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Will removing brake fluid allow caliper pistons to retreat easily?

Discussion in 'Technical and Troubleshooting Torque' started by jaguarfanster, Jun 23, 2012.

  1. I've been searching everywhere for this, but cannot seem to find an answer. Having removed the old (and worn out) brake pads, the calipers are almost fully extended. They are quite hard to push back, and I do not want to risk damaging the disc. As the pressure of these pistons relates to the brake fluid, will extracting the fluid allow for an easy retreat? If not what is the best way to get these pistons back home, without having to remove the wheel, or caliper assembly. Thanks :)

  2. First of all, DO NOT put anything between the disc and piston to push it back, like a screwdriver, you risk warping the disc. Removing the brake fluid is not necessary, it just creates more work in that you have to bleed the hydraulic system, saying that, if it hasn't been replaced in the last 2 years, now would be an ideal time to put new brake fluid in.

    There's little chance you'll push the piston in with your thumbs (although I have done it on the rare occasion) try using a "G" clamp on the back of the caliper and wind the piston in slowly, making sure you're not squirting fluid out of the master cylinder (don't get it on paint and wash it off pronto if it does).

    Obviously, you need to be able to swing the caliper off its mount to do this, you should only need to remove one mounting bolt, 2 if necessary.

    After fitting new pads, be sure to carefully and slowly pump the lever to bring the pads toward the disc, until the lever is firm again, if you forget this, the first time you apply the brakes, you're not going to stop!! Be careful,

    • Like Like x 1
  3. simple answer no...

    open the bleed nipple if its too tough. bleed after.

    don't allow the fluid to run dry in the MC, certainly don't

    you'll have to take the caliper off... how did you think you'd be able to fit fatter pads with the pistons out and everything in situ?
  4. eh?

    take the lid off the master cylinder

    the fluid will flow back to the cylinder easily as the pistons in the caliper are pushed back.

    wrap a piece of cloth around the cylinder in case the reservior overlfows
  5. OK, so I understand that making the system dry is a no-no. Furthermore I think ill remove the cap on the master cylinder (no negative pressure etc, seems reasonable). I don't quite want to remove the front wheel, as I'll be changing rear pads as well (rear wheel doesn't look fun to take off). So I'll give 'swinging the caliper' off a try. Thanks guys, for the advice. Saved me unnecessary work :)
  6. Take caliper or the wheel off, which ever is easier, before removing the old pads, jam a screw driver in there and lever the pads appart (you're tossing the pads anyway!).. The other way is to rock the caliper side to side as you remove it from the disc, same result, you are levering the pads appart leaving you with more room for the new pads..
  7. I ended up taking off the caliper completely. Found this to be much easier in accessing the pistons, than "swinging it off". The rim makes for a tricky position to work with, but that isn't an issue with a free caliper. Unfortunately I don't have access to a g-clamp, but the pistons do move millimeters with thumb pressure. My thumbs are pretty aesthetic now. Hercules could have owned a similar pair :p.

    I didn't try the brake pad leveraging method, although I have heard it mentioned more than once. Just seem's easier to pressure press the pistons down with a g-clamp.
  8. last time i used a hammer and a sparkplug tool..... it worked
    • Like Like x 1
  9. You must have excellent coordination :)
  10. Just take a little bit of oil out of the Master Cylinder, as you push the pistons back in, it might overflow if you dont,
    An absorbent paper towel over the master cylinders stops it squirting every where,
    You do need to take the Covers off the M/C's to allow the oil to go back easily,
  11. Interesting replies
    Best one is open caliper bleeder.
    crap built up in lowest point
    Is not forced back to master.
  12. You don't say what you ride...or how old it is.
    If your bike is over two years old get rid of the old brake fluid while you are there.
    And so the brakes work to their best get a can of brake clean and go over them properly.
    Best bet is to take the caliper block down to the servo and blow it out with air first. If you don't have a compressor at home.
    Give your wheel bearings a little love and some decent grease.
    And clean the axle off before you stuff it back in. Dirt on the thread will cross thread it pretty easy. Nothing worse for mine and a pet hate.
  13. I ended up forcing the pistons back in with a g-clamp, and replaced the old pads with the new. When pumping the brakes to get the pistons to mate with the new pads I noticed that the brake pressure had drastically reduced. I'd say to about 40% of the original.

    Could I assume that air has entered the system now? Furthermore, I may have made a silly mistake in the installation process. When the old pads were out I think I accidentally pumped the front brake a little much, resulting in one piston slightly coming out of its seat. Also I did notice that one of my two pistons does not extend after brake pumping. However when I apply g-clamp force to the easily movable pistons, this stuck piston does move after brake pumping. Could this be a result of dirt/crap stuck in the pathway to this piston? Do I have to take apart the entire caliper, and clean out passageways, or can I get away with a brake bleed.

    For the record my motorcycle is a Honda Spada. Apologies for not mentioning that earlier. Also where exactly is the bleeder screw on these calipers? Can't find a mention of it in the manual.
  14. You shouldn't have needed to pump the brakes with the pads removed and I'm assuming it leaked fluid out of the one where the piston came out slightly when you did. Once the piston is pushed back in straight and all the way home, if you then pump the lever, the piston with the least resistance will move, it's unlikely they both will move at the same time.

    Push both pistons back home, fit pads, caliper on bike, carefully and slowly pump lever to bring pads to disc. If spongy lever there's a good chance you need to bleed the caliper. Fill master cylinder with fluid, open bleeder nipple on caliper and it may gravity bleed. Nipple could be 8 or 10mm? on top of caliper, some clear hose pointing down to drain will let you see when there's NO bubbles and system is free of air. Remember to keep master cylinder fluid topped up. If it won't gravity bleed, pump lever few times and hold it in, open bleeder for say, 2 or 3 seconds, close bleeder then repeat. Do this until only fluid comes out. When only fluid comes out, hold the lever in, tighten bleeder, then release lever, check level of fluid in master cylinder and top up to full mark.

    Hope I haven't confused you, congrat's on giving it a go yourself, but take care,

  15. "Shouldn't have pumped the brakes with pads removed". In hindsight I completely agree with you Ned. Haha, I don't know why I did it. Perhaps curiosity got the better of me. Also knowing my pistons aren't malfunctioning is definitely relieving.

    I think I understand the steps you've provided. I'm quite glad they support the information provided on this lady's site, (http://www.bluepoof.com/motorcycles/howto/svs_bleeding_brakes/). Pictures are indeed helpful!

    Many thanks for the advice, Ned. Being a uni student, doesn't give me much in the way of funds to play with. Therefore whatever problems I encounter, I usually have no choice but to figure it out myself. However that isn't as bad as it sounds. The skills I've gained could have never been acquired through a textbook. It may take days but it's worth it. Although sometimes I fail miserably. That's when Sis at S Jay motorcycles really comes in handy!
  16. Did u get it sorted?
    There is an alternative bleed method that will help if needed
    Post if needed
  17. 11.22pm and finally I HAVE FINISHED! Well in a nutshell this is what happened. First I changed the pads out, and g-clamped the pistons back home. However I had about 30-40% of max braking efficiency on testing. The pressure in the system had disappeared.

    Subsequently I ended up draining the brake lines, and refilled with DOT4 fluid. The bleed method discussed above was used, until air bubble flow ceased. However the braking efficiency had now dropped to 20%. I checked for leaks, and didn't find any. I was quite frustrated at this stage. However I realised I hadn't reassembled the master cylinder cap. Considering this could possibly be the source pressure loss, the cap was fitted.

    I pumped the pistons back out (whilst the caliper was off the wheel) and added brake fluid to level in the MC. Using a g-clamp I began to push the pistons in one at a time. I stopped when pushing one piston in, generated enough pressure to push the other out. At this point I slowly opened the bleeder valve to allow for pressure release. Note that the master cylinder was sealed during this process.

    Again I tried a g-clamp to push the pistons in, stopping when the other started moving out. Once more the bleeder valve was slightly opened to allow for pressure escape.

    Eventually I had released enough pressure to get the pistons back home. However the brake pressure in the system was always at its peak. This was because I was basically, 'skimming' pressure off the top, using the bleeder valve.

    Finally I reassembled the caliper, and pads onto the front forks. Pumped the front brake a few times and voila. A well weighted (and definitely not limp) brake lever. I'd have to say the braking pressure and power is at least 20% more than before. Even greater than when I first purchased the bike.

    I'll have to repeat this on the rear brake now. It's always been floppy, I'll see if it gets any better this way.
  18. for anyone a note
    don't press the brake when the calliper is off, this will hyper extend it, hope that’s not what you've done, if so open the bleed valve and the brake fluid line then block the line in, make sure your reservoir is topped up, remove the rest of fluid from the cylinder, , make sure its all clean, you can clean with Metho, put it all back with springs rubber boot in place, connect fluid line till you see fluid coming out the bleed valve, then close the nut.
    You will then need to bleed your system , connect a small hose to the bleed valve and put it in a bottle with brake fluid, dot 3 or 4 what ever yours takes. press the brake while holding down release the bleed valve slightly and see if any bubbles are forming at the bottom of bottle with fluid. If so close valve release brake and do it over and over again till bubbles are gone.
  19. I did that by mistake at first, but then found that I had to in order to get any pressure at the pedal/lever. I.e. pumping the piston out (not completely out obviously), fill fluid in reservoir cap tightly, bleed, push piston back in, pressure builds up in the master cylinder, and VERY firm brakes result.