Avid sticky pistons & bleeding – stupid contraptions

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  • Avid sticky pistons & bleeding – stupid contraptions
  • TandemJeremy
    Member

    The seals need to be lubricated. You might get away with pumping them part way out and using brake fluid to lubricate them but the best way IME / IMO is to remove the pistons completely and smear with red rubber grease and refit. It might be best to have new seals to hand tho as removing and refitting pistons can damage the seals. With fairly new brakes you might get away with it.

    boobs
    Member

    my ss pads are fine and went in ok. Sometimes pushing the pistons back and letting a little fluid out helps. If you replace the pistons can I have the old ones :-)? Good luck

    stumpy01
    Member

    TJ, presumably they will need a bleed, once the pistons have been out??

    I tried doing this with the pistons in place on the rear, by pumping pistons out (holiding free piston in place to get stickier one out) and cleaning with a cotton bud. When they were as clean as I could get them, I then tried to smear fluid around the pistons and push them back into place. Not sure how successful I was in getting fluid onto the seals, but it doesn’t seem to have made much difference to the rear.

    I might get the pistons out, have a proper clean up of the area and lube the seals that way. Is red rubber grease something that my LBS is likely to stock?

    boobs – great forum name

    ahem

    i’m currently stripping down my old Juicy 5’s. i always had problems with pads sticking as well, pistons not returning. you can get the pistons all the way back if you loosen the bleed screw on the lever slightly first. getting the pistons out is a pain. as it suggests in the manual, you can do it by pumping compressed air in there

    two of the pistons were worn along one edge where the pad bottoms out against the caliper under braking load, which probably explains why they stick. someone explain why plastic pistons are meant to be a good thing? oh yeah, it’s cheap

    speaking of new pads, i just got some Superstar ones too. one of them had actually disintegrated INSIDE the packaging! i’d heard bad things but that’s just silly

    ps, to remove the piston, do not pull on the metal boss in the centre. i did this last night and it came off! bugger

    Premier Icon simon_g
    Subscriber

    I’m having fun with this too – fitted a secondhand set of Juicy 7s and there’s so little clearance the rotor drags.

    Pushed pistons out, used a cotton bud with brake fluid to go around the sides of the pistons, pushed back and forth, seemed to be going nice and freely.

    Bled fully, a bit of air came out, nice solid lever feel but still the tiniest amount of clearance as the pads are sat right next to the disc.

    Tried turning the pad adjustment dial both ways, no sodding difference. Even tried strapping the levers to the bars overnight – again, no difference.

    What’s next? A full caliper service? Or off to the bin/ebay and get some Shimanos?

    mk1fan
    Member

    Is it too late to say you don’t need to take the pistons out?

    All you need to do is – with the pads and the wheel out – spray some lube into the calliper. If you do this with the pistons ‘out’ slightly the lube will draw back up to the seal. Leave for a couple of minutes to soak and then gentley pull the lever to move the pistons further out. Clean off any gunk and re-lube. Allow to soak for a minute then ease the pistons back in.

    TandemJeremy
    Member

    Do not use spray lube – some are incompatible with the seals and will cause them to swell and stick

    If you remove the pistons you will need a complete rebleed

    Use the correct products for brakes. Brake fluid of the correct grade, red rubber grease or silicon lube for the seals.

    mk1fan
    Member

    Simon_g,

    Try opening the pad seperator spring up a bit more.

    PCA doesn’t move the pads at all but increases and decreases the size of the lever reservior to produce throw on the lever. You should bled the brakes with the PCA all the way ‘Out’ and then move it ‘In’ to get the desired lever throw. As the pads wear you move the PCA ‘Out’ to maintain throw.

    Premier Icon simon_g
    Subscriber

    That’s worth a go – ta.

    mk1fan
    Member

    I’ve used GT85 and Halfords PTFE lube without problems.

    stumpy01
    Member

    So then…..brakes worked excellently until I needed new pads on the rear. Pushed pistons back as required, removed old pads, cursed and swore trying to get new pads in. Got them in…..oh, they bind on the rotor…..

    Google……..20 mins later……

    ….appears to be that the pistons aren’t retracting – common Avid problem and can sometimes be solved by moving pistons in/out while cleaning/lubing…..attempt to do this….one piston seems to be sticking more than the other, another Avid common problem…..but get it to the point where it’s not so bad, although at one point a piston did slip out, so I have probably put air into system……buy bleed kit.

    ….bled rear brake yesterday having watched video on Youtube. He appeared to leave pads in and use spacer, but I wanted to get pistons as far back as possible (pads were part worn at this stage and didn’t want to bleed with part worn pads). Take out pads and put in bleed block as supplied in bleed kit, which suprisingly doesn’t push the pistons all the way back…..hmmmm. I bled the brake and loads of air came out, but pads are still slightly binding and lever feel isn’t all that much improved.

    Move onto front brake as pads need replacing….put new pads in and they also bind slightly, but lever feel is rock solid. Take pads out and check pistons and they are also sticking, more on one side.

    Feeling a bit miffed that £270 worth of brakes are working pretty poorly after just one set of pads…..I replaced my Julies with these are they were causing me grief at pad change time, but these seem just as bad. It seems that the only option is to buy a set of piston re-furb kits for them and take them to bits…..? Is this normal??!!

    The pads are SSC pads and perhaps are not quite the same size as original Avid pads but I don’t have a CMM to measure this on. Even this though doesn’t explain the sticky pistons…..
    And shouldn’t the bleed block push the pistons ALL the way back into the caliper housing??

    Aside from that, rear brake was really easy to bleed but am a bit peeved with these sticky pistons….I don’t really fancy 6hrs of brake drag on Sunday at the Enduro6.

    TandemJeremy
    Member

    Lucky then Mk1fan. It depends on whether your brakes use dot or mineral oil and the typoe of seals but oil on seals designed for dot fluid will destroy them. Probably the seals did their job and didn’t let any oil past the outer lip which saved your seals.

    Premier Icon simon_g
    Subscriber

    Nope, even with the pad separator spring so open it’s tricky to get pad in, give the lever a couple of pulls and the inside piston is sticking out a mm or two and the pad drags the rotor. Nuts.

    LBS charges £35 a caliper for service/overhaul. More importantly, I want to ride this weekend and my old brakes are already on my mate’s bike. 🙁

    mk1fan
    Member

    I run Avid’s with 5.1 DOT. I’ve cleaned my brakes as above for three years or so. I haven’t had any seal failures – except for one on a s/h calliper and I was preping it before use – no sticky pistons either.

    Now I’ve said that, I’ll probably have complete failure of all my brakes this weekend 😆

    As my lube supply is running low I think I’ll look at the silicone lubes as replacements.

    Simon_g, realign the calliper and it should now stop deragging.

    TandemJeremy
    Member

    mk1 fan – maybe they are compatible then. certainly not recommended as one cannot be sure what is compatible and what isn’t.

    tang
    Member

    my 5s while good when they work, have been nothing but trouble. pad change nightmare, stuck pistons, various rebuilds. shimano xts in the post now.

    Premier Icon u02sgb
    Subscriber

    Had huge problems with my 5’s but seem to have fixed them. I think the first set of seals may have finally gone (after spraying disc brake cleaner into the caliper and destroying the seals… ahem.. wouldn’t advise doing that:). Was having problems with them before this though.

    Fixed by:
    1) get a new seal kit (called a “pressure foot kit”) for £10 and not the £25 one with all the screws from chainreaction.
    2) dissasemble, you can use a track pump with the plastic “inflatables” adaptor to blow the pistons out. Be careful I took a chunk out of my wall as it flew across the room.
    3) replace the seals and wipe them with red rubber grease (I got some off ebay for about £5).
    4) reassemble and bleed.

    Mine have been rock solid ever since, the rubber grease should also make the pistons move more smoothly. Was quite disappointed they packed in so quickly though. The front brake that hasn’t had degreaser in it seems to be leaking a bit too and it’s only two years old.

    I’ve replaced one of them with an avid Elixir, which is a much nicer brake and hasn’t had any problems with bleeding so far.

    Stu.

    stumpy01
    Member

    u02sgb – think I will be giving this a go and perhaps regularly removing pads, cleaning up inner caliper and re-greasing with this red rubber grease stuff.

    If I still have issues then I will be getting shot of them, as soon as I have some spare cash.
    I’ve got the service manual for the calipers, but how easy is it actually to do?

    Premier Icon u02sgb
    Subscriber

    If you can bleed them, you can strip and reassemble them. I found bleeding to be a bit difficult to start with. A few tricks that made it easier:

    1) Follow the instructions to bleed the caliper and hose then remove the caliper syringe.

    2) do a quick bleed of the lever, in between trying to pull air out with the syringe pull the lever to activate the brakes (this builds up the pressure in the hose and pushes the air up to the top of the system). It also helps to dislodge the air bubbles around the lever mechanism.
    3) Now pull the lever and zip tie it to the bar so it’s permanently on.
    4) Leave overnight or for a couple of hours, then rebleed the lever.

    The air takes a bit of time to work it’s way up to the lever sometimes so it’s worth taking a bit of time over it. If you find the brakes are at all spongy you probably only need to rebleed the lever end.

    One other thing, if you store the bike upside down any air will work it’s way back to the calipers and give you spongy brakes again. This probably won’t happens straight away but you’ll probably get a little air working it’s way in over time. I also found it was worth cleaning the discs with proper disk brake cleaner every couple of months. Just don’t spray it into the caliper!

    They’re amazing brakes when they’re set up properly but there are quite a few problems with them.

    Stu.

    So what we're saying is, don't use brake cleaner to clean the brakes? does it phuck em?

    Or are we saying to use it on the pads but NOT the caliper?

    Short of fleeBay, Where can I get some 'o' this red rubber grease stuff? Is there an alternative? or will the PACE grease be reet? The PACE stuff is specifically for forks, so would imagine it's o'reet on brake seals?

    1 massive thing that AVID left off the bleed instructions that make your brakes as hard a slab of over-done, 3 month old flapjack, is that you need to push fluid back to the caliper/lever.

    No need to disassemble, just spray the pistons with some GT85 (with pads removed, durrrrrrrrrr) then pump the brake to get the pistons moving, repeat if necessary. You can remove the GT and brake fluid from the caliper prior to pad installation with a mixture of demineralised water and Isopropyl alcohol, don't use brake cleaner, it's sh1t.

    Premier Icon ahwiles
    Subscriber

    i use the following technique to get my avid brakes working like a charm:

    1) don't touch them until they're knackered (about 2 rides).

    2) dump them in the bin.

    3) replace with shimano deore/ lx/ slx.

    my 'avid' brakes now work very well thanks…

    (i arrived at this process after spending thousands of hours trying to force the pistons back in, so i could fit some new brake pads to a set of juicy 5's).

    anything that requires as much tlc as avid brakes is incompatible with having a life.

    Thanks ahwiles, I'll try those techniques tonight, can't phucking wait!

    P.S. It took THAT many rides?

    TandemJeremy
    Member

    GT 85 might damage the seals – cause them to swell and the pistons to stick. Use known safe lubes only.

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