Let's not start the war.
XT M8000 Brake - no power
- Thread starter FatMuz
- Start date
moorey
call me Mia
Yes. Let's not. The point is, they aren't a DH brake, and aren't marketed as such. :noidea:
And that's why people who buy a dual suspension bike with more than four inches of travel need to stop "upgrading" their brakes to Shimano XT's to "do more downhill". Far out, a young local guy told me a local shop ordered and sold him SLX brakes to handle the extra prolonged heat in a brake for downhilling. He had no idea what he was doing and soon found out the shop didn't either.
How steep and long does coffs get?
udi
swiss cheese
Make sure the caliper seals aren't leaking.
M785 and M666 are notorious for caliper seal failures, have watched at least 10 sets fail locally now (roughly a 50% failure rate - with the others functioning fine), and unfortunately Shimano don't sell any service parts, so you either need to source the seals aftermarket and change them yourself or replace the entire caliper. The failures came with the switch to ceramic pistons (hence previous M775 and M765 calipers did not suffer these issues), and while it's hard to be certain it's the direct cause, it's possible that the fault is not addressed in the M8000 - since it depends how high the global failure rate was.
The telltale sign is "contamination" that repeats itself after cleaning pads/rotors properly or replacing them entirely, where they have enough bite and stopping power temporarily but then go back to the behaviour you describe. Often the user has not actually contaminated the brake but think they have and blame themselves when in reality the brake itself is leaking.
To properly clean pads or rotors that are oil-contaminated, you want to use acetone. The reason for using acetone is that it's a far less polar molecule than other common solvents (like isopropanol or methanol) and thus is superior at dissolving and removing oil. Make sure you clean all parts thoroughly including the inside of the caliper and disc slots to ensure that there are no oily residues remaining. If you can't get acetone, isopropyl (100% only - watch out for additives which can be further contaminants) may be okay - though inferior.
If you're successful, at this point the brake will have a reasonable amount of braking force. The key is to then monitor the brake while ensuring no further contamination occurs (from external sources) and see if the poor braking resurfaces - if so then it's almost guaranteed you've got a leak. If you can't actually clean the brake to a point where it stops / locks up correctly, then you need new or known-good pads to perform the test.
M785 and M666 are notorious for caliper seal failures, have watched at least 10 sets fail locally now (roughly a 50% failure rate - with the others functioning fine), and unfortunately Shimano don't sell any service parts, so you either need to source the seals aftermarket and change them yourself or replace the entire caliper. The failures came with the switch to ceramic pistons (hence previous M775 and M765 calipers did not suffer these issues), and while it's hard to be certain it's the direct cause, it's possible that the fault is not addressed in the M8000 - since it depends how high the global failure rate was.
The telltale sign is "contamination" that repeats itself after cleaning pads/rotors properly or replacing them entirely, where they have enough bite and stopping power temporarily but then go back to the behaviour you describe. Often the user has not actually contaminated the brake but think they have and blame themselves when in reality the brake itself is leaking.
To properly clean pads or rotors that are oil-contaminated, you want to use acetone. The reason for using acetone is that it's a far less polar molecule than other common solvents (like isopropanol or methanol) and thus is superior at dissolving and removing oil. Make sure you clean all parts thoroughly including the inside of the caliper and disc slots to ensure that there are no oily residues remaining. If you can't get acetone, isopropyl (100% only - watch out for additives which can be further contaminants) may be okay - though inferior.
If you're successful, at this point the brake will have a reasonable amount of braking force. The key is to then monitor the brake while ensuring no further contamination occurs (from external sources) and see if the poor braking resurfaces - if so then it's almost guaranteed you've got a leak. If you can't actually clean the brake to a point where it stops / locks up correctly, then you need new or known-good pads to perform the test.
I ridden a hardtail up a five kilometre fire road a bunch of times with a gradient constantly between twelve and sixteen percent. It's fucking terrible actually, I don't know why I keep doing it but have cooked the XT's within the first five hundred metres coming back down on every occasion. I know what they are intended for and it isn't that type of riding. I have a set of SLX on a dual suspension bike and they aren't any different in feel and fade.
Codes or Guides for downsy wownsy. :evil:
dunndog
Eats Squid
Lucky I have guides on kine then huh?! Just a pity my wrist is stuffed and i'm not bringing the cycle machine..
It's five weeks away mate, I have no doubt that you'll be well enough to bring your bike.
dunndog
Eats Squid
Yeah, got too many dive charters booked now haha! will save it for nz.. and a good excuse to get back up your way. see you in 5!It's five weeks away mate, I have no doubt that you'll be well enough to bring your bike.
pink poodle
気が狂っている男
I'm going to agree, but also disagree on this...I know plenty of people who whinge about their shimano brakes not pulling them up, so i can't say it doesn't happen. One buddy wants me to bleed his XT brakes so they feel like another buddy's elixir cr brakes. Shimano brakes tend not to have the skid factor that most other brakes deliver (especially the taper bore) and when i first switched over would have agreed with Dozer.
But I'm 90-95 nude kilos post dump and have been running the XT brakes for many happy years of shuttles and free riding on a variety of different bike. And even with no name baby oil in them. I currently run them on my Pivot with 160mm rotors and have no complaints. none at all. With good braking technique they will haul me up on the local DH trails, Long #enduro drops, and all the short length huck tracks i know.
Minlak
custom titis
Yeah Hopes.....
*I am contractually obliged to quote and agree with JTmofo every time he mentions Hopes
Flow-Rider
Burner
Yep, I think it's how they get improved modulation of the XTs. I'm 80kg and no slouch on the local trails here but they descend fast with lots of berms and switch backs, braking at speeds over 30kms/H, I normally stab my brakes at the last minute before the corners and then just let the bike rip. I normally ride with Avids and Formulas but had test bikes for whole days with XTRs and XTs. I was a bit suspicious when the OP said soft, not spongy brakes and lever going to the grips.
FatMuz
Likes Dirt
Conclusions...
Just thought I'd add some final notes to this thread. Thanks everyone for the many and varied suggestions.
Basically in the end, I got the shits with it all and hung the XT brakes up on the wall and just enjoyed my other bikes. Today I decided to rebuild my Sir 9 for commuting duties next year and realised I'd have to use the dreaded 'cursed' XTs.
I got lazy and installed the brake levers and calipers but left the Sram Centreline rotors on the wheels instead of installing the XT Rotors... and wouldn't you know it... the brakes are performing perfectly. Strong braking power, no noise, feel great.
Is it possible to have contaminated rotors fresh out of the box? Something weird going on there.
But anyway, the XT brakes seem to play just fine with the Sram Centreline rotors.
Cheers.
Just thought I'd add some final notes to this thread. Thanks everyone for the many and varied suggestions.
Basically in the end, I got the shits with it all and hung the XT brakes up on the wall and just enjoyed my other bikes. Today I decided to rebuild my Sir 9 for commuting duties next year and realised I'd have to use the dreaded 'cursed' XTs.
I got lazy and installed the brake levers and calipers but left the Sram Centreline rotors on the wheels instead of installing the XT Rotors... and wouldn't you know it... the brakes are performing perfectly. Strong braking power, no noise, feel great.
Is it possible to have contaminated rotors fresh out of the box? Something weird going on there.
But anyway, the XT brakes seem to play just fine with the Sram Centreline rotors.
Cheers.
pharmaboy
Eats Squid
Not quite, Google a decent article on brakes from an actual mechanic and you'll figure out the problem, rather than the random shite spouted from here (including yours truly). At a guess, I'd go with read up on bedding your brakes in - i didn't read the many wide and varied opinions you would have got, but your first post is either oil on pads or rotors or needed proper bedding in procedure (most people don't frankly, so you aren't alone)
The Duckmeister
Has a juicy midrange
With this update it would appear timely to repost this bit I wrote on the first page....
Your XT rotors were unlikely to be contaminated, just not given the appropriate bedding in treatment, which is essential with metallic pads. It's not a Shimano thing, it's equally valid with all brakes if metal pads are used on new rotors. New pads on old rotors to a lesser extent (the pads need to be scuffed but the rotors are OK), moderately critical for new rotors in older pads, especially critical if the whole set is new.
Knuckles
Lives under a bridge
fatboyonabike
Captain oblivious
was talking to a bike mechanic on the w/e at the lbs, he was trying to fix a new set of 8000's with less than 8 hours on them that were behaving weirdly!
found out that the new ceramic piston in them is also prone to cracking!...that great news, NOT!
found out that the new ceramic piston in them is also prone to cracking!...that great news, NOT!
pharmaboy
Eats Squid
Flow-Rider
Burner
How about you just put up a few good photos of these said rotors and stop our guessing game. Show us what the surface looks like.