to interfere with the natural tendency of the piston seals to retract the piston slightly and thus allow the pad to move away from the rotor. Because of the paint then this doesn't happen.

Believe it or not once in a while I fix "squealing" brakes with both my Boxster and Turbo by washing the brakes, which rinses away the considerable amount of dust that accumulates. This dust gets on the dust boots and like the paint interferes with the pistons retracting slightly. The result is the pads drag and after a while develope a squeal. Not bad but it is irritating to hear.

If the pads are remaining applied with any force against the rotors that is an internal problem. Fluid pressure is not falling off when the brakes are released. Sometimes a brake line can degrade (internally) and interfere with brake fluid flow. Steel iines can corrode or if lined with something this liner can go bad -- swell or peel/flake -- and interfere with the flow of fluid. While braking action may not be affected to a noticable degree the brake line degradation interferes with the fluid flowing away from the brake calipers. Or the brake calipers get bad and the pistons hang up or stick.

If the paint is to blame then the solution is I believe you'll have to disassemble the calipers and replace the dust boots. 'course, while you are there you probably should consider a caliper "rebuild".

Once you get the calipers apart if you find considerable debris in them this suggests brake lines upstread are degrading and shedding material.

danny_k

Thanks Macster.
Dragging brake pressure is correlated with how hard you hit the brakes. It essentially holds the max brake pressure you have applied. So in my case i went out and braked at 50%, the rear caliper(s?) then held that 50%, and it felt like the ebrake was most of the way up. Defiantly not a light dragging of the brakes, its heavy and very substantial.

You could be headed somewhere with washing debris down onto the piston. I did clean all the suspension components and calipers while i was doing the bleeding.

Borrowing a pressure bleeder from a friend, may give that a try but dont have high hopes for that making any difference. To me is such a substantial dragging force that alot more is going on then a tiny air bubble. The timing is what i find suspicious.

32krazy!

sounds like a collapsed brake line. brake pressure pushes past the collapsed point but line pressure wont release and allpw fluid back into the system. start with the lines.

and as a self serving comment
https://rennlist.com/forums/parts-ma...ake-lines.html

napoleon1981

Did the calipers flow nicely when you opened the bleeder valve? Was there any junk coming out? I'm not a fan of the pumping the master cylinder method, as you press the pedal past regular travel, and can damage the interal seals. Too be honest it almost sounds like the master cylinder is not releasing the circuit.

I would be inclined to take the caliper off, replace the dust boots and square cut seals and brake line.

I just rebuild my front calipers, and I could tell that the new square cut seals were much tighter. Since it is the square cut seal that pulls the piston back, I wonder if they have just aged too much.

r6vr6

What happens if you pull up on the brake pedal?

fpb111

What year? PSM? Sounds like ABS or PSM is activating. I would check the fronts again. It sounds like the system may be sensing a front-rear imbalance and is jumping in to save your life.
Could be that you got air in the stability management system pump and need to bleed with a Piwis, or whatever Porsche calls their computer.

danny_k

Quick update in case anyone needs this in the future, although it wont be a super specific fix.

1. Regarding sticking rear caliper. i replaced all flex lines and rebuilt all 4 calipers (zuekenhaus parts kit). This fixed the sticking rear caliper issue.

2. Regarding the low brake fluid/PSM lights. The float for the brake fluid level was being held down. Unfortunately during this process old hood struts allowed the frunk to fall when i had a small funnel in the reservoir, causing a the tinyiest depreesion pushing the float down. A small corrective adjustment freed the float up to do what it does best... float.

thanks so much for everyones help!

32krazy!

pics of the float?

danny_k

https://www.google.com/search?q=996+...1CYgfvoMOzd1M:

thats the pic on 6speed I saw that prompted by check.