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Hi. I have Shimano M8020 brakes (xt, 4 piston) and I have to bleed them regularly as they seem to be taking air in.
After bleeding, they work really well (I have never had the variable bite point problem) and have bled them by following shimanos instructions and also doing the top down method.
After 8-10 rides,the levers start coming closer and closer to the bars when I am braking.
I got fed up doing a full bleed every few weeks, so have started doing regular 'mini bleeds' where I use the shimano bleed funnel, and press the lever (at different angles) to expel the many air bubbles that appear.
There is no sign or fluid escaping the lever, hose connections or the caliper/pistons, however air is clearly getting in/fluid escaping, or both.
Any ideas how to fix this? (and no, I don't want to change them for hope, sram etc brakes!)
(and no, I don’t want to change them for hope, sram etc brakes!)
That's your problem lol Shimano really seem to have lost the plot with brakes
Are they still under waranty, they may need to be returned to the shop then the shop can forward them onto Shimano who will pressure test them for any micro leaks which you and the shop cant detect
This is what i had to do with my last and final set of Shimano brakes
Shimano said they had a micro leak at the pistons and sent me a brand new set which went straight on ebay and Hope's were bought to replace them, never looked back, never had a bad brake since!
Definitely not just pad wear? 🤔
Surely if it was air they'd feel spongy.
they should correct for pad wear - thats the advantages of hydros. sounds to me like a blown master cylinder seal. Its the most likely place for the air to be getting in. Any moisture around the lever?
When you do you mini service are you adding oil?
I used to have a pair of shimano brakes and id tie them up over night with string, keep tapping the hoses to try and get air out. Felt great next day riding but wouldnt last.
I also used to put kitchen roll on the calipers to check for leaks but couldn't find any.
In the end it was a sticky piston (possibly master as above) in the levers. Brakes would bind when the weather was hot.
I stripped them, cleaned them, put them back together and they were fine at night, next day in the sun they would bind. Had to buy new levers.
When you've bled them, what colour was the oil that came out? You could try draining all the mineral oil out and putting in fresh if it's dirty but I doubt it will work.
Have you tried over filling them? Not always advised but this is a good video.
Sounds like pad wear. I find with shimanos you need to wind the reach out as the pads wear to keep the bite point where you want it. Turn the bike upside down and see if they pull to the bar. If there’s air in there will be a noticeable difference.
Sounds like you need new brakes. Preferably not Shimano.
Can you advance the pads to rectify the issue? Is the lever going spongy at all?
It isn't pad wear - plenty air bubbles come out when I do a bleed or 'micro bleed.
Fluid is clear - as I am regularly topping it up, it doesn't get a chance to get dirty.
Lever not spongy but perhaps I'm not letting it get to that stage due to the regular bleeds.
Brakes are out of warranty. Where can I source spare master cylinders?
Is this the same on both brakes??
After 8-10 rides,the levers start coming closer and closer to the bars when I am braking.
If it's due to air, they will feel spongy. If it's due to pad wear, they will have a solid feel at the lever.
If air's getting in, fluid must be getting out. The seals at the master cylinder seem the most likely source of this, as TJ pointed out.
I had new XT on my Ebike and front was great,Rear was sh1t,Was doing same as you every now and then I’d do lever purge to get the air out
There was so many turns in the hose through the frame it was mad,I bought Magura MT5 brakes and low n behold,Same bloody problem on the rear🙈
If you have air getting in, you either have a leak you aren't noticing, you're not bleeding them as well as you think, Or your pads are fairly low. (Last one depends on whether you use a bleed block or not)
In my case on the other thread, I had low grade leaks on both levers - the gubbins behind the lever pivot was oily and had collected debris.
You're describing a common aspect of the various problems that shimano brakes have had for years. Mine are exactly the same as yours and need bleeding every 10 rides or so. Everyone will tell you that you just need to bleed them properly, but they are wrong, don't waste your time on this aspect - it's worse than that - I know this for sure after countless wasted hours and pro mechanic workshop time chasing the issue. They will be letting air into the system through normal operation possibly through calliper seals or lever seals or both, you won't detect it visibly. I bet every time you bleed them, even if you did it every ride, there will be lots of air bubbles in the system that certainly weren't there before...If you find a solution let us know as I've given up on mine. If they are in warranty then warranty them.
Are there any after market pistons and seals available for the Shimano 8120 calipers?
My brakes are squealing and suspect a leak around the pistons
Was gonna give you a long boring story bout me LBS but won't, the punch line being they left off the rubber washer on the lever reservoir screw.
they left off the rubber washer on the lever reservoir screw.
I bet it was transferred to the funnel and they didn't notice, Then removed the funnel and put the screw back in. Easily done if your not looking out for it.
Easily done if your not looking out for it.
easily done if you’re not a professional outfit frequently being paid to do the job to a standard
The only quibble I have with my 4 pot xts is an occasional need to push the levers fully away from the bars to ensure they adjust for pad wear - I run the levers quite wound in and seems they don't always go out far enough to compensate at the lever. I'm talking once (as in one push) every couple of months, not every 10 rides though.
Yep I'd say the same but it went back 2 more times then bullshit boy who fitted them said it was a problem inside the lever I'd need a new lever so after 6 months on one brake bought the bits to have a go bleeding them myself after looking on YouTube and after doing the working brake first did the rear and noticed it missing as soon as I unscrewed it I just used the one on the bottom of the pot for bleeding and is now fine.
Just to add not same model as op.
Hi, thanks for the replies so far. I definitely still have the rubber o-rings attached to the bleed ports!
I have been puting up with this for months, so it isnt old pads, and doubtful it is due to pad wear, as there shouldn't be bubbles in the system.
My wife has wife has the same brakes and have no problems with them and I am 99.9% confident that I am bleeding them properly. (Even if I was mis-bleeding them, the would eventually run out of air bubbles - these keep reappearing after a few rides).
If I have a micro leak (absolutely no sign of fluid escaping the lever/caliper/pistons), where can I source a new master cylinder and/or piston seals. Surely spares must be available?
the only spares are whole calipers or levers. No seals
It will be a master cylinder seal gone - that gives exactly the symptoms you describe