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[cam.in.head]

you may need to bleed afterwards if you do it that way it depends on if you close the nipple when the piston stops going in.not just afterwards because due to the flexibility of the seal it can move forward again a little bit and draw in some air.no harm in doing a final bleed on each wheel anyway as to be sure. i use an old fridge compressor to suck the fluid through rather than pedal pumping or pressure cap method but thats just my way.

[grifter]

What he said. 

And yes, rears more prone to issue, the pistons usually spend most of their working life 'out' of the cylinder. Ie you spend longer with worn pads than new ones, and on that vein, of course traditionally fitting new pads means pushing the old, crusty pistons with poor surface back into the caliper, also causing sticking. The gaters/boots are , meant to prevent this but these rubbers frequently turn to brittle plastic over time and cease their corrosion inhibiting. (But you know all this, im teaching you to suck eggs)

Very much like the idea of clamping off calipers to isolate the issue - though maybe not in this weather, yeh? 

Every now and again i take rear wheels off, push pistons in and then pump pedal a couple of times to keep them free. Do this especially if car rarely used. Can be done in situ if you have big pump pliers to catch edge of piston. You"ll usually get one or two that is partially seized.

[BazaJT]

Yes I do have pump pliers,I'm hoping to leave the calipers in place and do it that way however I'll have to see how it goes and play it by ear a bit on that.Failing that I've got[a recently purchased]wind back tool and can dismount the caliper and use that.At least  I know after the recent M.o.T. repairs that all the bleed nipples aren't seized in place

[Marks DTM Calib]

The best approach is to open bleed nipple and fully retract the piston, then close the bleed nipple. You may want to just then do a single peddle brake bleed to make sure that no air remains.

This was you know you have all the old fluid out the clipper (which does not happen on a standard brake fluid change) and all the air out to.

[cam.in.head]

this actually makes a lot of sense re getting all the old fluid out.i suppose if you just do a fluid flush the normal way old fluid could still be kept in the lower half of the caliper.from now on i will be fully retracting my pistons,maybee even remove caliper entirely and empty out upside down to be sure althout this may be overkill but at least you would know 99% of the old fluid is out.especially on a newly aquired or unknown history car.then keep up with two year fluid refresh should keep everything in order.this and regular maintenance re stuck pads,pistons and slider pins.its worth noting here also that a caliper with TWO stuck pads or pistons could actually have LESS pedal travel than a perfectly functioning one.also the anti squeal shims if not perfectly flat can sometimes also affect pedal travel too.
last year when i replaced two front calipers with new ones on my cav the pedal travel did indeed increase .albeit a small amount.confirmed by clamping front hoses off.thay were working correctly and retracting a small amount to give a running clearance.althout pedal travel was increased the feel and progressivness of braking was much improved and stable

[terry paget]

Would it not be a good idea, before the 2 yearly brake fluid change, to put in some worn out brake pads in the rear brakes, force out the pistons hydraulically, and clean them up with steel wool?

[Migv6 le Frog Fan]

Sounds sensible to me. 

[Nick W]

Would it not be a good idea, before the 2 yearly brake fluid change, to put in some worn out brake pads in the rear brakes, force out the pistons hydraulically, and clean them up with steel wool?

if you're going to bleed the brakes anyway, pop them right out and clean them completely. Although I'd use scotchbrite rather than steel wool

[BazaJT]

Whatever the eventual cause turns out to be,I'm certainly picking up some useful tips here Hopefully the weather will play ball next weekend/Xmas and I'll be able to try the calipers at least.If air is trapped in ABS block how would this present itself[the pedal doesn't pump up as it does if there's air trapped in the system]and how would I get it out if it is?

[terry paget]

Would it not be a good idea, before the 2 yearly brake fluid change, to put in some worn out brake pads in the rear brakes, force out the pistons hydraulically, and clean them up with steel wool?

if you're going to bleed the brakes anyway, pop them right out and clean them completely. Although I'd use scotchbrite rather than steel wool

I suppose I could take them out while I am about it. I have not had brake pistons out for 40 years, and am not sure of getting them back in again. Of course it all depends on them not being seized in the cylinders already.

[BazaJT]

Yesterday got off to a poor start so only managed to clamp off brake hoses to give that a try.Pedal improved,removing clamps on front hoses gave same result removed rear clamps and pedal went closer to floor,so it seems to be problem on the rear.Ran out of time to do anything further yesterday,was going to have a look today but washing machine decided to go pete tong

[STEMO]

Yesterday got off to a poor start so only managed to clamp off brake hoses to give that a try.Pedal improved,removing clamps on front hoses gave same result removed rear clamps and pedal went closer to floor,so it seems to be problem on the rear.Ran out of time to do anything further yesterday,was going to have a look today but washing machine decided to go pete tong

There it is again.

[BazaJT]

Don't ask me I don't know why/how that happens

[TheBoy]

Don't ask me I don't know why/how that happens

Because you are clearly hitting the strikethrough button

[Migv6 le Frog Fan]

Don't ask me I don't know why/how that happens ???

Because you are clearly hitting the strikethrough button

Difficult to work out how you can do that without knowing it.