nox1111 Posted January 21, 2016 Share I have this theory that if your disc brakes work, don't touch them. Other than change pads, I don't let a bikeshhop touch my brakes. My XTR rear brake started feeling as if there's a little bubble in the line the last couple of rides, and especially when on a long dh section, the brake will pull a lot closer to the bar than normal. And so I did the unthinkable and took my bike to my LBS and with a heavy heart I asked them to bleed my super crisp feeling XTR rear brake - only to sort out the 'when hot' problem. I pick up my bike today and worst fear realized, my brake has no more kick back. If you pull any Shimano brake and it has a swift spring back to it's original position. That is no more the case, and mine slowly/sloth-ly moves back to its original position. It is still potent, but there's no modulation, because there's no kickback, so the brake stays where it is, and if you pull too far, wheel just locks up - and very abruptly. LBS is stumped, I'm furious and also stumped. They have no idea why its acting like this or what could go wrong. Anyone know why this would happen and how to fix it? My brake's character is just not what it used to be, and I won't attempt to manual sections like that, and if a Tektro Auriga felt like that, I would still suspect something went wrong. Link to comment Share on other sites More sharing options...
gummibear Posted January 21, 2016 Share Sounds like a sticky master cylinder. Ryno., Captain Fastbastard Mayhem and raptor-22 3 Link to comment Share on other sites More sharing options...
Bobbo_SA Posted January 21, 2016 Share Sounds like a sticky master cylinder. That or the spring between the pads has been left out. gummibear 1 Link to comment Share on other sites More sharing options...
Spoke101 Posted January 21, 2016 Share Sounds like your brakes master cylinder could be on its way out. Try pulling the brake hard and keep sustained constant pressure on the lever. if it slowly goes to the bar then your master cylinder in the lever is shot and you need a new lever. JXV 1 Link to comment Share on other sites More sharing options...
nox1111 Posted January 21, 2016 Share Sounds like your brakes master cylinder could be on its way out. Try pulling the brake hard and keep sustained constant pressure on the lever. if it slowly goes to the bar then your master cylinder in the lever is shot and you need a new lever.The spring back on my front feels more like an actual mechanical spring, rather than something that the cylinder and fluid is responsible for - I would guess that even if you emptied the brake, it would still have that swift springback. Like what a cable disc brake lever would have, if you took everything off and just pulled the lever. Why would a busted cylinder prevent the brake from opening quickly? Link to comment Share on other sites More sharing options...
nox1111 Posted January 21, 2016 Share Sounds like a sticky master cylinder.Shot GB, How do I check this and how do I fix it? any ideas? Link to comment Share on other sites More sharing options...
nox1111 Posted January 21, 2016 Share That or the spring between the pads has been left out.It's in the lever - the brake releases the disc immediately after you release it, with no drag. Link to comment Share on other sites More sharing options...
dirtypot Posted January 21, 2016 Share Why would a busted cylinder prevent the brake from opening quickly? That spring back is a result of the pressure in the master cylinder. If the seals have failed and there is not enough pressure in the line, then there will be no strong spring back. This is a relatively common Shimano issue if you don't regularly bleed your brakes. You'll probably find that the fluid that came out when they were bled was black sludge. This damages the seals, so the fluid goes past the seals and back into the master cylinder instead of into the brake line. Spoke101 1 Link to comment Share on other sites More sharing options...
Spoke101 Posted January 21, 2016 Share The spring back on my front feels more like an actual mechanical spring, rather than something that the cylinder and fluid is responsible for - I would guess that even if you emptied the brake, it would still have that swift springback. Like what a cable disc brake lever would have, if you took everything off and just pulled the lever. Why would a busted cylinder prevent the brake from opening quickly? The reason for the slow return is that fluid gets pushed the wrong side of the master cylinder main seal. Shot GB, How do I check this and how do I fix it? any ideas? You can't really do anything, Shimano doesn’t sell spears and they not serviceable.Certain shop can open them and try replacing the master cylinder with another used but better condition one. Link to comment Share on other sites More sharing options...
nox1111 Posted January 21, 2016 Share The reason for the slow return is that fluid gets pushed the wrong side of the master cylinder main seal. You can't really do anything, Shimano doesn’t sell spears and they not serviceable.Certain shop can open them and try replacing the master cylinder with another used but better condition one.I seriously hope that this is not the case! Sheet! I found this service manual - http://cycle.shimano-eu.com/media/techdocs/content/cycle/SI/XTR/SI_8J70A/SI-8J70A-005-00-Eng_v1_m56577569830780905.pdf and there's a little screw that does Free Stroke adjustment - I'm wondering if whomever bled the brake did not screw this in or out without thinking?! Link to comment Share on other sites More sharing options...
gummibear Posted January 21, 2016 Share You can't really do anything, Shimano doesn’t sell spears and they not serviceable.Certain shop can open them and try replacing the master cylinder with another used but better condition one.It's not easy to do and takes time so will cost a bit.Although with Rand where it is it might be cheaper to swop. I could also be as simple as it wasn't bled properly. Link to comment Share on other sites More sharing options...
Pete the Pirate Posted January 21, 2016 Share GOSH DARN I have the XTR M980 Race that I purchased off of the Hub. The rear level pulled flat to the bar. My LBS run by Paul Farrance (Ex Barloworld head wrench) hoped that it was not the seals (which it was not and it now runs perfectly). He says that the new Shimano brakes have to be bled specifically in one direction with no reverse flow of fluids as this causes the seal to 'roll' or 'invert' rendering the brake useless. These parts cannot be serviced. Good luck. Spoke101 1 Link to comment Share on other sites More sharing options...
s14phoenix Posted January 21, 2016 Share Ant then there is the dreaded "I put new dot fluid in and bled the system perfectly" from the mech in which case your mineral oil ONLY shimano are F#$%-ed and the seals have swollen and screwed... I had a similar when the box put mineral oil in a set of avid juicy 3 brakes... hope you come right. Link to comment Share on other sites More sharing options...
Spoke101 Posted January 21, 2016 Share I seriously hope that this is not the case! Sheet! I found this service manual - http://cycle.shimano-eu.com/media/techdocs/content/cycle/SI/XTR/SI_8J70A/SI-8J70A-005-00-Eng_v1_m56577569830780905.pdf and there's a little screw that does Free Stroke adjustment - I'm wondering if whomever bled the brake did not screw this in or out without thinking?! That little free stroke screw is useless it does nothing (It make at a 5% difference that’s a lot), but that doesn’t show you how to remove and replace the master cylinder GOSH DARN I have the XTR M980 Race that I purchased off of the Hub. The rear level pulled flat to the bar. My LBS run by Paul Farrance (Ex Barloworld head wrench) hoped that it was not the seals (which it was not and it now runs perfectly). He says that the new Shimano brakes have to be bled specifically in one direction with no reverse flow of fluids as this causes the seal to 'roll' or 'invert' rendering the brake useless. These parts cannot be serviced. Good luck. You are correct, some of the Shimano service manuals state that you should push fluid up from the calliper. This is completely trash and doing this will flod your master cylinder seal and ruin your brake. Shimano's should only be gravity bled and there are a few trick to get all the air out and adjust the free stroke that actually works. Edited January 21, 2016 by Spoke101 Pete the Pirate 1 Link to comment Share on other sites More sharing options...
Thermophage Posted January 21, 2016 Share That little free stroke screw is useless it does nothing (It make at a 5% difference that’s a lot), but that doesn’t show you how to remove and replace the master cylinder You are correct, some of the Shimano service manuals state that you should push fluid up from the calliper. This is completely trash and doing this will flod your master cylinder seal and ruin your brake. Shimano's should only be gravity bled and there are a few trick to get all the air out and adjust the free stroke that actually works.Sheesh I'd love a guide on this if you have as every resource I have managed to find says bleed from caliper up, then slight gravity fed bleed back down again :S Link to comment Share on other sites More sharing options...
Spoke101 Posted January 21, 2016 Share Sheesh I'd love a guide on this if you have as every resource I have managed to find says bleed from caliper up, then slight gravity fed bleed back down again :SI'll see if I can put something together if I get some free time. I might have to do it as a video as some of the stuff is hard to explain and comes for years of doing this day in and out. nox1111 1 Link to comment Share on other sites More sharing options...
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