Frozen rear brake caliper.

[nsgnomad]

Nothing to do with caravans or tugs but I am appealing to the brains trust for some help.

My Peugeot 308 needs new brake pads on the rear. I have got the old pads out,  but I am having trouble retracting the piston. I believe that because of the park brake, the piston needs to be wound back (anticlockwise?). However I the piston is very difficult to turn. Have tried both directions but it will not retract. Nor will it push back with a clamp. I suspect that the piston is frozen in place by corrosion. I would normally buy a replacement but it is very difficult to find any. I have only attacked the drivers side so far.

My question is this. In order to overhaul the caliper with new seal and a hone of the bore, I need to get the piston out. Will the piston push out using the brake pedal if the caliper is removed from position and no pads in the way to restrict the piston movement? 

Your advice appreciated. Thanks

[Old Techo]

Is it a floating caliper with only a single piston on one side?

[nsgnomad]

Yes

[jr]

Hi Roger,
To far back to remember much but on my 306 there was a trick like one quarter a turn and then the piston should push back. I remember I need to fabricate something to turn the piston but not sure what I did.

JR

[Old Techo]

Roger,

I remain a bit puzzled by your question.

If the rear brakes were working then the piston moves under brake-line pressure so why do you think it maybe wouldn't move out all of the way?

[jr]

Roger,
Just done a google search: Peugeot 308 rear brake pad change. There a few YouTube’s on the item.
If you have a electric hand brake you need a code reader to tell the electric brake to release something.
A lot different to my 306.

JR

[jr]

Roger, just looked at your post again sorry never touched the piston only ever changed the pads. I would not touch the piston seal’s unless there was a leak!
If you disconnect the hydraulics you could use compressed air on the hydraulic inlet to blow the piston out.

JR

[nsgnomad]

OT& JR, according to the youtube videos I have seen, all you need to do is press the piston back into the caliper. They made it look easy. I have tried this to no avail. The piston will not move back. Not even a millimeter. As I mentioned, I have tried turning the piston and it was very difficult, but it did not recede. My pug 308 is 2009 vintage with manual handbrake.
Years ago I remember doing the brakes on my Mazda 626. That's why I has the special tool, a cube shaped thing with different protrusions on each side that fitted onto a 3/8 sq drive. In the case of the
Mazda, the piston wound back, not a combination of turn and push like JR suggested.

In case you might think I am not pushing on the piston hard anough, I did try using a large 'G' clamp, tightening it as hard as I could with 2 hands, then with the caliper removed from the vehicle I tried again using a bench vice. Still nothing.

I mentioned I have not yet touched the passenger side caliper. Those pads are down to metal so I know that piston is moving. The drivers side pads are low, but not as bad. (Maybe because piston is not moving).

If you don't have any further suggestions, I might need to have a go at the passenger side caliper since the piston is moving, to work out how it is done.
I agree, JR, I would rather not touch the seal if I don't need to.  There is no leak.

Murphy is alive and hiding in my garage. 😣

[spaceland]

Jan 12, 2023 22:38:45 GMT 10 nsgnomad said:

OT& JR, according to the youtube videos I have seen, all you need to do is press the piston back into the caliper. They made it look easy. I have tried this to no avail. The piston will not move back. Not even a millimeter. As I mentioned, I have tried turning the piston and it was very difficult, but it did not recede.

It sounds like you are out of your depth here. With something as important as brakes, I would be admitting defeat here and taking it to someone who knows about those things.

[jr]

Hi again Roger,

If you tried a G Clamp and the piston would not move and your hand brake works on the disc and not a separate drum then there must be something that needs to be turned released or screwed. If the piston has a couple of slots in it then there is a good change a special tool is required.


Have a look at this video it is not your model vehicle but sure looks like what you need to know!



This is the kind of thing a Peugeot work shop should have.

www.halfords.com/tools/hand-tools/tool-kits/laser-pneumatic-brake-caliper-rewind-tool-kit-669142.html?stockInventory=undefined


JR

[Old Techo]

Roger,

I have unsuccessfully followed the logic/direction of the conversation, helped by no answer to my question

I gathered you believed the piston was rather stuck in its bore and you had in mind removing it for honing or the like?

Rather than blast the piston out 100% by the use of brake-line pressure I'd use some wooden/metal spacers to limit piston travel and to see if pushing it out with the brake pedal actually freed it up a bit and maybe permit piston rotation and possibly expose any piston corrosion for examination.

To push the piston home on my GTHO discs I used an old worn brake pad, drilled a hole in the centre, welded on a nut, and using a bolt through it to wind in the piston.

[jr]

OT, from my take on the post is that the brake pad piston needs to be pushed back to make room for the new pads but as it cannot be moved back it is assumed it is seized so when the piston is finally removed new seals will be required.

I personally think it is not seized just that the internal ratchet that takes up the hand brake adjustment needs to be released. Many Peugeot’s hand brakes operate directly onto the disc brake pads so inside the piston cylinder is an internal screw or ratchet that keeps the handbrake adjusted which needs to be released.

This is the tool I think that is required, note this tool has the pins to fit in the piston slots.


Note the slots on the piston for the tool to fit in and turn.


The tool in operation


Note the locking plate that takes up the winding in force


JR

[Old Techo]

Thanks JR

I was with you earlier on the handbrake thing but I got the impression that the piston would not move back even the slightest, nor rotate, except barely.

Wouldn't a piston handbrake restriction only be the case when the handbrake was not fully released?

I can only imagine the engineering thus... the piston normally moves in and out hydraulically over a very short distance. After the foot-brake pedal is released the piston seal distortion normally pulls it back a few thou. Then disc rotor runout and/or road shocks may knock it back a few more thou. Then the handbrake system should when released ensure there is adequate free play to allow at least quite a few more thou. The sum total ought to be enough to permit some visible movement of the piston but I gather Roger saw none.

The simple piston 'binding' test is as I suggested earlier and with the caliper still off use some spacer or packing to permit the piston to travel out only say 5mm then test how easily it can be pushed back.  If the handbrake is the issue the piston should push back easily until it hits a sudden premature stop. 

[jr]

I agree OT that there should be some movement, but it is very minimal and would not be easy to see with the rubber boot hiding it.

If you have the time have a look at these two links the first clearly shows the special tool in operation and the second is a explanation of one way these hand brakes work inside the piston.

Fast forward to about the 3minute 15second mark:


Have a look at this explanation of how the handbrake auto adjust can work.
www.engineeringinspiration.co.uk/parkingadj.html
It appears that we have a spring steel strip (ratchet) that runs on a fine threaded screw and will allow movement forward by clicking over the thread when the brakes are applied but will not allow it to go back much! So, to release the piston you need to screw the piston just like unwinding something.

JR

[Old Techo]

Thanks JR for going to all that trouble

That all looks pretty convincing to me and that Roger's initial logical perception of 'piston binding' is explained.