Pistons & Master Cylinder

Roger Mellie Man on the Telly

Pushing/rewinding pistons after a pad change. Is it absolutely necessary to open the bleed valves? I've heard that it's possible to damage the master cylinder seals...

Those Pakistani lads on Youtube don't bother to open the bleed nipples. They don't bother with axle stands either.:)

CJhaughey

Roger Mellie Man on the Telly wrote: »

Pushing/rewinding pistons after a pad change. Is it absolutely necessary to open the bleed valves? I've heard that it's possible to damage the master cylinder seals...

Those Pakistani lads on Youtube don't bother to open the bleed nipples. They don't bother with axle stands either.:)

I always open the bleed valves when pushing the pistons back, a lot of crap accumulates in the caliper and if you open the bleed nipple it gets pushed out of the cylinder, when you bleed them its replaced with fresh fluid.

i57dwun4yb1pt8

I plan on doing this and anyone / any guide ive seen says block off the brake hose locally then bleed at the caliper locally
instead of pushing back pistons openly to the MC

for me = rather be safe than sorry , specially as a newbie .

dooroy

I always clamp the flexible pipe and open the bleed nipple to allow the piston to be pushed back , one of my reasons being as stated by cjhaughey.
Also there can be the possibility that in some cases forcing the fluid back to the master cylinder could cause a seal to 'reverse' itself . I think it happened mostly with some Opels in the past - but I presume other cars could suffer also.

corkgsxr

I never had a issue doing it but lately Iv started clamping the line and opening the nipple as I push back


My reasoning, the fluid in the caliper is most affected by heat so your getting rid of worst fluid and any air built up.

Roger Mellie Man on the Telly

Just noticed that VW's Elsawin workshop manual technique only advises the technician thus: "Before pressing pistons back, draw off some brake fluid from reservoir with a bleeder bottle. Otherwise, particularly if reservoir has been topped up, fluid will overflow and cause damage."

i57dwun4yb1pt8

oh those VW wildmen !