hoggyf Posted March 27, 2011 Report Share Posted March 27, 2011 Need some help chaps Front brake on my JTX250 is a bit spongy so tried to bleed it with no real improvement, during which I noticed that there appeared to be a weep showing, on the "bridge" of the caliper, i.e. on the top section where the caliper joins together (AJP 2 pot) when you squeeze the brake on hard. So new seal kit installed with new pistons and 'o' ring that joins the caliper sides together. Cleaned everything with brake cleaner then new fluid and bled up form the bottom up using a large syringe - no air present but there is still a sign of moisture on the joint on the top of the caliper when you squeeze on the brake. Its still no better in that the lever feels spongy generally and the stopping power is very poor, you certainly couldn't get the back wheel up in the air (not that I could anyway!!) So - any suggestions?? Quote Link to comment Share on other sites More sharing options...
jse Posted March 29, 2011 Report Share Posted March 29, 2011 Need some help chaps Front brake on my JTX250 is a bit spongy so tried to bleed it with no real improvement, during which I noticed that there appeared to be a weep showing, on the "bridge" of the caliper, i.e. on the top section where the caliper joins together (AJP 2 pot) when you squeeze the brake on hard. So new seal kit installed with new pistons and 'o' ring that joins the caliper sides together. Cleaned everything with brake cleaner then new fluid and bled up form the bottom up using a large syringe - no air present but there is still a sign of moisture on the joint on the top of the caliper when you squeeze on the brake. Its still no better in that the lever feels spongy generally and the stopping power is very poor, you certainly couldn't get the back wheel up in the air (not that I could anyway!!) So - any suggestions?? One of the things we did to those to make them work better was to take the caliper apart and use a surface plate (or thick piece of glass) and some 220 grit sandpaper to get the sealing surfaces straight, otherwise they were prone to flex. Jon Quote Link to comment Share on other sites More sharing options...
hoggyf Posted March 29, 2011 Author Report Share Posted March 29, 2011 Ok Jon at least I know its a known problem know, I take it then just lay a fresh piece of sand paper on the glass and take each side of the caliper and smoothly move across until i get a "witness mark" right across the full caliper then do the other side to match? Does that sound right? I've heard of this before but never tried it, does it need anything on the sandpaper i.e water? like doing car bodywork? thanks for the help Jon Quote Link to comment Share on other sites More sharing options...
jse Posted March 29, 2011 Report Share Posted March 29, 2011 Ok Jon at least I know its a known problem know, I take it then just lay a fresh piece of sand paper on the glass and take each side of the caliper and smoothly move across until i get a "witness mark" right across the full caliper then do the other side to match? Does that sound right? I've heard of this before but never tried it, does it need anything on the sandpaper i.e water? like doing car bodywork? thanks for the help Jon Jon, That's the way to do it. I sometimes use water or WD40 as it cuts a little faster. Use a light pressure, "figure 8" motion as it helps to avoid too much pressure on one side, resulting in a "wedge shaped" piece. Jon Quote Link to comment Share on other sites More sharing options...
legionnair Posted April 2, 2011 Report Share Posted April 2, 2011 Figure 8 pattern and rotate the piece a quarter turn every 5-8 figure 8's. This keeps the pressure point even around the entire piece Good Luck Dustin Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 5, 2011 Author Report Share Posted April 5, 2011 Possibly gonna go to plan B anyone know if a TXT 4 pot caliper will fit or failing that anybody got the measurements for the caliper mounts to see if they match? Having used the bike this weekend the caliper flex is quite large and facing it up may improve but can't see it will sort it where as I think the 4 pot si a better design. Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 7, 2011 Author Report Share Posted April 7, 2011 Well tried facing up the original caliper and rebuilding and whilst its marginally better it still flexes and with screwing the adjuster in further & further at the master cylinder, theres now a "squishing noise" at the master cylinder and i think a seal has gone on that now - Arghhhhh. Could still do with someone measuring the bolt centres on a TXT or Pro 4 pot caliper please. Hoggy Quote Link to comment Share on other sites More sharing options...
jse Posted April 8, 2011 Report Share Posted April 8, 2011 Could still do with someone measuring the bolt centres on a TXT or Pro 4 pot caliper please. Hoggy Bolt centers are 60mm+- on 02' with GG forks. Jon Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 25, 2011 Author Report Share Posted April 25, 2011 Still having problems, I stripped the piston out the master cylinder and found no damage, re-installed and adjusted the lever out which gives better braking but its still "soft" and after facing up the caliper and replacing the seals, pistons and seal o-ring, there is still some sign of flex in the caliper. What do i do next as on long downhills, I'm running out of brake. Do I fit a 4 pot, or does anyone have any better advice on what might be the problem. Just thought it already has braided hoses so they shouldn't be the problem. Quote Link to comment Share on other sites More sharing options...
jse Posted April 25, 2011 Report Share Posted April 25, 2011 Do I fit a 4 pot, or does anyone have any better advice on what might be the problem. I'm not sure what your final citeria is, but you may be expecting a bit too much from a 14+ year old system. If you want to have it perform as good as a new design, you may have to switch to the new design. You could try different pad compounds as a last resort. Jon Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 26, 2011 Author Report Share Posted April 26, 2011 I don't think that its an underlying design fault as at one time they'd be the best available but other bikes older than this that I've had previously (admittedly not trials bike) have still had reasonable brakes. Its the spongy-ness of them thats the problem, its a really "long" lever that does eventually firm up but you're nearly trapping your fingers by this point and if I adjust it up then I lose what little braking power I had. Bloody annoying really and if I remember correctly it wasn't like this to set off with but I'm not 100% on that bit. Quote Link to comment Share on other sites More sharing options...
jse Posted April 26, 2011 Report Share Posted April 26, 2011 I don't think that its an underlying design fault as at one time they'd be the best available but other bikes older than this that I've had previously (admittedly not trials bike) have still had reasonable brakes. Its the spongy-ness of them thats the problem, its a really "long" lever that does eventually firm up but you're nearly trapping your fingers by this point and if I adjust it up then I lose what little braking power I had. Bloody annoying really and if I remember correctly it wasn't like this to set off with but I'm not 100% on that bit. Generally speaking, on the older type systems the soft initial engagement can be caused by one/both of two things (other than caliper/hydraulic line flex): 1. Tapered bore in M/C due to wear, so that the seal does not fully engage until part way down the bore. The "oversize" diameter in the first part of the bore does not allow the seal lip to fully seal the system. Sometimes a new M/C kit will help but will fail earlier than if the bore was not tapered. As I mentioned, the system is 14 years old and Trials master cylinders get more of a workout than in other forms of motorsports so the possibility exists that you may need a new master cylinder. 2. Air in the system. Probably not the case as I assume you've properly bled it. Jon Quote Link to comment Share on other sites More sharing options...
tltel Posted April 26, 2011 Report Share Posted April 26, 2011 HI I have a 95gg320 and my son has a 94gg125 which both have the two two piston AJP calipers. Both front brakes are very good and will only ever need one finger to stop even on steep long hills and you can easily lock up the wheel if you want. My son is 15 and loves to stand his bike on the front wheel (stoppy). There is very little actual movement in the lever and they both feel solid. I have the short lever and my son has the long levers on his bike. Sounds like you still have air in your system, or as jon said your master cylinder is worn out. I changed a weeping caliper seal on saturday, refitted caliper bled system and all working fine, took about an hour for the whole job and was working great. (it still worked even with the calliper weeping. Basically the brakes are plenty good enough. Also worth mentioning, I only buy cheap pads off Ebay usually about Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 27, 2011 Author Report Share Posted April 27, 2011 HI I have a 95gg320 and my son has a 94gg125 which both have the two two piston AJP calipers. Both front brakes are very good and will only ever need one finger to stop even on steep long hills and you can easily lock up the wheel if you want. My son is 15 and loves to stand his bike on the front wheel (stoppy). There is very little actual movement in the lever and they both feel solid. I have the short lever and my son has the long levers on his bike. Sounds like you still have air in your system, or as jon said your master cylinder is worn out. I changed a weeping caliper seal on saturday, refitted caliper bled system and all working fine, took about an hour for the whole job and was working great. (it still worked even with the calliper weeping. Basically the brakes are plenty good enough. Also worth mentioning, I only buy cheap pads off Ebay usually about Quote Link to comment Share on other sites More sharing options...
hoggyf Posted April 28, 2011 Author Report Share Posted April 28, 2011 Success at last tried the master cylinder off the pit bike and hey presto, stoppies everywhere. So master cylinder repair kit to be ordered and if that doesn't sort it I'll get a new master cylinder complete. cheers all for the help. hoggy Quote Link to comment Share on other sites More sharing options...
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