Disc Caliper Servicing/actuating pistons help

[alextrx850]

ive got the six pot YZF calipers that came with the front end that ive just fitted and am in the process of refurbishing the last 15 years of [if it aint broke..dont fix it],..now we all should know that brake fluid will attract moisture and if the fluid is not flushed and bled regularly..it will form a gummy mess inside the calipers causing a retarded movement ...ive split the calipers and have forced compressed air into the service gallerys and the cr#p that came out was shocking...these suckers ARE working -not badly.. but i need to remove the ACTUATING PISTONS from the caliper block..have used compressed air on the trx ones years ago but the pistons shot out and nearly NAILED the CAT...these ones WONT BUDGE..but they ARE moveing though.!...HOW can i get these things out.?? any trick??...cheers

[cobbadiggabuddyblooo]

put the cat back infront of them and try aagain

[Mincehead]

Pump them out on the lever, simply use the brake fluid pressure. Catch them in a clean rag of course but they won`t fly out, kitty is safe.

[alextrx850]

Pump them out on the lever, simply use the brake fluid pressure. Catch them in a clean rag of course but they won`t fly out, kitty is safe.

fair enough,but as soon as the first one pops out i will loose pressure..back to square one..and five to go..i have bled the calipers well and put them back on the bike hopeing that new fluid will loosen them up a bit more with use...but now i am thinking that if i put only ONE brake pad into the caliper block loosely [off the bike], that might make them all exit the block enough for me to grab them with some brass faced pliers..and any that are lagging...pressure them to move...like you say mince..the fluid pressure is the key...yeah yeah..i know that a set of blue spots are the go ..but where is the challenge.. ...ive never heard of this sort of technical issue on the forum as yet...OBVIOUSLY everyone services their brakes..???

[Mincehead]

Yep, that`s about the way it has to go, get them out far enough to grab them with something soft enough to grip them but that`ll not damage them.
I`ve used mole grips with rubber strips in the jaws before now, anything to provide purchase on them, then once they are out wire wool and polish or clean brake fluid to clean them up.

[phuk72]

Throw them away.

If you are going to do this properly, you will need to split the calipers and buy new seals. That will cost you more than a set of blue spots (which are better than the YZF 6 pots anyway) and save you a load of grief

[sanddune51]

Watching this debate carefully. I've overhauled lots of calipers but have never felt the need to replace the seals, upon inspection they have always been fine. I don't think pulling the pistons is such a great idea but I've heard purpose made tools are available that expand and grip the piston inside diameter.

I have always pumped out one piston (the one least needing overhaul ironically ), cleaned and polished the piston and then split the two halves of the caliper,taking care not to lose the small (square section) seals. I carefully pry out the main seal and of course the dust seal. Mostly I have noticed that there is a degree of corrosion behind the main seal.This tends to "jack" the seal onto the piston,causing the "stiction" that causes our brakes to bind on after being applied. I use a white metal bearing scraper and/or a scriber to very carefully remove this bulidup of corrorion from the seal groove and finally pollish lightly with a green scotch abrasive pad. Cleanliness goes without saying here so I won't labour the point. The caliper piston bore,mating faces and old seals are cleaned and the caliper is rebuilt with a nicely polished piston.I much prefer working on "virgin" calipers where no one has "had a go" previously. Sometimes their cakhanded efforts have rendered the pistons only fit for the scrap bin.

Now having overhauled one piston, I use two flat steel straps,drilled to accept long 6mm or 1/4" nuts and bolts to restrain the overhauled piston. I now set to work by pumping out the second piston and repeating the whole process until all 2,4 or six pistons are silky smooth and free. I now of course am the proud owner of 5 homemade restraning straps, if only I could remember where I left the bloody things

Yes, it is labour intensive. But the total cost is next to nothing and the satisfaction is immense. The results are well worthwhile.


Mark

[alextrx850]

thanks Mark for the well worded info...have found that the calipers havent been serviced in any way before..[from the amount of crud inside them] ..and found that a large philips screw driver fitted into the DISC rotor slot would make all the pistons eject and even one that was lagging move ...i made sure that there was enough fluid in the resevoir as i was pumping the brake lever too...the calipers cleaned up really well and the pressure seals seemed good as well as the dust seals, i am thinking that a quality brake oil will put vitality back into the seals somewhat and see how it performs..no leakage... and a good point there to watch for the small rubber JOINING seals that link the two caliper blocks together ..if you loose those you,r going to have to get to floor level...bet they went under the BACK of the bench [ usually do ]..ayway the photos will do...cheers

[Mincehead]

That four X gold will strip any crud off brake caliper pistons!

[alextrx850]

after quite afew of these beverages, the four EXES look more like the word BEER... so they say...a bit of a reverse psycology....and its all about LUBRICATION my friend...heh heh...the operation went well and are now in use...no brake bind and enough grip that i hope to never have to use....cheers

[Mincehead]

Are you sure you weren`t drinking the degreaser? That makes your vision blurred.

[cobbadiggabuddyblooo]

After a couple of xxxx the degreaser would taste the same

[fung]

so.....just out of interest.....how much are seals for the 6 pots?
cheers
fung