Brake Piston Won't go back enough when changing Pads/rotors

[bagusbagus]

Having troubles pushing the piston back in enough when changing front discs & pads.
Heavy duty C clamp does nothing, using leverage and old brake pads in also does nothing much , seems like it doesn't simply wants to go in any further.

I don't have the special tool to push the piston back in, but I have changed the pads on this car previously many years ago without any much problems so I would think I have enough force with what I'm using.

Any ideas what can you do? Yes, I have removed the brake fluid container cap before doing it.

the car is 22years old & When Looking upclose I can obviously see there is some rust.
Not really sure If I'm just not pushing hard enough,not doing something correctly or there's something wrong with the callipers/pistons and perhaps they need service/new seals or replaced all together.

Attached some pics, any ideas would be highly appreciated!
Thanks.

[Mercdriver]

I would replace the pistons however when you take out the pistons you may find the bores are in poor condition so need to replace the calliper. It is the brakes after all your life might depend on them

[ImbackYo]

You may find it twists in as opposed to being pushed straight back. I had that on my tesla.

[Baldchap]

If the bleed nipple isn't rusted shut, loosen it off half a turn and try again.

[Saudade]

Baldchap said:

If the bleed nipple isn't rusted shut, loosen it off half a turn and try again.

This.

They definitely aren't twist/threaded pistons.

Though that piston looks like it has water ingress, I'd probably replace the caliper unless you get it moving freely and are confident it won't seize again.

[Moodyman1]

Lift rubber seal and WD40 or similar penetrating spray. Allow to sit a few minutes before trying to push back. If no good, the proper tool (which works for most cars) is Hilka Brake Calopa rewind. Costs about £15.

[bagusbagus]

ImbackYo said:

You may find it twists in as opposed to being pushed straight back. I had that on my tesla.

I think that's on some cars on the back, Mine just go in straight without having to turn them.

[bagusbagus]

Baldchap said:

If the bleed nipple isn't rusted shut, loosen it off half a turn and try again.

Hi, I saw this somewhere else mentioned, just curious what it would do since I have the main brake fluid cap already removed for the pressure to go somewhere?
I'm kinda ''scared'' to open the bleed nipple and get air in system, If it does nothing I guess I will have to re-bleed the brakes before I can put on the old worn thin pads back and bring it to garage to deal with it

[charltjr]

Looks fairly scabby, penetrating oil is a good shout. I'd price up a new caliper as they can be surprisingly cheap, then it's a balance as to how much value you put on your time as the whole assembly is are generally quicker/easier to swap than trying to refurb a reluctant piston.

[bagusbagus]

btw, when I Removed the Old pads on this side, one of them was totally worn to the Metal while the other one still probably had half of the pad material on it, which indicates totally uneven wear. Does that Means anything or that's nothing out of ordinary?

[Baldchap]

bagusbagus said:

Baldchap said:

If the bleed nipple isn't rusted shut, loosen it off half a turn and try again.

Hi, I saw this somewhere else mentioned, just curious what it would do since I have the main brake fluid cap already removed for the pressure to go somewhere?
I'm kinda ''scared'' to open the bleed nipple and get air in system, If it does nothing I guess I will have to re-bleed the brakes before I can put on the old worn thin pads back and bring it to garage to deal with it

It won't happen unless you pull the piston out. I'd pop the reservoir cap on, loosen the bleed nipple A LITTLE BIT and push the piston back.

Other variations include a tube or something to catch the brake fluid, which is a pretty good idea. It's mega bad for paint.

[Maxdecel]

bagusbagus said:

btw, when I Removed the Old pads on this side, one of them was totally worn to the Metal while the other one still probably had half of the pad material on it, which indicates totally uneven wear. Does that Means anything or that's nothing out of ordinary?

I'll wager the worn pad was on the piston side ? As someone's mentioned, water ingress has corroded the piston when proud of the caliper and that is preventing the piston going fully home. The uneven wear suggests that caliper has partially seized so the pad wasn't releasing fully.

[Rich Boy Spanner]

bagusbagus said:

Baldchap said:

If the bleed nipple isn't rusted shut, loosen it off half a turn and try again.

Hi, I saw this somewhere else mentioned, just curious what it would do since I have the main brake fluid cap already removed for the pressure to go somewhere?
I'm kinda ''scared'' to open the bleed nipple and get air in system, If it does nothing I guess I will have to re-bleed the brakes before I can put on the old worn thin pads back and bring it to garage to deal with it

Somebody correct me but I thought no air got into the system provided that the bleed nipple was kept upright and top? This is how I do them, crack the nipple, keep upright and push in the piston. Never had bother. That piston looks in poor shape though.

[AlexGSi2000]

Looks like there is a fair bit of corrosion on that piston.
My bet is that its the corrosion thats made it ever so sligtly wider and now wont push past the seal.
Even if you managed to push it back in you may damage the seal.

In this case I would say its replacement caliper time, or at the very least a new piston and seal kit.

[AlexGSi2000]

bagusbagus said:

btw, when I Removed the Old pads on this side, one of them was totally worn to the Metal while the other one still probably had half of the pad material on it, which indicates totally uneven wear. Does that Means anything or that's nothing out of ordinary?

Thats not normal, sounds like the piston on the side with the half worn pads has been stuck/binding, hence the other brake doing most of the work and wearing. Would imagine that should have been shown on an MOT.

[bagusbagus]

Baldchap said:

It won't happen unless you pull the piston out. I'd pop the reservoir cap on, loosen the bleed nipple A LITTLE BIT and push the piston back.

Other variations include a tube or something to catch the brake fluid, which is a pretty good idea. It's mega bad for paint.

Thanks for the Tip. Unfortunately loosening the Nipple till a speck of oil comes out didn't really help in any way getting it back in.

[PurpleTurtle]

AlexGSi2000 said:

Looks like there is a fair bit of corrosion on that piston.
My bet is that its the corrosion thats made it ever so sligtly wider and now wont push past the seal.
Even if you managed to push it back in you may damage the seal.

In this case I would say its replacement caliper time, or at the very least a new piston and seal kit.

This is my view having done loads on our cars and motorbikes. If you are vaguely technically competent then replacing a rusted old piston with a new one with new seals is really easy.

Personally I would be junking that piston. These are brakes that the lives of you and others depend on, it's not worth scrimping on them.

I use Bigg Red for mine: https://www.biggred.co.uk/catalogue/brk-caliper-re...

[E-bmw]

bagusbagus said:

btw, when I Removed the Old pads on this side, one of them was totally worn to the Metal while the other one still probably had half of the pad material on it, which indicates totally uneven wear. Does that Means anything or that's nothing out of ordinary?

In that case, as the pictures show, the piston is seized in the caliper.

Caliper refurb or replacement required.

[richhead]

E-bmw said:

In that case, as the pictures show, the piston is seized in the caliper.

Caliper refurb or replacement required.

Agree, from what you can see in the pic of the dust cover pulled back the piston is rusted, i would just change the caliper, as said before they arent that expensive. You maybe able to rescue it with a new piston and a seal kit, but often just as cheap to replace the whole thing.

[bagusbagus]

Thank you all for confirming it's busted!
Ordered a set of new Calipers £24 a piece, not that bad...