Front Brake piston won't budge?

[Old Colts in Oz]

Hi all,

I've replaced many brake pads on different cars over the years so was surprised yesterday when I tried on my VS wagon and failed. I can't get the brake piston to move on the left side. I was using a big G clamp and had the top of the master off etc. After spending ages on it I gave up and put the wheel back on. Today a mate told me that some cars actually have a set up where the brake piston screws in. Is this the case with the VS design? If not, any other ideas? I've searched the forum and the "how to's" but couldn't find anything. Thanks in advance

 

[BoNeZ-01]

Far as I know the only screw in pistons were for the rear brakes, where the calliper is also used as the hand brake, but not in* these models(from memory).
Ford's also have this rear calliper/handbrake set-up.

Sounds like it might be time for a calliper rebuild kit?

One other way you can try that works for me sometimes, is undo the bleeder, then try pushing the piston back.

You'l need a second person to help you with this next method-
Have the calliper installed as normal first, with the rotor in place, and with the old pads in, not new ones, so you'l have extra clearance from older worn pads.
With the wheel on, but jacked up just enough to turn, have the other person start the engine, and start working the brake, not harshly, just on, then off.
Grab the wheel and try to spin it while the brake is being worked to make sure the piston isn't completely seized.

Turn the car off and take the wheel and calliper back off, then undo the bleeder on the calliper enough till it starts to weep fluid.
Have the other person ready with the bleeder spanner, then push as hard as you can on the piston, till you can't push any more(make sure you push as evenly across the piston as possible, so the piston goes back square, not one side more than the other, which will just make it bind up and not go anywhere! lol), then have the other person quickly close the bleeder.
It may take a few goes, but if done right this 'should' give you the clearance you need for the new pads.
Make sure you finish off by bleeding the brake system as normal after all done.

 

[RX25SE]

Did you try pushing from the bottom of the piston? ie The threaded part of the G clamp inside the piston.

 

[Brett_jjj]

Ive ran into a couple of ones stuck like that.I removed the caliper,layed it on the ground and got a hammer with a wooden handle and put the handle into the piston and leant on it heavily.They ended up going back into the caliper bores no worries both times.The only thing is you will have to bleed the brakes because the caliper has been removed.The pistons dont screw into these calipers at all.They just push straight in and out.

 

[Old Colts in Oz]

Thanks guys, some handy info there. I'll give all that a go asap and see what I can find. Hopefully I won't have to take the caliper right off but it's looking likely!

 

[Brett_jjj]

By the time most brake pads have worn out its usually time for a brake fluid flush and change anyway.So bleeding the system front and back will flush out the old fluid and it will be replaced with fresh stuff as its pumped through from the master cylinder,just make sure the fluid coming from each wheel is the fresh stuff you have topped up the master cylinder with.If its not and it still looks dirty/old, keep pumping it through until its clean...Bleeding the brakes only takes half an hour (at the most), and around 2 bottles of fluid (depending on their size).If you are not sure about anything with the brake bleeding, just ask here and we can step you through it.Its easy.

 

[RX25SE]

By the time most brake pads have worn out its usually time for a brake fluid flush and change anyway.

Very true indeed.


But hardly ever done!

 

[baza]

a good tip when you bleed the brakes , if the master cylinder is old ,and or the fluid is dirty , do NOT push brake pedal to the floor. place apiece of timber on the floor under the brake pedal , about 40 - 50 mm thick. normally when you use the brakes the piston in the master cylinder moves only a small distance . if after alength of time the piston is pushed a lot further [ bleeding ] grit and crap in the cylinder can tear or damage the rubber seals on the piston , then you are up for a M C overhaul , or maybe a new master cylinder. that caliper with the stuck piston sounds bad , not normal at all , should push in easy with g clamp . seems as if the piston has been pushed into the caliper bore out of square and scored the bore and jammed itself. take caliper off car and force the piston out with compressed air in where the brake hose bolts on. and keep your hands away from piston when you use the air compressor.

 

[BoNeZ-01]

a good tip when you bleed the brakes , if the master cylinder is old ,and or the fluid is dirty , do NOT push brake pedal to the floor. place apiece of timber on the floor under the brake pedal , about 40 - 50 mm thick. normally when you use the brakes the piston in the master cylinder moves only a small distance . if after alength of time the piston is pushed a lot further [ bleeding ] grit and crap in the cylinder can tear or damage the rubber seals on the piston , then you are up for a M C overhaul , or maybe a new master cylinder. that caliper with the stuck piston sounds bad , not normal at all , should push in easy with g clamp . seems as if the piston has been pushed into the caliper bore out of square and scored the bore and jammed itself. take caliper off car and force the piston out with compressed air in where the brake hose bolts on. and keep your hands away from piston when you use the air compressor.

Well said baza. :thumbsup:
But just adding to that last bit about forcing the piston out- "IF" reusing the piston, place a folded up rag or thin piece of wood, on the opposite side where the pad sits.
That way, when the piston comes flying out, it wont smack in to the other side of the calliper and get damaged.

 

[RX25SE]

You can also use the master cylinder to push out the piston. Remove the offending caliper (leave the others installed) and pads, get an assitant to SLOWLY push the brake pedal until the piston pops out.
This method is slower and messier than using compressed air but there is no risk of sending the piston across the workshop!

I still think that a correctly applied G clamp will free the piston with no need to remove it.