thesaint Posted October 3, 2018 Report Share Posted October 3, 2018 I am trying to bleed the rear brakes on one of my trial bikes a 2005 Gas Gas TXT 125 Pro I just found out that trying to bleed the rear brake is not an easy job. I have changed the rear barke caliper with a new one since the bleed screw was broken when i bought the bike I have also replaced the rear brake reservoir with a new original one since i managed to ruin the rubber gasket/seal on the old rear brake reservoir First i tried by filling up the rear brake reservoir with brake fluid and push the brake lever but it seems that no brake fluid is coming into the brake pump. I have also tried to backbleed the rear brakes using a large syringe and push the brake fluid thru the bleed screw when i had loosen it a little but that did not work and it just made a mess with brake fluid on the floor. Next i was thinking of taking off the brake line that goes into the brake pump on the underside and try to use the syringe to get some brake fluid into the brake pump. Any of my fellow members here on the forum have any ideas on how to do this the easy way? . Quote Link to comment Share on other sites More sharing options...
section swept Posted October 3, 2018 Report Share Posted October 3, 2018 Make sure that the feed hose from master cylinder to caliper is not blocked, crushed or bent too tightly. With bike upright and reservoir cover off pour in a quantity of brake fluid...what type are you using?...open the caliper bleed nipple a few turns and sit and wait about 5 minutes. You should see a small weepage from the bleed nipple. If you do a search on this site the rest of the info and techniques are there for you to try. Quote Link to comment Share on other sites More sharing options...
thesaint Posted October 3, 2018 Author Report Share Posted October 3, 2018 (edited) Forgot to write it the first post that the bike have been sitting for a few months without any rear brake caliper all of the brake fluid is drained out. I am using DOT 4 brake fluid as it says on the cap for both the front and rear brake Thinking of raiseing the bake so much that the front wheel is standing up against the wall? I will try that I will have a close look on the brake hose where it attaches to the brake pump Just googled tand found the below answer where it says to use a empty syrringe to create vacuum from the rear caliper, What is written below is about Gas Gas rear brakes from this forum as well Fill the reservoir, then putting the empty syringe on the bleed nipple and as you pump the break lever start to pull the syringe creating a vacuum and when you get to the end of the syringe lock the nipple and repeat process, Edited October 3, 2018 by thesaint Quote Link to comment Share on other sites More sharing options...
d2w Posted October 3, 2018 Report Share Posted October 3, 2018 (edited) An even easier procedure is to fill the syringe with brake fluid and inject it into the rear brake bleeder nipple. This will force the fluid through the entire system. The fluid will then accumulate in the reservoir. Note that if you can't force fluid into the system it may be due to there not being sufficient flee play in the pedal/master cylinder; there's a hole to the reservoir which is exposed when the pedal is at rest and this allows the circuit to refill. When you apply force to the pedal the piston moves and covers the hole and pressurizes the fluid which causes the slave pistons to expand and apply the brakes. Sorry ... I just reread your original post and you mention that you tried to backbleed the system but it didn't work. It sounds like your return path to the reservoir is blocked. Again, check for the freeplay in the pedal/master cylinder. Edited October 3, 2018 by d2w Quote Link to comment Share on other sites More sharing options...
cleanorbust Posted October 3, 2018 Report Share Posted October 3, 2018 I've been through this process too and taken account of the advice points given in this thread, with little success. What eventually made the difference for me was using a brand new large syringe, providing more force in pushing brake fluid through the system (from the rear caliper towards the reservoir). This seemed to eliminate the nooks and crannies where air had been trapped. Quote Link to comment Share on other sites More sharing options...
digger144 Posted October 3, 2018 Report Share Posted October 3, 2018 just remove caliper from the bike, hold it higher than the master cylinder, best remove brake pedal, use a screwdriver to make sure you get a full stroke of the piston in the master cylinder, bleed in the normal manner 1 Quote Link to comment Share on other sites More sharing options...
section swept Posted October 3, 2018 Report Share Posted October 3, 2018 Get those pads forced back as far as they will go. Use suitable spacers to keep them there. The lost motion as the pistons dither about back and forth minutely prevents the bleeding process from being completed. With the pistons forced back and held there by the spacers now feel the brake pedal for lost motion or free play, try to adjust this out so that as soon as you move the brake pedal the master cylinder piston moves as well. Fill the reservoir with fluid and with a clear tube on the bleed nipple and a ring spanner or suitable spanner on the nipplejust open it a quarter turn, immerse the tube in a jar of brake fluid ( just enough to allow the tube to sit in) push the brake pedal down and watch the fluid move through the clear tube, if it doesnt then try operating the pedal quite quickly a few pumps. When the pedal is down as far as it will go close the nipple, let the pedal return slowly, ensure the reservoir is kept topped up. Repeat until no air bubbles are seen coming from the clear tube. If that doesn’t work you will need to either force the fluid through from the master cylinder end, or draw it through from the caliper. All suggested before and all usually work. You will get there in the end it’s just a matter of determination and process. The factory method usually consists of pressuring the master cylinder reservoir and forcing fluid through and then tightening the nipple. Take care as you probably know brake fluid is harmful to painted surfaces, dont shake the fluid container asthis airates the fluid, some types are hygroscopic...absorbing moisture from the atmosphere, so keep the container sealed tightly. Quote Link to comment Share on other sites More sharing options...
d2w Posted October 3, 2018 Report Share Posted October 3, 2018 (edited) A slight - but related - diversion ... on two occasions I've snapped a seized brake bleeder nipple The nipple is hollow and I'm guessing the dissimilar metals of the nipple and caliper set up some sort of galvanic reaction and/or oxidization which effectively glues the two parts together. I tried to use heat to free them first but it never worked. But once broken off I was able to carefully use a hand drill to remove the broken bits and retap using an M6x1 (I think). So long as you don't go too deep on the final/largest drill bit you can preserve the seating surface and the new nipple will seal. I then use some Teflon "plumber tape" on the threads to better secure the nipple and ensure easy removal the next time. Don't forget to pierce a hole in the tape to allow the fluid to drain when the nipple is partially backed out. Edited October 3, 2018 by d2w Quote Link to comment Share on other sites More sharing options...
taffe Posted October 3, 2018 Report Share Posted October 3, 2018 Hi, took me a long time too recently, I had done all of the above but did two extra things. I sucked the fluid through from the nipple end (with a syringe ang saw minute bubbles coming, left nipple open overnight with hose hanging down, syringe still attached. At least had some pedal pressure after that. Then went for a ride and after awhile the brake started working fine. Then I took the hose off of the car exhaust and removed the car from the garage, screwed up the note, and alls well.? Taff Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 3, 2018 Report Share Posted October 3, 2018 You have tried new pads? Quote Link to comment Share on other sites More sharing options...
thesaint Posted October 4, 2018 Author Report Share Posted October 4, 2018 The rear brake caliper is a brand new one 100 percent identical to the old one The rear brake pads are brand new I went out and bought a brake bleeder that i hook up to my air compressor and build up some air pressure ( see the attached picture) and you put the black end on the bleed nipple on the rear caliper after you have opened the bleed nipple a little and pull the lever on the brake bleeder and the the brake fluid is supposed to be pulled thru the bake system because of vacuum. Not even this worked. I think i will try to replace the brake line that goes from the brake reservoir to the brake pump and the i will fill the syringe with brake fluid and try to get some brake fluid into the brake pump. I will off course take off the brake pump Quote Link to comment Share on other sites More sharing options...
d2w Posted October 4, 2018 Report Share Posted October 4, 2018 Well, there's only four major components in the system; the rear brake caliper/slave cylinder, the hose, the master cylinder, and the reservoir. As you speculate, there must be a blockage in at least one of those items. Time to dismantle and test each for flow. My money is on a stuck piston in the master cylinder (or one that;s not retracting sufficiently to expose the refill hole). Good luck and keep us informed of your findings. Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 4, 2018 Report Share Posted October 4, 2018 All you need is 3 feet of clear hose. Make sure it is securly on the nipple. Run tbe hose straight up and over the rear fender. Remove your brake pedal, so you can pump the master cylinder with a phillips screw driver. Doing this allows a full stroke the piston and allows it to fully return. Open up the nipple pump till the fluid risez steadily to the fender. (keep the fluid full) If you do not get any movement, try burping the hose fitting at the M/C. Just a little turn of the wrench to make sure fluid is coming out. By the time the fluid reaches the rear fender, most of the air bubbles should be coming out. Of course you can close tbe nipple any time and see if you are building pressure. The correct way would be to take the whole system off and hang the caliper above the m/c and bleed it. But since your brake line goes through the swingarm this would not work. Quote Link to comment Share on other sites More sharing options...
thesaint Posted October 5, 2018 Author Report Share Posted October 5, 2018 (edited) Just took the brake pump off of the bike and also took off the brake fluid hose that comes from the rervoir Then i used the syringe to press quite a bit of brake fluid into the brake pump while i also used the brake bleed that use vacuum I managed to get all of the brake fluid i wanted into the brake pump doing this The only thing is that is different is that i turned the brake fluid inlet on the brake pump (where the brake fluid hose from the reservoir goes) to point up whil i filled it using the syringe. The normal postition for the brake fluid inlet on the brake pump is that it points down since the hose for the brake reservoir goes under the engine and so up and into the brake pump Edited October 5, 2018 by thesaint Quote Link to comment Share on other sites More sharing options...
thesaint Posted October 8, 2018 Author Report Share Posted October 8, 2018 (edited) Forgot to update this thread I have finally bleed the rear brakes on the bike This is how i did it I took off the rear brake pump and used a large syringe with a 1 inch lo hose on the and then filled the syringe with brake fluid and attched it to the rear brake pump (was careful so there was almost no air in the large syringe) While i used vacuum and bleed the rear brake caliper i pressed brake fluid in the large syringe into the rear brake pump until i saw there was no more air and then i closed the bleed nipple on the caliper I already had brake fluid in the brake fluid reservoir which i had plugged using a screw. When i.took off the latge syringe on the brake pump i did my best to to quickly get the brake hose from he brake fluid reservoir on to the brake pump This so i would get as little air as possible in the system After i had done this i topped up the brake fluid reservoir and and bleed the rear brake caliper using vacuum Doing it like this the job with bleeding the rear brake caliper worked like a charm and it took me about 30 minutes But jeez so much trying this and that to get this little job done.... Edited October 8, 2018 by thesaint Quote Link to comment Share on other sites More sharing options...
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