Headshot Posted February 22, 2021 Share https://www.mtbr.com/threads/xt-m8000-broken-pistons.1056556/ I got some hardly used looking XT785s (?) from a friend of mine. He had replaced them a while ago but gave no details on what was wrong with them. After a long a tedious bleed process on the front brake, I eventually got normal feeling lever pressure and some brake force up front. Unwisely perhaps I took them for a test on my enduro bike. This involved some 50kph plus rough descents. I survived but noticed the brake power seemed about half of my much older SLX brakes on my other bike and less than the Guide R I had just taken off. I bought some new pads and tried to fit them to find one of the pistons seemed to be jammed out. I decided to strip the caliper and found pretty much what the guy in the MTBR thread above found. The pistons had shattered from the inside and made a crunchy sound when pressed on and the one leaked a bit. My older SLX brakes are by no means perfect but have not developed this kind of terminal issue, yet. The XT brakes in question had seen duty on a marathon bike and may have done some Epics. Still, I can't imagine why a ceramic piston would shatter from the inside. Link to comment Share on other sites More sharing options...
dirtypot Posted February 22, 2021 Share I've come across that before. You can replace the piston if you can get a spare. Check with your LBS - they may have an old caliper lying around. DieselnDust and Headshot 2 Link to comment Share on other sites More sharing options...
fanievb Posted February 22, 2021 Share if you can't find a replacement, I'll gladly take the levers of your hands.my 5y/o 675's are starting to give up the ghost..... Link to comment Share on other sites More sharing options...
Thermophage Posted February 22, 2021 Share https://www.mtbr.com/threads/xt-m8000-broken-pistons.1056556/ I got some hardly used looking XT785s (?) from a friend of mine. He had replaced them a while ago but gave no details on what was wrong with them. After a long a tedious bleed process on the front brake, I eventually got normal feeling lever pressure and some brake force up front. Unwisely perhaps I took them for a test on my enduro bike. This involved some 50kph plus rough descents. I survived but noticed the brake power seemed about half of my much older SLX brakes on my other bike and less than the Guide R I had just taken off. I bought some new pads and tried to fit them to find one of the pistons seemed to be jammed out. I decided to strip the caliper and found pretty much what the guy in the MTBR thread above found. The pistons had shattered from the inside and made a crunchy sound when pressed on and the one leaked a bit. My older SLX brakes are by no means perfect but have not developed this kind of terminal issue, yet. The XT brakes in question had seen duty on a marathon bike and may have done some Epics. Still, I can't imagine why a ceramic piston would shatter from the inside. The takeaway i got from that was...Where did you find 50km/h rough descents? Share ! Patensie 1 Link to comment Share on other sites More sharing options...
droo Posted February 22, 2021 Share Usually it's because the pistons have been forced back in skew at some stage. Piston jams against the gland, gets forced in, chips, then cracks. Replace caliper is your safest bet - usually the sharp edges will cut the piston seal so even a new piston will leak if you can find one. And considering the only place you'll find a spare piston is in a caliper, this is not a hard decision. You should find used calipers with a wanted ad, dead levers are far more common. And all Shimano levers and calipers are cross compatible. DieselnDust and Headshot 2 Link to comment Share on other sites More sharing options...
Headshot Posted February 23, 2021 Share The takeaway i got from that was...Where did you find 50km/h rough descents? Share ! Ha ha - there are a few short steep sections in Cecila, Lower Kirstenbosch and the Green Belts where you can top 50, while being very careful of people and dogs of course. Link to comment Share on other sites More sharing options...
dirtypot Posted February 23, 2021 Share Ha ha - there are a few short steep sections in Cecila, Lower Kirstenbosch and the Green Belts where you can top 50, while being very careful of people and dogs of course. Fast, yes. Fast and rough? Not so much Thermophage and Headshot 2 Link to comment Share on other sites More sharing options...
Headshot Posted February 23, 2021 Share Usually it's because the pistons have been forced back in skew at some stage. Piston jams against the gland, gets forced in, chips, then cracks. Replace caliper is your safest bet - usually the sharp edges will cut the piston seal so even a new piston will leak if you can find one. And considering the only place you'll find a spare piston is in a caliper, this is not a hard decision. You should find used calipers with a wanted ad, dead levers are far more common. And all Shimano levers and calipers are cross compatible.Thanks, yes I have a replacement caliper already and have a front brake up and running. What seems to be a harder job is finding a long piece of hose with a banjo attachment on the end... Not even Shimano seem to have stock. Link to comment Share on other sites More sharing options...
Headshot Posted February 23, 2021 Share Fast, yes. Fast and rough? Not so much It depends on your definition. I call anything with loose baby heads, loose corners and ruts "rough" and there are plenty of segments like that around. Link to comment Share on other sites More sharing options...
DieselnDust Posted February 23, 2021 Share Thanks, yes I have a replacement caliper already and have a front brake up and running. What seems to be a harder job is finding a long piece of hose with a banjo attachment on the end... Not even Shimano seem to have stock. I may have spares if you can send me a pic of the hardware you need Link to comment Share on other sites More sharing options...
Headshot Posted February 23, 2021 Share I may have spares if you can send me a pic of the hardware you needThx, right now all I need is a 1.7 m plus length of brake line with a Shimano banjo fitting on one end. Link to comment Share on other sites More sharing options...
DieselnDust Posted February 23, 2021 Share Thx, right now all I need is a 1.7 m plus length of brake line with a Shimano banjo fitting on one end. let me go do the scrounging in the garage. get back to you shortly Headshot 1 Link to comment Share on other sites More sharing options...
Thermophage Posted February 23, 2021 Share Ha ha - there are a few short steep sections in Cecila, Lower Kirstenbosch and the Green Belts where you can top 50, while being very careful of people and dogs of course. And here I was hoping you meant singletrack/trails So Pat's is still the fastest rough trail you can get ... possibly in the WC? hmm Headshot 1 Link to comment Share on other sites More sharing options...
Headshot Posted February 24, 2021 Share And here I was hoping you meant singletrack/trails So Pat's is still the fastest rough trail you can get ... possibly in the WC? hmmThere are some bits of single track in the mix but they are short and over very quickly at speed. Pats is on another level of course. Link to comment Share on other sites More sharing options...
Headshot Posted March 1, 2021 Share I may have spares if you can send me a pic of the hardware you needThanks for the hose DnD - XT's are up and running. Next upgrade is new Shimano rotors and some genuine Shimano pads. DieselnDust 1 Link to comment Share on other sites More sharing options...
DieselnDust Posted March 1, 2021 Share Thanks for the hose DnD - XT's are up and running. Next upgrade is new Shimano rotors and some genuine Shimano pads. awesome , glad to be able to help out Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now