10 replies to this topic

[RawlinsGTR]

Hi all,

I was replacing my 1997 Rover Cooper's brake discs and pads, because they felt spongy and a bit slack, when I came across a problem.

I tried to push the pistons in the calipers back so that they were flush with the caliper (enabling me to fit the new pads in), but they don't go all the way, no matter how much force I put on them. [Here's a picture to show how far they go back:]

 IMG_20110907_165301.jpg   730.53K   17 downloads

So I had a look on TMF for anything about this problem, and found some replies saying that they might be seized.

I wanted to test this, and tried pressing the brake pedal and seeing what the pistons did. On both sides, only one of the pistons moved, whilst the other stayed still. [Here's another picture to show what they looked like after I'd pressed the brake pedal a few times:]

 IMG_20110907_165408.jpg   752.92K   17 downloads

Does this mean that they are definately seized, or is there a different problem?

Any help would be appreciated,

Thanks,

Simon.

[R1minimagic]

The pistons look really badly corroded so i would just scrap them and buy a good 2nd hand pair which can be had for around £20 or less if you are lucky!

[Kat7Racing]

Looking at them id prob replace the pistons and seals as a matter of course as they arnt expensive and yours are very corroded. Re the pictures....move the one that moves back into the caliper then clamp it so it cant move.....use pipegrips, welding clamps etc.... then press the pedal...... this should move the non moving one out, get it moving then unclamp the original, get that one moving again and you should be able to get both pistons out.... replace pistons and seals and bleed brakes properly. Just my thoughts.... others may differ

[yellowmonster]

I can't see how bad the pistons are corroded further up their sleeves, but if you've experienced dragging brakes I'd certainly pay more attention to them.
It's normal that, when non-obstructed, just one piston moves: pressure keeps pushing on both until one gives way.
When the piston finally meets an obstruction and pressure builds up further, the second piston will eventually move too.
Make sure they both slide freely in and out and have no sticky points, in doubt renew pistons and seals.

[RawlinsGTR]

I can't see how bad the pistons are corroded further up their sleeves, but if you've experienced dragging brakes I'd certainly pay more attention to them.
It's normal that, when non-obstructed, just one piston moves: pressure keeps pushing on both until one gives way.
When the piston finally meets an obstruction and pressure builds up further, the second piston will eventually move too.
Make sure they both slide freely in and out and have no sticky points, in doubt renew pistons and seals.

Ah - that's exactly what it did when I tested it with the disc inside the caliper; one piston moved all the way in until it touched the disc, and then the other piston moved in.

Since that probably means that the pistons aren't seized, is it worth buying new pistons and seals so that I am able to push them back until they are flush with the caliper? Because whether they're seized or not, we were unable to push them in all the way, thus the new brake pads wouldn't fit.

Just another quick question; when we were pumping the brakes to test the pistons, one of them popped out, and brake fluid started coming out. Is it normal for the pistons to pop out if there is nothing to obstruct them from doing so?

Thanks,

Simon.

[MiniLuke]

I can't see how bad the pistons are corroded further up their sleeves, but if you've experienced dragging brakes I'd certainly pay more attention to them.
It's normal that, when non-obstructed, just one piston moves: pressure keeps pushing on both until one gives way.
When the piston finally meets an obstruction and pressure builds up further, the second piston will eventually move too.
Make sure they both slide freely in and out and have no sticky points, in doubt renew pistons and seals.

Ah - that's exactly what it did when I tested it with the disc inside the caliper; one piston moved all the way in until it touched the disc, and then the other piston moved in.

Since that probably means that the pistons aren't seized, is it worth buying new pistons and seals so that I am able to push them back until they are flush with the caliper? Because whether they're seized or not, we were unable to push them in all the way, thus the new brake pads wouldn't fit.

Just another quick question; when we were pumping the brakes to test the pistons, one of them popped out, and brake fluid started coming out. Is it normal for the pistons to pop out if there is nothing to obstruct them from doing so?

Thanks,

Simon.

Yes, they pop out. Yours will need bleeding thoroughly now. Even clamping one piston to get the other out might not work now air is in the system.

I think they won't push right back in because the leading 1/2 cm or so is corroded. If you force them back in the rough surface will knacker the seals anyway.

Buy new calipers. Or if you are confident new pistons and seals.

[RawlinsGTR]

Of course, they will need bleeding. Thanks for the info though.

Simon.

[bmcecosse]

Get new stainless pistons - and new seals. These are well past their use-by date.....

[MiniLandy]

Get new stainless pistons - and new seals. These are well past their use-by date.....

+1 JonSpeed do a good set of stainless pistons at a good price.

Replacing the pistons and seals makes a hell of a difference, and you might as well have a good look at all your brake lines for heave corrosion, and fit new flexi hoses or braided steel ones if they look a bit suspect (old).

[jaydee]

Many companies are selling reconditioned calipers on exchange rate, if you're not confident in replacing pistons/seals or dont want the hassle.

[RawlinsGTR]

Thanks for the replies. I am confident in replacing the seals and pistons, but I just couldn't decide whether it was worth just to replace the whole caliper whilsts I was at it. But it seems that replacing the pistons and seals is probably the cheaper option.

I'll let you know how I get on.

Thanks,

Simon.