jimbob001 Posted August 19, 2008 Share Posted August 19, 2008 Hi People, Having purchased a new set of USED front calipers I am having trouble bleeding them. Is it possible that they could draw air back through the piston seals whilst bleeding? Air just keeps coming and there doesn't appear to be any leaks from the pipes. Checked everthing several times etc.... Just getting a little fed up now, Anyones help would be really great Thanks Jim Link to comment Share on other sites More sharing options...
grizzlydan Posted August 19, 2008 Share Posted August 19, 2008 Because they were 2nd hand you may still need 2 replace the seals on the calipers, depends on how long they sat on the suppliers shelf. What was wrong with the original calipers? Just wondering coz they may have just needed piston & seal replacement kits fitted. Link to comment Share on other sites More sharing options...
fosdyke Posted August 20, 2008 Share Posted August 20, 2008 Because they were 2nd hand you may still need 2 replace the seals on the calipers, depends on how long they sat on the suppliers shelf. What was wrong with the original calipers? Just wondering coz they may have just needed piston & seal replacement kits fitted. Quite right - you should dismantle and rebuild the calipers to be sure. However sometimes you can get away with it if the calipers haven't sat for a while, and it is more likely that if the piston seals had gone they would pee brake fluid out - which you don't want to happen as apart from having to replace your pads you are likely to run into a tree or worse! As to the air you need to bleed through at least 2 full reservoirs of brake fluid making sure you don't let it run dry (you will just suck more air in), to be sure you have got all the air out. If this doesn't work I would suggest you may be pulling air in from the the reservoir end of the brake system. Let us know how you get on. Link to comment Share on other sites More sharing options...
jimbob001 Posted August 20, 2008 Author Share Posted August 20, 2008 Quite right - you should dismantle and rebuild the calipers to be sure. However sometimes you can get away with it if the calipers haven't sat for a while, and it is more likely that if the piston seals had gone they would pee brake fluid out - which you don't want to happen as apart from having to replace your pads you are likely to run into a tree or worse! As to the air you need to bleed through at least 2 full reservoirs of brake fluid making sure you don't let it run dry (you will just suck more air in), to be sure you have got all the air out. If this doesn't work I would suggest you may be pulling air in from the the reservoir end of the brake system. Let us know how you get on. Put at least 3 reservoirs of fluid through but still get air bubbles! Defo not sucking air in from master cyclinder or reservoir have always kept it topped up. Spoke to a motorcycle mechanic today and he said that I need to "kick start" the bleeding by using a syringe through the bleed nipples on the calipers to fill them with fluid, kind of back bleeding Gona give this a try and will let you know. As for the need for replacement calipers, failed MOT with binding brakes, My mate backed off the pistons in the calipers and we couldnt get them to move again, Im told that to remove seized pistons from calipers you are to use compressed air, dont have a rig set up for this. Was quoted bout £130.00 from bike shop for refurb, thought it would be more cost effective to but another set from ebay, (they came with 30 day warranty) P.S Does anybody recommend a power commander for my R6 5sl, this is the 1st fuel injected bike i have had, and i thought the throttle response would be nice and smooth, though I have found it to be a bit snatchy etc round town and at low revs. Im just getting back into riding again, and would appreciate the feedback on the fuel injection! Thanks people , P.P.S is there anybody around my neck of the woods out there, im from leyland near preston? Jim Link to comment Share on other sites More sharing options...
fosdyke Posted August 20, 2008 Share Posted August 20, 2008 Put at least 3 reservoirs of fluid through but still get air bubbles! Defo not sucking air in from master cyclinder or reservoir have always kept it topped up. Spoke to a motorcycle mechanic today and he said that I need to "kick start" the bleeding by using a syringe through the bleed nipples on the calipers to fill them with fluid, kind of back bleeding Gona give this a try and will let you know. As for the need for replacement calipers, failed MOT with binding brakes, My mate backed off the pistons in the calipers and we couldnt get them to move again, Im told that to remove seized pistons from calipers you are to use compressed air, dont have a rig set up for this. Was quoted bout £130.00 from bike shop for refurb, thought it would be more cost effective to but another set from ebay, (they came with 30 day warranty) Jim Think you need to do a complete dismantle and reassemble with a rebuild kit. if you haven't got compressed air try forcing the pistons out using the brake system: You will need to remove the wheel, and get a container and rags to catch the spilt fluid. Pump out the pistons by using the brake (you may need to add more fluid), without the disc to stop them they should come out under the pressure of the fluid. Once they are out you will need to replace the piston seals before you reassemble, and I would recommend using a bit of clean brake fluid in the cylinders before replacing the pistons. As for the air bubbles rebuild the caliper first then try again. Link to comment Share on other sites More sharing options...
tobster Posted September 1, 2008 Share Posted September 1, 2008 Put at least 3 reservoirs of fluid through but still get air bubbles! Defo not sucking air in from master cyclinder or reservoir have always kept it topped up. Spoke to a motorcycle mechanic today and he said that I need to "kick start" the bleeding by using a syringe through the bleed nipples on the calipers to fill them with fluid, kind of back bleeding Gona give this a try and will let you know. Your mechanic friend is indeed correct. Bleeding brakes with large amounts of air is often easier/more successful if you backbleed. Fill a syringe (50ml) with brake fluid, attach it to the brake bleed niplle with some tubing, empty the brake reservoir, open the bleed nipple and slowly squeeze the syringe. the air will be forced out of the caliper, up the brake line to the reservoir. At worst this will get the bleeding process going and you can bleed in the more conventional method (that you're currently trying). Before you do that, check how firm your brake lever is, as this method should be good enough on its own. I don't think you need to take pistons out etc. Also not being patronising, but I would suggest that if you don't know how to bleed brakes (beyond the standard method) then you should NOT be taking the calipers apart (at least without expert suspervision) - after all, they are kind of important... Good luck Link to comment Share on other sites More sharing options...
Moderator drewpy Posted September 1, 2008 Moderator Share Posted September 1, 2008 sometimes when you are bleeding brakes, the fluid just pushes out and then pulls back in. try getting an assistant to lock off the bleed valve when the lever is pulled in. also tying the brake lever overnight lets the air rise into the resevoir. BTW is the splurge hole unblocked as this prevents the fluid return and causes brakes to stick. My complete method is what chris pearson does (CMM) run a tube from the bleed nipple and wire it into the resevoir then the fliud has a return circuit and is very effective as no air can re-enter the system and any air left, can rise to the resevoir. Link to comment Share on other sites More sharing options...
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