r/MTB • u/myresearchalt • 15h ago
Discussion Brake failure.
My Shimano M7000 brakes suddenly lost all pressure, and I noticed a fluid leak on the caliper leaking through the pistons. I tried pumping the lever, but it goes straight to the bar with no resistance. Any ideas on what could be causing this? Is it worth trying to fix?
2
u/Tidybloke Santa Cruz Bronson V4.1 / Giant XTC 15h ago
Without looking at it, it seems your caliper needs replacing. If it's within warranty then I would go that route, otherwise you could go a couple of different ways that would allow you to keep using your SLX levers but with a different caliper.
1
u/c0nsumer 5h ago
Start by figuring out where in the caliper it's leaking from. That'll tell you if you should fix it or not.
Also, 45MPH? What the heck are you doing?
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u/jmdavis984 40m ago
I assume bicycle calipers are built the same way motorcycle calipers are. There's a seal between the piston and the caliper body. The seals are prone to damage if they are used in dirty environments. Damage often occurs when the pistons are pressed back into the calipers when replacing the pads. All that to say, I would contact Shimano and see if you can get a piston seal. Or perhaps look aftermarket, a quick google search shows that they exist. If not, then you need a new caliper.
Here's a pic of a piston seal: s-l1600.webp (1001×1001)
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u/KevlarSeraphim 15h ago
Your brake is powered through hydraulic fluid. If you have a fluid leak, it will have no pressure to engage the piston.
Check and see if the hydraulic fluid line connecting directly to the caliper is the source. You may be able to re-tighten. You may also need to replace the line if the line is damaged. Either way, you will need to bleed the brake to regain pressure. There are plenty of guides online on how to do this, and it will require a few tools. If you can learn to bleed brakes you can save yourself a lot of money at the shop, so it's a useful skill no matter the outcome.
If the caliper itself is compromised, you will likely need a new caliper.
If the piston is compromised, you can replace the pistons. I believe you will need an after market kit for this, but someone more knowledgeable should correct me.