brake line pressure limit - ?

[tgreenla1]

hi,

i was curious to know if anyone could give me an idea what kind of maximum pressures are acceptable on the stock 1/8"(?) aluminium brake line of a '67 912?

reason i ask is that i am trying to get the (rusted) pistons out of my rear calipers (the ones with the smaller pistons). i had the pistons restrained with a 'wooden rotor' and air pressure on the fixed line to the caliper at 160 psi, tapping with the hammer. the pistons have been soaking in pb blaster for several days too. one of the pistons refuses to budge and i wanted to get an idea of what this system (the caliper and last piece of rear line) is rated at. can i put more pressure in without damaging it?


tim

[Green 912]

Normal braking pressures go far in excess of the 160psi you are using. One thing to be careful of is that unlike a hydraulic system high-pressure air expands explosively if something lets go.

Rather than resorting to higher pressures you might want to try some heat. Heat soak the caliper with a torch (It can take a lot of heat but not red hot and it takes 5 min or so to get it hot through and through) and then put an ice cube on the head of the piston for a min or two. Then apply the air pressure. Never had one not come out when I used this method.

Another method you can use is to put the caliper back on the cars brake line, bleed it and put a C clamp on the moving piston. Now pump the brake pedal hard to blow the stuck one out. That will produce very high pressure if the rest of the system is in good condition. I use this method when I am disassembling the system and I know I have badly stuck pistons. First disconnect the caliper from the strut and move it away from the rotor. Then you can blow the pistons out one by one before you disconnect the brake line.

[tgreenla1]

thanks. i'll hold back on the air pressure.

i understand not going red hot on the caliper, but are you not worried about the rubber seals in between the caliper halves being affected? i wasn't intending on replacing those... (should i if i heat?)

i'm half way through disassembling the calipers now and reattaching the brake system at this point is not appealing. also, i know at _least_ one other piston is stuck. i don't think _any_ of my pistons have movable by hand so far...


tim

[Green 912]

You don’t have to cook them just get them hot all the way through. The rubber seals in the caliper halves are high temp, as the caliper gets hot under normal use. Don’t split the halves the O-rings are almost imposable to find.

[Roland Kunz]

Hello

pressurized air is dangerious. Pressurized luiquids don´t blow up

Grüsse