speedysdad Posted September 20, 2014 Report Share Posted September 20, 2014 Hello gentleman, I am new to trials bikes as my son races woods on a KTM. He decided to get a trials bike for cross training for Endurocross. The bikes seem simple enough, I have read every post in this forum while working on an 05 TXT Pro (The clutch is much better now). Enough intro. Since we got it the rear brakes quit working. So last night I rebuilt the rear master cylinder. I bleed brakes, back bleed brakes, vaccum siphon, and bleed brakes again for three hours, nothing happens. It won't pull or push fluid. This morining I start again. I take the rear MC apart again and see inside the barrel that there is some discoloration, maybe corrosion. It seems smooth. Then I inspect the old plunger and seals and notice some discoloration on it also. The new plunger seems tight, but it will not pump up or push any significant amount of fluid. Does this means I need a new MC? Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 20, 2014 Report Share Posted September 20, 2014 (edited) So is the inlet port from the reservoir clear? You might need a new m/C, but more likely have a air pocket. I prefer just bleeding from the caliper. Get the rear caliper up higher than the m/c. Just use a 3ft piece of clear hose and drape over the rear fender. Straight up from the bleed nipple. Takes patience, but helps draw the air slowly out. Good luck. P. S. also try new brake pads. Most of the time it is just worn pads. Edited September 20, 2014 by lineaway Quote Link to comment Share on other sites More sharing options...
dadof2 Posted September 20, 2014 Report Share Posted September 20, 2014 Agree with lineaway, check the fill port(s) (about 0.5mm diameter) between the reservoir and the master cylinder a fully clear. Also check the master cylinder piston is returning fully to uncover the ports. I have know the piston not be able to return fully because of pedal adjustment or corrosion. You say the plunger seems tight, it should move fairly easily, with just light finger pressure once lubricated with brake fluid or red brake grease. Remove the seal from the piston and polish both the piston and bore with 1200 grade wet and dry until the piston (without seal moves effortlessly. Then pressure back bleed with the bike stood on its back wheel / front wheel raised onto a table. Quote Link to comment Share on other sites More sharing options...
speedysdad Posted September 20, 2014 Author Report Share Posted September 20, 2014 The inlet port is clear and I have good flow to the mc. I can't get fluid to pump out of the mc to the caliper. I can't get any push from the mc, It won't pump up or push enough fluid to push out the air in the line. I am using the clear hose. I discovered the lack of movement at the caliper while attempting to change the pads. I adjusted the pedal to have a little free play when I installed the new mc kit. When I said the plunger was tight I just meant snug like it was fitting correctly, not with any resistance. I have already tried the back bleed as you described when hours of standard bleeding didn't work. Thats why I came here for advice. I am not new to brake rebuilding, but I have hit a wall with this one. Never seen a system that won't build pressure at all. After pumping the pedal 50 times, from fully up to fully down, I might get the bleeder to spit out a single tiny bubble. The mc hasn't built the slightest bit of resistance since I started. Now very frustrated. Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 20, 2014 Report Share Posted September 20, 2014 Have you tried removing the brake pedal and just use a Phillips screwdriver to get maximum movement. Quote Link to comment Share on other sites More sharing options...
speedysdad Posted September 21, 2014 Author Report Share Posted September 21, 2014 Kind of, I used an allen wrench Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 21, 2014 Report Share Posted September 21, 2014 (edited) You said you used a clear hose, length and going up vertical is important. I use a totally different method than most. Mine usually works pretty fast. Recently I had a Beta zero that took like a week to bleed. It had sat in a barn for 18-20 years. Was a pain in my ass. But I got it with no parts used. 15-20 minutes every evening with the rear caliper hung in the air. Good luck! Edited September 21, 2014 by lineaway Quote Link to comment Share on other sites More sharing options...
speedysdad Posted September 21, 2014 Author Report Share Posted September 21, 2014 You said you used a clear hose, length and going up vertical is important. I use a totally different method than most. Mine usually works pretty fast. Recently I had a Beta zero that took like a week to bleed. It had sat in a barn for 18-20 years. Was a pain in my ass. But I got it with no parts used. 15-20 minutes every evening with the rear caliper hung in the air. Good luck! Hey thanks, that gives me hope Quote Link to comment Share on other sites More sharing options...
zippy Posted September 21, 2014 Report Share Posted September 21, 2014 I had issues with my 2003 GasGas rear brake. Just lost rear brake all of a sudden. Rebuild master cylinder and all was good for a while, then lost rear brake. I ended up buying a new rear master cylinder. The bore was worn enough to cause problems. Also try raising the front of the bike and bleed the master cylinder at the banjo bolt the attaches the rear brake line to the master cylinder. There is a spot where air can get trapped at the top of the master cylinder Quote Link to comment Share on other sites More sharing options...
richt Posted September 21, 2014 Report Share Posted September 21, 2014 I bet there is air in the banjo bolt at the top of the MC. I take the MC off the frame and invert it then operate it with a piece of rod the full travel and use a syringe at the same time connected to the reservoir hose. It's an orrid job, usually for me it will suddenly start to work followed with a sigh of joy Quote Link to comment Share on other sites More sharing options...
speedysdad Posted September 21, 2014 Author Report Share Posted September 21, 2014 I bet there is air in the banjo bolt at the top of the MC. I take the MC off the frame and invert it then operate it with a piece of rod the full travel and use a syringe at the same time connected to the reservoir hose. It's an orrid job, usually for me it will suddenly start to work followed with a sigh of joy This sounds promising. Thanks everyone for all the suggestions. Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 21, 2014 Report Share Posted September 21, 2014 Richt has a great idea. Too bad the line runs through the swing arm, so you could do this with the whole system at once. I actually just had to do this with my son`s hydraulic clutch on his truck. The only way to bleed it was to remove the whole thing from the vehicle. Quote Link to comment Share on other sites More sharing options...
jfc Posted September 21, 2014 Report Share Posted September 21, 2014 Have you burped the banjo on the m/c, I had the same thing happen, I could not move any fluid and then I burped the banjo and after that was able to bleed the brake line in the normal way. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted September 21, 2014 Report Share Posted September 21, 2014 One one occasion when a GG owner had the same problem as you it turned out to be the bleed nipple not seating properly, it was drawing in a hint of air each time the pedal was released. Sometimes I have known a system fail to bleed, giving same symptoms as yours when slave cylinder pistons were just flexing back and forth on their seals. Wedging the pistons fully back during reverse bleeding sorted this. What do you feel if you put your finger over MC outlet port and work pedal? Sometimes I have know people reverse bleed with 20ml syringes with no result, give it a fast flush with a 100ml syringe and its cured. Quote Link to comment Share on other sites More sharing options...
eddie1 Posted September 22, 2014 Report Share Posted September 22, 2014 I'll add my experience as it ,may help you. To cut it short it was wear in the slave/master cylinder seal. When I changed the rear suspension bearings I kept the whole rear brake system complete as I had had trouble in the past trying to bleed the system. A couple of rides later I lost all rear brake. I checked for leaks and found none so suspected that air must have got in the system even though it had not been apart. I started by disconnecting the brake rod to make sure that the piston was not restricted. Used a syringe to push fluid first from the res pipe through to the caliper bleed nipple. NOK Again used the syringe to push fluid from the bleed nipple back to the res. NOK Pumping the lever gave nothing and I also noted no fluid flow. I had previously bought a master cylinder repair kit for another bike only to find it was a bleed problem so was reluctant to go down the same route. I lifted the rear wheel up above the handle bars and tried again syringing fluid from the res first and the bleed nipple next thinking I had got some pedal only to find it disappear after two pumps. By accident I pushed fluid through from the bleed nipple with the cap still on the res and found there was a slight brake right at the bottom of the pedal stroke. Thinking it would get better I took it for a bit of a practice. It didn't get any better or worse and was not quite enough to lock the wheel on a steep hill. By now I had ordered a master cylinder repair kit but carried on trying to bleed it in the mean time. Looking at the system I suspected that a possible place for air to get trapped was at the cylinder where fluid entered lower than the banjo bolt. I thought I was on to something when I unfastened the cylinder from the frame and turned it upside down before bleeding. Again I had something only to lose it after a couple of pedal strokes. Next day the repair kit turned up. I fitted the kit, pushed fluid from the caliper to the banjo bolt,filled the cylinder as best I could, connected the res, pushed fluid from the bleed nipple to the res with the cylinder upside down. Bingo Job done best rear brake I have had since I bough the bike. good luck Quote Link to comment Share on other sites More sharing options...
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