autobonrun

79 911 SC. One of the two pistons on my driver side rear is completely frozen in the caliper. The other is half way out and clamped to hold pressure. I’ve soaked the stuck piston in PB Blaster overnight and applied heat to the caliper body as well. Using the setup below, I applied 120 psi and get no movement. Any other suggestions before I buy another caliper?

If I have to buy another should I just buy a rebuilt unit? It’s a quarter the price of a new one.

theiceman

sounds like its jammed... i would get the special tool for pushing it back in first ... or a good quality C clamp... the tolerances are very tight and if its **** eyed it likely has to go back in before it can come out...

i ran into this exact issue when rebuilding mine..

autobonrun

I took your advice and pressed it back in. There was maybe a 1/4 inch of movement. Applied air again and it popped out. See photo. In this position they should both come out now. Thank you very much. Pressing it back in did the trick.

I can’t imagine working on a 4 or 6 piston caliper.

r911

how smooth is the boore? the piston sides?

and how old was the brake fluid?

autobonrun

The pistons look fine. The cylinder bore had varnish but no corrosion. I was able to remove any varnish using a soft emory cloth.

The brake fluid was old, too old. I’ve flushed the front brakes within the last two years but not the rears. I’m going to flush all four during this exercise. I built a power flusher a few years ago using a garden sprayer with fittings and a hose. I secure it to the reservoir overflow and I’m able to sit at the wheels and flush/bleed them alone. Works great. As backup I always throw a blanket over the reservoir in case the hose comes loose. It shouldn’t because I use a clamp but better to be safe.

r911

I use that same setup, but don't put any brake fluid in the sprayer.

This is a good time to replace all the rubber brake hoses with new from the dealer. (not to mention any old rubber fuel hoses)...

Congrats on getting the piston out and finding no rust!

autobonrun

There were just too many air leaks with the setup above. I couldn’t easily build up enough pressure to move the pistons out. So I made a visit to a tool store and they recommended a fitting that fits directly into the caliper. Although I don’t use Teflon tape on brake line fittings, I put a little on the threads and screwed it in snug but not tight. I didn’t want to damage the threads in the caliper. This has the same valve on the end as a tire stem so it’s simple to apply pressure. Photo below has the details. For safety I covered the caliper with a heavy towel and wore safety glasses before I applied pressure.



Fitting

Fitting in caliper