17-01-2015, 10:58 AM
(This post was last modified: 17-01-2015, 11:07 AM by pug306driver.)
I presume front caliper pistons??
if they are seized solid ( difficult to imagine on a car with servo ) or very stiff, do not disconnect the hydraulics yet.
use the hydraulics to your advantage...............peel back the boot ( piston boot or gaiter ) and lub piston with brake fluid, then with an assistant pumping the brakes ( with caliper swung off the disc etc ) and with good communication, pump out the piston as far as you dare without it coming out completely ( so that you still have hydraulics to help you ) ....they using a g clamp and wood to protect the caliper and piston, gently force the piston back in ( excersising the piston) .
if very stiff use a heat gun (hot air ) to help. sometimes I place the caliper assembly in a bucket of boiling water ( kettle full ) to heat caliper and piston as a whole and then excerside the piston. once free, pop the piston out and disconnect the hydraulics. the "land " between the caliper hydraulic seal and the outer gaiter usually corrodes, as well as the piston, to make the piston very stiff and not self release ( piston pulled back due to hydraulic seal acting as a spring ( seal deforms when piston is pushed out via the fluid and then un deforms back to original shape, taking the piston back with it ) .
use red rubber grease for reassembly of the piston and hydraulic seals etc. piston should be a thumb pressure to push back in with the m/cylinder cap off..........
rears are a bit more involved as the pistons need to be wound back in so need to turn or rotate.
remove the bleed nipples on the bench with the seals removed as heat can be applied...........do not shear them off!!!
when clean and painted ( golden opportunity here ) reassemble, fit and bleed.
deal with one side at a time, and make a "brake union blocking device" to block the metal pipe union or complete fluid loss,one that screws into the union on the metal pipe.........else total fluid loss and system will need total bleeding ( other bleed nipple problems etc )
if they are seized solid ( difficult to imagine on a car with servo ) or very stiff, do not disconnect the hydraulics yet.
use the hydraulics to your advantage...............peel back the boot ( piston boot or gaiter ) and lub piston with brake fluid, then with an assistant pumping the brakes ( with caliper swung off the disc etc ) and with good communication, pump out the piston as far as you dare without it coming out completely ( so that you still have hydraulics to help you ) ....they using a g clamp and wood to protect the caliper and piston, gently force the piston back in ( excersising the piston) .
if very stiff use a heat gun (hot air ) to help. sometimes I place the caliper assembly in a bucket of boiling water ( kettle full ) to heat caliper and piston as a whole and then excerside the piston. once free, pop the piston out and disconnect the hydraulics. the "land " between the caliper hydraulic seal and the outer gaiter usually corrodes, as well as the piston, to make the piston very stiff and not self release ( piston pulled back due to hydraulic seal acting as a spring ( seal deforms when piston is pushed out via the fluid and then un deforms back to original shape, taking the piston back with it ) .
use red rubber grease for reassembly of the piston and hydraulic seals etc. piston should be a thumb pressure to push back in with the m/cylinder cap off..........
rears are a bit more involved as the pistons need to be wound back in so need to turn or rotate.
remove the bleed nipples on the bench with the seals removed as heat can be applied...........do not shear them off!!!
when clean and painted ( golden opportunity here ) reassemble, fit and bleed.
deal with one side at a time, and make a "brake union blocking device" to block the metal pipe union or complete fluid loss,one that screws into the union on the metal pipe.........else total fluid loss and system will need total bleeding ( other bleed nipple problems etc )