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My trail bike has XTR m9000 levers, with a m9000 rear caliper and a slightly older Saint 4pot front caliper.
Both are bled well and have a firm lever feel. However, the rear appears to be exhibiting the symptoms of the old M785 leaky pistons - that is; take the pads out, clean and bake them in the oven, clean the rotor with disc cleaner / isopropanol, and then the brakes work fine and lock the rear wheel with the lightest of touches once bedded. A week later, then rear brake squeals like a banshee and won't actually even lock the rear wheel. As in; ride down a hill, throw two fingers around the lever and haul like a monster and the rear wheel keeps spinning (180mm rotor).
I thought this issue was limited to the older generation brakes? Before I ruin my spare pads, is there any way of troubleshooting this?
I think you have troubleshooted this. Might as well get a matching saint caliper to replace it.
I’ve gone through 7 XTR callipers, both M9000 and M9020. The longest lasting were on the commuter in regular use and lasted 4.5years for the front and the rear was still okay. On the irregularly used MTBs - I got less than 18m for 3 sets.
These were all one piece callipers.
Yes they do but they come with a 3 year warranty!
Q) Do they leak?
A) Were they made by Shimano?
Q) Do they leak?
A) Were they made by Shimano?
and you think you don’t need to do a full bleed
Funny thing, people think maintenance only applies when they stop working. Every Shimano jammed lever or leaky caliper ive ever seen the owner thinks they don’t need to do a full bleed. Not to say there are not some genuine failures but running dirty oil is by far the main reason.
With DOT brakes people are forced to bleed but mineral oil will keep working right until it doesn’t
I only choose to bleed my Hope brakes and replace the fluid once a year. I think they'd easily manage 2.
How often are you recommending a flush in Shimano systems?
Not to say there are not some genuine failures but running dirty oil is by far the main reason.
With DOT brakes people are forced to bleed but mineral oil will keep working right until it doesn’t
How does the oil get dirty if it's a sealed system?
I've run DOT brakes for over 10 years without bleeding. They keep on working. (Not saying you'd want to do that if you were racing DH, but the flushing fluid thing is a bit over-hyped.)
They had a full flush with shimano oil (it was previously the green stuff) recently. Ok, I'll find a new caliper.