wfo9 Posted February 24, 2014 Report Share Posted February 24, 2014 Hey guys, I'm new to trials and just purchased a 2010 290 access model. I think it is basically the same as a 2009/2008. Anyway, bike runs great and has been well maintained, but I'm having one problem with the bike. Obviously, trials is a slow speed sport, but I occasionally get up a little speed on the trail. I'm having an issue where my rear brake starts to drag really bad after building some speed. It seems to be heat related because once I stop and let it cool down it goes back to normal. At one point, the rear wheel was almost completely locked up. I'm going to try to bleed the rear brake and put in new fluid, but was wondering if anyone had any other thoughts on the cause of this type of problem. I'm not really using the rear brake much, but it seems to be building up heat anyway. It is as if the pads are not releasing enough and then the fluid (or possibly air) is expanding as it heats up causing an eventual lockup. Any help would be greatly appreciated. One other question. My hands are taking a beating and I would really like to convert over to fat bars. Any info on what parts I would need to convert over would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
zerorev3rev4 Posted February 24, 2014 Report Share Posted February 24, 2014 possible rear pistons sticking in calliper heat builds up making problem worse ,or are you catching pedal whilst riding ,,does wheel spin freely when cold? is there slack in the pin that operates the master cylinder ,is piston sticking inside master cylinder ,,air will not cause this ,, fat bars wont help your hands either ,it is poss more to do with the position of the bars try moving back and if your tall get some spacers to lift them up Quote Link to comment Share on other sites More sharing options...
wfo9 Posted February 25, 2014 Author Report Share Posted February 25, 2014 The pedal is not catching on anything and there is slack between the lever and the pin that goes up inside the master cylinder. I don't know how to tell if the piston in the master is sticking. The brake does work, but the pads seem to ride very close to the rotor, even when cold. The wheel pretty much spins freely when cold, but it is hard to tell with the chain drag if it is 100% free, but I would say free enough. I would need to get the chain off to verify what type of drag is there. I rode it again today and the same thing happen. I actually dumped water on it and that seemed to fix it for the time being, but I doubt that is a good solution. Although the pads ride close on my enduro bike, you can see the piston move when the brake is pressed. On the Sherco I really can’t see any movement although I can feel it squeezing the rotor. In general it looks like the caliper pistons are not going back in enough. This causes the roto to heat up and the problem just gets worse. I was thinking I could take the wheel off and push the pistons mostly out and then lubricate them and push them back in and see if that helps. I have had that technique work with hydraulic brakes on bicycles. Quote Link to comment Share on other sites More sharing options...
tony27 Posted February 25, 2014 Report Share Posted February 25, 2014 Could be that your pads are getting worn enough that the pistons are staying out too much. I wouldn't try pumping the pistons out to lubricate them as you're more likely to end up tipping them when trying to push them back The way to see if the piston in the master is sticking is to remove the lever & rubber boot then have a look to see whether the piston is in contact with the circlip at the base of the master cylinder, give the piston a couple of strokes with a screwdriver to make sure it returns freely Quote Link to comment Share on other sites More sharing options...
copemech Posted February 25, 2014 Report Share Posted February 25, 2014 (edited) Could be that your pads are getting worn enough that the pistons are staying out too much. I wouldn't try pumping the pistons out to lubricate them as you're more likely to end up tipping them when trying to push them back The way to see if the piston in the master is sticking is to remove the lever & rubber boot then have a look to see whether the piston is in contact with the circlip at the base of the master cylinder, give the piston a couple of strokes with a screwdriver to make sure it returns freely Add, get the boot off and inspect for a cut or small entry point of water if corroded/ dirty. I repack mine with selecone grease. The way to see if the MC is holding pressure is to crack the bleeder when dragging and hot to see if it relieves pressure. Edited February 25, 2014 by copemech Quote Link to comment Share on other sites More sharing options...
mokwepa Posted February 25, 2014 Report Share Posted February 25, 2014 Hi cope, ive been thinking of doing the same, shoving grease inside the boot. I did spray q20 (our version of wd40) I side the boot but then had a issue with the piston sticking so have left it dry. Would grease be a better option? Quote Link to comment Share on other sites More sharing options...
wfo9 Posted February 25, 2014 Author Report Share Posted February 25, 2014 Thanks for the suggestions guys. I will take it apart tonight and see where I can get with it. I already stripped most of the bike down last night. I can' get over how simple these are to work on. I'm assuming the master piston is going to look like it is sticking if the caliper pistons are sticking. You have to manually push the caliper pistons back in when changing pads, right? Quote Link to comment Share on other sites More sharing options...
tony27 Posted February 25, 2014 Report Share Posted February 25, 2014 Leave the pads in place & use 2 screwdrivers between them to force the pistons back, if they aren't too far out they should push back fairly easily without tipping in the bores Quote Link to comment Share on other sites More sharing options...
copemech Posted February 26, 2014 Report Share Posted February 26, 2014 Hi cope, ive been thinking of doing the same, shoving grease inside the boot. I did spray q20 (our version of wd40) I side the boot but then had a issue with the piston sticking so have left it dry. Would grease be a better option? Yes but you need to use the silicone pasty grease to be inert to the rubber! Quote Link to comment Share on other sites More sharing options...
wfo9 Posted February 26, 2014 Author Report Share Posted February 26, 2014 I think I fixed it. I have not ridden it yet, but it feels normal now. Still not sure what the exact issue was because I did a bunch of different things while trying to resolve it. I could not get both pistons to go back in in the caliper no matter what I tired. I could get one side to go at a time, but pushing on both would not budge. I finally resorted to bleeding some fluid out while pushing on them. That worked and everything functioned normally after that. It seemed like the system was overfilled with fluid, but it could have been something else. I lubricated all the pistons… It has a nice progressive feel now. Hopefully it won't drag after it gets heated up (raining here now). Quote Link to comment Share on other sites More sharing options...
copemech Posted February 28, 2014 Report Share Posted February 28, 2014 See how it does when hot, as the pistons are moving now that is a good thing. The problems come in when the fluid expands with normal heat from use and has nowhere to go if the MC piston is not returning fully to open the return port within. This happens in the last little bit of MC piston return travel and is regulated by internal spring unless blocked by debris or corrosion. Slack in pedal does not insure full piston return and a mm or two makes a difference. Quote Link to comment Share on other sites More sharing options...
wfo9 Posted March 1, 2014 Author Report Share Posted March 1, 2014 See how it does when hot, as the pistons are moving now that is a good thing. The problems come in when the fluid expands with normal heat from use and has nowhere to go if the MC piston is not returning fully to open the return port within. This happens in the last little bit of MC piston return travel and is regulated by internal spring unless blocked by debris or corrosion. Slack in pedal does not insure full piston return and a mm or two makes a difference. I think you hit the nail on the head. Went and test rode today and it locked up again when hot. I spent the entire evening troubleshooting it. Ended up taking the master cylinder apart. I could not even get compressed air to flow from the return port... It did however flow after I took out the spring and piston LOL. It all looks to be in good condition, but when put the piston back in with the c-clip in place it blocks the return/overflow port. It is as if the clip is to thick or something (maybe the previous owner installed the wrong one). Seems to work fine without the clip in as the piston moves down enough.. The spring is strong and I could not see any obvious debris or corrosion. Maybe a little on the piston head. Any ideas besides a new master? I was really looking forward to riding today and this weekend ;-( I considered grinding down the piston head a bit but I figured I would re-think tomorrow. Is that a crazy idea? Quote Link to comment Share on other sites More sharing options...
wfo9 Posted March 2, 2014 Author Report Share Posted March 2, 2014 OK, think we got it figured out. I won't be sure until I re-assemble and test it out, but it looks like the problem was the reservoir return port in the master cylinder being blocked by something. I could never really see it but I think it is a tiny rubber orifice of some sort. The guy I bought the bike from had a rebuild kit for the master, but the new piston, spring and c-clip did not help. So another guy was there (who is the local beta dealer with a lot of experience with trials bikes).and he used a jet cleaning needle (basically a really tiny drill bit) to open up the port. Now it seems to allow things to flow normally. Before it was opened up it allowed air to move without the piston in, but as soon as the piston was in the master it blocked it off just enough to not flow. Now it flows until the piston is pushed up above the c-clip position. . I won't declare victory until it survives a long ride. Quote Link to comment Share on other sites More sharing options...
copemech Posted March 2, 2014 Report Share Posted March 2, 2014 That should fix ya I would think! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.